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Background:. Middle facet subluxation (MFS) has been established as an early indicator of peritalar subluxation. However, when progressive collapsing foot deformity (PCFD) affects the ankle leading to a valgus talar tilt (Class E), structures and anatomic relationships distal to the ankle joint may be affected. Therefore, this study aimed to assess radiographic parameters of peritalar subluxation in patients with PCFD who either did or did not have a valgus ankle. Our hypothesis was that these parameters would differ in Class E patients, upsetting their capability to quantify deformity. Methods:. We performed a prospective comparative study utilizing weight-bearing computed tomography (WBCT) images of 21 feet with PCFD and with valgus of the ankle and 64 with flexible PCFD without ankle involvement. Parameters including MFS, the medial cuneiform-to-floor distance, the forefoot arch angle, the talonavicular coverage angle, the hindfoot moment arm (HMA), the foot-ankle offset (FAO), and the talar tilt angle (TTA) were measured and compared. Variables that influence the presence of ankle valgus and overall alignment were assessed by multivariable regression models. Results:. Patients with PCFD and ankle valgus demonstrated a higher mean HMA (20.79 mm [95% confidence interval (CI), 17.56 to 24.02 mm] versus 8.94 mm [95% CI, 7.09 to 10.79 mm]), FAO (14.89% [95% CI, 12.51% to 17.26%] versus 6.32% [95% CI, 4.96% to 7.68%]) and TTA (95% CI, 17.10° [14.75° to 19.46°] versus 2.30° [95% CI, 0.94° to 3.65°]) and lower mean MFS (21.84% [95% CI, 15.04% to 28.63%] versus 38.45% [95% CI, 34.55% to 42.34%]) compared with the group without ankle valgus (p < 0.0001 for all). The FAO was influenced by MFS in the group without ankle valgus (p

Abstract A key element of the peritalar subluxation (PTS) seen in progressive collapsing foot deformity (PCFD) occurs through the transverse tarsal joint complex. However, the normal and pathological relations of these joints are not well understood. The objective of this study to compare Chopart articular coverages between PCFD patients and controls using weight-bearing computed tomography (WBCT). In this retrospective case control study, 20 patients with PCFD and 20 matched controls were evaluated. Distance and coverage mapping techniques were used to evaluate the talonavicular and calcaneocuboid interfaces. Principal axes were used to divide the talar head into 6 regions (medial/central/lateral and plantar/dorsal) and the calcaneocuboid interface into 4 regions. Repeated selections were performed to evaluate reliability of joint interface identification. Surface selections had high reliability with an ICC > 0.99. Talar head coverage decreases in plantarmedial and dorsalmedial (− 79%, p = 0.003 and − 77%, p = 0.00004) regions were seen with corresponding increases in plantarlateral and dorsolateral regions (30%, p = 0.0003 and 21%, p = 0.002) in PCFD. Calcaneocuboid coverage decreased in plantar and medial regions (− 12%, p = 0.006 and − 9%, p = 0.037) and increased in the lateral region (13%, p = 0.002). Significant subluxation occurs across the medial regions of the talar head and the plantar medial regions of the calcaneocuboid joint. Coverage and distance mapping provide a baseline for understanding Chopart joint changes in PCFD under full weightbearing conditions.

Category: Midfoot/Forefoot; Basic Sciences/Biologics; Hindfoot Introduction/Purpose: The current classification system of progressive collapsing foot deformity (PCFD) is comprised of 5 possible classes that describe different deformity components. Each class is defined by clinical and radiographic findings. These components are ostensibly independent from one another during evaluation and treatment. However, PCFD is understood to be a complex, three-dimensional deformity occurring in many regions along the foot and ankle. The question remains whether a deformity in one area impacts other areas. The objective of this study is to assess how each one of the classes is influenced by other classes by evaluating each associated angular measurement. We hypothesized that positive and linear correlations would occur for each class with at least one other class and that this influence would be high. Methods: In this IRB-approved retrospective case-control study, we assessed 32 feet diagnosed with PCFD and 28 controls matched on gender, BMI and age. All measurements were performed using weight-bearing CT (WBCT) scans and completed by two foot and ankle surgeons. The classes and their associated radiographic measurements were defined as follows: Class A (hindfoot valgus) measured by the hindfoot moment arm (HMA), class B (midfoot abduction) measured by the talonavicular coverage angle (TNCA), class C (medial column instability) measured by the talus-first metatarsal (Meary) angle, class D (peritalar subluxation) measured by the medial facet uncoverage (MFU), and class E (ankle valgus) measured using the talar tilt angle (TTA). Multivariate analyses were completed comparing each class measurement to the other classes. Data were checked for multicollinearity with the Belsley-Kuh-Welsch technique. Heteroskedasticity and normality of residuals were assessed respectively by the Breusch-Pagan test and the Shapiro-Wilk test. A p-value

Category: Midfoot/Forefoot; Bunion Introduction/Purpose: Kim et al.'s simulated weight-bearing CT (WBCT) investigation classifying first metatarsal (M1) pronation and its relationship to the metatarso-sesamoid complex suggested a high prevalence (87.3%) of M1 hyper-pronation in hallux valgus (HV). These authors' conclusions have prompted a marked increase in M1 derotation (supination) in HV surgical correction. No subsequent study confirms their M1 pronation values, and two recent WBCT investigations suggest lower normative M1 pronation values. The objectives of our WBCT study were to (1) determine M1 pronation distribution in HV, (2) define the hyperpronation prevalence compared to preexisting normative values, and (3) assess the relationship of M1 pronation to the metatarso-sesamoid complex. We hypothesized identifying a high HV M1 head pronation distribution, but not as high as suggested by Kim et al. Methods: We retrospectively identified 88 consecutive feet with HV in our WBCT dataset and measured M1 pronation with two previously validated methods, the Metatarsal Pronation (MPA) and α angles. Similarly, using two previously published methods defining the pathologic pronation threshold, we assessed our cohort's M1 hyper-pronation prevalence, specifically (1) the upper value of the 95% confidence interval (CI95) and (2) adding 2 standard deviations at the mean normative value (2SD).The position of the sesamoids relative to the crista on the axial plane (sesamoid grading) was assessed according to Talbot et al. classification secondarily adapted by Yildirim et al. on CT scan (Figure).Normality of different variables was assessed using the Shapiro-Wilk test and distribution histogram. Two groups were compared using Student's t-test for normal, and Mann-Whitney U test for non- normal variables. P values less than .05 were considered significant. Results: The mean MPA was 11.4+/-7.4 degrees (IC95%:9.9-13.0; Range: -2.3-37.1) in our HV population and the α angle was 16.2+/-7.4 degrees (IC95%:14.7-17.7; Range: 2.8-43.2). A strong positive correlation was found between these two variables (ρ=0.82;r2=0.79;P

Category: Ankle Arthritis; Ankle Introduction/Purpose: In varus-type osteoarthritis of the ankle (VAOA), it is known that the subtalar joint compensates in valgus/eversion for the malalignment of the tibiotalar joint. However, previous studies were mainly based on X-ray measurements and did not take into account peri-talar changes that extend to the subtalar and Chopart joints. Furthermore, the effect on peritalar compensation when tibio-talar arthrodesis is performed is still unclear. Distance Mapping (DM) is a technology that can produce a 3D point-to-point distance map of joint interactions from cone beam weight bearing CT (WBCT) images. The purpose of this study was to quantify the peri-talar changes that occur when the tibiotalar joint is fused. We hypothesized that talar varus would improve and that the Chopart/Subtalar joint complex would present compensatory varus/inversion. Methods: The subjects were 14 patients (15 feet) who underwent arthrodesis for VAOA at our institution. The average postoperative follow-up period was 6.6 months. Foot alignment (Foot Ankle Offset (FAO)) was measured from WBCT datasets pre and postoperatively. The pre to post op shift vectors of the weighted distance maps center points were measured for the tibiotalar, subtalar, calcaneocuboid and talonavicular joints. Statistical analysis was performed by paired T-test, and the significance level set at p

Category: Bunion; Hindfoot; Midfoot/Forefoot Introduction/Purpose: The presence of hyperpronation of the first metatarsal (M1) seems to have a clinically significant role in Hallux Valgus (HV). Some authors reported a decrease in recurrence rates after M1 hyperpronation correction in HV. However, when measuring the M1 head pronation relative to the ground, we are assessing and quantifying the aggregate coronal rotational profile of each bone and joint throughout the medial column. Therefore, we do not know the location of this hyperpronation. Moreover, studies showed a strong influence of the hindfoot alignment on coronal rotational measurements and Progressive Collapsing Foot Deformity (PCFD) is a condition frequently associated with HV. Our study aimed to assess and compare coronal plane alignment of medial column bones in HV, PCFD, PCFD HV and controls. Methods: We performed a retrospective IRB approved study. We collected 33 feet who consulted our center with combinations of symptomatic PCFD and HV. We then matched 33 HV, 33 PCFD, and 33 controls for BMI, Gender, and Age to this group. We assessed the coronal plane rotation of the navicular, medial cuneiform, M1 at its base and head, the Sesamoid Rotation Angle (SRA) with respect to the ground, and the hallux valgus angle (HVA) using Weight-Bearing CT images (Figure).The positions of the different joints (first naviculocuneiform (NC1), first tarsometatarsal (TMT1) and metatarsosesamoid rotation angle (MSRA)) were found by subtracting the adjacent angles. Intrinsic torsion of M1 was calculated by subtracting the M1 base angle from the M1 head angle.Normality of different variables was assessed using the Shapiro-Wilk test. Groups were compared using t test or ANOVA for normal and Mann Whitney or Kruskal Wallis for nonnormal variables. Results: HV, PCFD and PCFD HV presented higher M1 intrinsic torsion when compared to controls (respectively 7.3°[CI95%:2.9-11.7], p

Category: Ankle; Basic Sciences/Biologics; Hindfoot Introduction/Purpose: Abnormal Hindfoot Alignment (HA) has been correlated with increased complication rates in ankle fusion or replacement. Altered Bone Mineral Density (BMD) due to abnormal stress distribution could be predisposing factor for those unwanted outcomes. The objective of this study was to assess spatial distribution of BMD around the ankle joint in patients with normal or abnormal HA using cone beam Weight Bearing CT. Methods: Retrospective comparative study including 81 ankles allocated into 3 groups based on the Foot Ankle Offset (FAO): 27 normal (0%5%). groups were comparable by age (p=0.967), Body Mass Idex (p=0.669), sex (p=0.820) and side (p=0.708). Semi- automatic segmentation (BoneLogic, Disior) was applied to identify bones. Tibia and talus were digitally compartmented in medial (M) and lateral (L) volumes relative to the median sagittal plane. Mean Hounsfield Unit (HU) value per compartment was used to assess BMD and to calculate the Medial over Lateral HU ratio (M/L-HU). Comparisons among the three groups were performed using one-way ANOVA, Kruskal-Wallis and Chi 2 tests. Results: Mean +- standard deviation HU values in the compartments in normal cases were 495.2+-110 (medial tibia), 495.6+- 108.1 (lateral tibia), 368.9+-80.3 (medial talus), 448.2+-90.6 (lateral talus) and 686.7+-120.4 (fibula). Upon comparison of the mean BMD value for each compartment in the three groups, the difference did not achieve statistical significance. Conversely, the tibia HU-M/L ratio (0.88+-0.14 in valgus cases, 0.99 +- 0.08 in normally-aligned cases and 1.04+-0.08 in varus cases) and the talar HU- M/L ratio (0.68+-0.18 in valgus cases, 0.82+-0.08 in normally-aligned cases and 0.96+-0.20 in varus cases) were significantly different in the three groups (p

Category: Bunion; Midfoot/Forefoot Introduction/Purpose: The utility of Lateral soft tissue release (LSTR) in the setting of percutaneous Hallux Valgus (PHV) surgery is still debated. Our aim was to conduct a systematic review of the literature comparing the results of PHV surgery with and without LSTR in order to define the benefits and risks related to this procedure. Our hypotheses were that LSTR would 1) reduce the risk or recurrence of the deformity without increasing the risk of complication and 2) lead to an improved clinical outcome with greater radiological correction. Methods: This systematic review followed the PRISMA checklist and was prospectively registered in the Prospero database (CRD4202230). Pubmed, Embase, Cochrane Library and Scopus were used to identify clinical papers reporting results after PHV surgery. Studies were pooled in two categories: PHV with LSTR (Group 1 or G1) and PHV without LSTR (Group 2 or G2). Data regarding the study design, demographics, the surgical procedure and the clinical and radiological outcome were extracted and compared. The modified Coleman Methodology score (mCMS) was used to assess the quality of studies included. Results: Sixteen studies were selected (G1:594 feet;G2:553 feet). The sample size (p=0.11), sex distribution (p=0.57), length of follow-up (p=0.79), size of the incision (p=0.13) were comparable. Studies in G2 included a younger population (54+-6.3 vs 44.4+- 6.8 years;p=0.006), however age did not correlate with the clinical and radiological outcome (all p>0.05). The pooled proportion of complication in the two groups (27%, 95%CI 17-38 and 25%, 95%CI 12-37, respectively) and the pooled proportion of recurrence at a minimum 18-month follow-up (2%, 95%CI 0-3 and 2%, 95%CI 0-5, respectively) didn't differ (p=0.79 and p=0.70). The pre- (51.7+-10.6 and 45.8+-1.7 points;p=0.23) and post-operative AOFAS scores (89.4+-4.3 and 86.9+-3.2 points;p=0.16) and the pre-(HVA:29.7+-2.9 and 44.1+-26.8 degrees,p=0.23)(IMA:12.5+-4.2 and 14.1+-2.6 degrees;p=0.94) and post-operative radiological angles (HVA:12.1+-4.3 and 12.3+-2.3;p=0.47)(IMA:9.2+-2.2 and 7.9+-1.3;p=0.2) didn't differ in the two groups. The methodological quality of studies (mCMS: 68.7+-11 points in G1, 63.4+-14.3 points in G2;p=0.2) was similar in G1 and G2 Conclusion: Lateral soft tissue release during percutaneous HV surgery does not seem to improve the clinical and radiological outcome nor reduces the risk of recurrence of the deformity at a mean 4-year follow-up.

Category: Hindfoot; Midfoot/Forefoot; Other Introduction/Purpose: Progressive collapsing foot deformity (PCFD) is a complex three-dimensional (3D) deformity characterized by peritalar subluxation (PTS) of the hindfoot through the triple joint complex. In this context, adjacent structures adopt different positions, and bone relations change, producing areas of higher or less contact and stress. The objective of this study was to use 3D distance maps (DMs) and coverage maps (CMs) from weightbearing CT (WBCT) images to assess subluxation across the Chopart joint in PCFD patients. We hypothesized that CMs would show decreased coverage indicative of subluxation through regions of the Chopart joint in PCFD patients when compared to controls. Methods: In this IRB-approved, retrospective case-control study, we analyzed WBCT data of 20 consecutive patients with flexible PCFD and 20 controls. Using principle component analysis, coverage area was divided into six regions on the talar head and 4 on the calcaneal-cuboid articular surface. Novel 3D distance mapping (DM) technique was used to objectively characterize joint coverage across the entire Chopart surface on both talus and calcaneus. Distance maps were measured in millimeters and colored to highlight covered areas. Distances less than 4mm were defined to be covered, while areas with distances greater than 4mm uncovered. Joint coverage was defined as percentage of articular area with DMs lower than 4 mm. Coverage Maps (CM) were built highlighting areas of coverage (teal) versus non-coverage (pink). The Foot and Ankle Offset (FAO) was used as a reference semi-automatic three-dimensional measurement. Comparisons were performed with independent t-tests, assuming unequal variances and p-values 0.05). The FAO was found to be correlated with changes in talar and calcaneal coverages (rs=0.90; R2=0.81). Conclusion: Our results support the hypothesis that significant changes occur at the Chopart joint in early flexible PCFD cases. Increased coverage in the lateral region of the talar head and decreased coverage in the medial and plantar regions point to internal rotation of the talus indicating subluxation through the entire joint. This behavior was also translated in the calcaneal- cuboid, where plantar and medial areas had a decrease in coverage. Coverage 3D mapping enabled objective subluxation quantification through the Chopart joint in early-stage PCFD. These findings may assist clinical assessment of normal joint alignment restoration during PCFD corrections.

Category: Ankle Arthritis; Ankle Introduction/Purpose: Ankle arthrodesis, well-known as a reliable option to treat end-stage ankle osteoarthritis (AO), may be fixed using screws in various configurations. The purpose of this study was to determine whether the number of screws and the use of a lateral distal fibular autograft during the procedure might influence the union and complication rate. We hypothesized that a greater number of screws and the use of a fibular autograft might increase the union rate and reduce the number of complications. Methods: Following the PRISMA-compliant PROSPERO-registered checklist, the Medline, Scopus, Web of Science and Cochrane databases were searched, including studies reporting patients affected by AO and undergone Ankle Arthrodesis (AA) using screws as exclusive fixation method. Data were harvested regarding the cohort (sample size, age, sex, etiology), the study design (type of study, level of evidence), the surgical technique (open/arthroscopic procedure, the number of screws, the use of autograft) and the final outcome (union, complication and reoperation rate) at the longest follow-up. The risk of bias was assessed using the modified Coleman Methodology Score (mCMS) was used to assess the methodological quality of studies. Three groups were built based on the type of fixation: arthrodeses fixed with 2 screws (Group 1, G1), with 3 screws (Group 2, G2), and those augmented with a lateral fibular autograft (Group 3, G3). Results: Twenty series of patients from nineteen studies (732 ankles) were selected (G1=252 ankles, G2=209, G3=271). The pooled proportion estimate revealed a similar nonunion rate in the 2-screw group as compared to the 3-screw group (6% vs 1%; p=0.43) The pooled proportion of complications appeared higher in G1 (18%) than in G2 (8%) but it was not significantly different either (p=0.27). After exclusion of 'symptomatic hardware and screw removal' the difference was still not significant (p=0.62) although it resulted lower in G1 than in G2 (3% vs 8%, respectively). The pooled proportion of nonunions (p=0.48) and complications (p=0.76) did not differ between the AA performed without or with a fibular autograft. Conclusion: Fixation of Ankle Arthrodesis using three screws as compared to two screws seems to be advantageous in terms of reduced risk of nonunion and complications, although the difference did not achieve statistical significance in this study. The use of an adjuvant lateral distal fibular autograft does not seem to significantly increase the chances of fusion as compared to a no- autograft construct. The evidence provided so far is based on retrospective and short-term follow-up studies of moderate methodological quality. Further comparative and prospective analyses are warranted to define how to achieve the best outcome in Ankle Arthrodesis stabilized using screws.

Category: Hindfoot; Ankle; Midfoot/Forefoot Introduction/Purpose: Optimization of articular joint coverage has been shown to decrease the progression of arthritic degeneration and to improve outcomes in patients with hip and shoulder pathologies. Progressive Collapsing Foot Deformity (PCFD), previously known as Adult-Acquired Flatfoot Deformity, has been demonstrated to advance with peritalar subluxation (PTS), progressively decreased articular coverage of the subtalar joint articular facets (anterior, middle, and posterior), as well as the development of sinus tarsi and subfibular impingements. Outcome assessment in PCFD has focused on improving conventional radiographic measurements such as the talus-first metatarsal angle and the hindfoot moment arm. This study aimed to evaluate improvements of PTS, subtalar joint articular coverage, and extra-articular impingement following PCFD joint-sparing surgical treatment, as well as the influence of these improvements in patient-reported outcomes. Methods: IRB-approved prospective comparative study. Adult PCFD patients that failed conservative treatment for three-months and underwent hindfoot joint-sparing surgical procedures by a single-surgeon were enrolled. Realignment soft-tissue and bony procedures performed were recorded. All patients underwent Weight Bearing CT (WBCT) preoperatively, and at the 3- and 12- months follow-up. Two observers performed traditional WBCT PCFD measurements. The foot bones were segmented, and distance measurements were performed along the entire 3D superior surface of the calcaneus, including the subtalar joint (SJ) articular facets (anterior, middle, and posterior), sinus tarsi and subfibular area. Color-coded coverage maps (CM) were calculated to grade the amount of articular joint coverage and extra-articular impingement. Patient Reported Outcomes (PROs) were recorded at all follow-up time-points. Pre- and postoperative measurements were compared by paired T-Tests/Wilcoxon and a Multivariate regression analysis was utilized to assess the influence of improvements of articular coverage and impingement in PROs. Results: Twenty patients were included (15F/5M), mean age, BMI, and follow-up of respectively 48.1 (22 to 72) years, 33.88 (23.8 to 46.8) kg/m2, and 13.2 (4 to 27) months. Significant improvements in all traditional PCFD WBCT measurements were noted postoperatively. Articular coverage (CM) of the SJ middle and anterior facets improved postoperatively by respectively 13.5% (p=0.02) and 78% (p=0.001). Similarly, improvement in sinus tarsi impingement, with a 69% decrease in sinus tarsi coverage was observed (p

Category: Other; Basic Sciences/Biologics Introduction/Purpose: Achilles tendon injuries represent one of the most common reasons of referral to orthopaedic surgeons. The purpose of this study was to determine the 50 most-cited articles on Achilles tendon pathologies in order to outline their characteristics, examine trends in publication and evaluate the correlation between citations and the quality of evidence. Methods: We searched Web of Science papers with the single keyword 'Achill*'. We identified and analyzed the top 50 most- cited articles and abstracted their characteristics. The methodological quality was assessed using the modified Coleman Methodology Score (mCMS). The correlation between the number of citations, the citation rate (citations/y), the impact factor of the journal for the year 2020 (JIF), the year of publication, the Level of Evidence (LoE), the type of study (tendon rupture, acute tendinopathy, chronic tendinopathy), the sample size and the mCMS was assessed through multiple bivariate analyses (Pearson or Spearman correlation coefficient). Results: Mean number of citations (+-SD) was 244 +- 88.8 (range, 657 to 157), with a total number of citations of 12.194 and a mean citation rate of 12.6 +- 5.4 (range, 28 to 3). The mean impact factor for the ten journals in which the 50 manuscripts were published was 5.1. The citation rate correlated with the number of citations (R=0.56, p

Category: Hindfoot; Midfoot/Forefoot Introduction/Purpose: Posterior Tibial Tendon (PTT) dysfunction is considered to play an important role in Adult Acquired Flatfoot Deformity recently renamed Progressive Collapsing Foot Deformity (PCFD). Previous flatfoot classifications are mainly based on a progressive mechanical failure of the PTT causing chronological appearance of deformities. A consensus of experts recently met and decided to remove the central place of the PTT dysfunction from the PCFD classification system. The primary objective of our study was to assess the relation between the PTT clinical status and the three-dimensional overall foot deformity. The secondary objective was to assess the relation between the degeneration of PTT at the MRI and the three- dimensional overall foot deformity. We hypothesized that the more damaged the PTT, the more severe the deformity of the foot. Methods: We retrospectively identified all symptomatic PCFD over 18 years old who consulted our center from 01/01/2019 to 12/31/2020. PCFD with concomitant (< 3 mois) clinical examination, Weight-Bearing CT (WBCT) and MRI were included. PCFD presenting with previous surgical intervention were excluded. Finally 25 PCFD were included in the analysis (19 Women, mean age 53.96+/-14.9 years, mean BMI 33.2+/-8.1 kg/m 2 ;)A PCFD presenting either a deficit on the single heel rise test or a decrease in inversion strength (superior or equal to 3/5) was classified PTT deficient. The MRI of all these PCFD were analyzed, and PTT degeneration was classified according to Deland and Rosenberg classifications. The three-dimensional overall deformity of each PCFD was assessed on WBCT by the Foot and Ankle Offset (FAO). Normality of different variables were assessed using Shapiro- Wilk test. Comparisons were performed using Student's t-test or Anova for normal, and Mann-Whitney or Kruskal-Wallis's test for non-normal variables. Results: Patients with clinically deficient PTT (13/25 PCFD, 52%) had a mean FAO of 7.75+/-3.8% whereas patients without PTT deficit (12/25 PCFD, 48%) had a mean FAO of 6.68+/-3.9%, without significant difference between groups (p=0.49). According to Deland classification, 4/25 PTT (16%) were classified grade 0, 7/25 (28%) grade 1, 4/25 (16%) grade 2, 5/25 (20%) grade 3 and 5/25 (20%) grade 4 without any significant difference between groups (p=0.36).According to Rosenberg classification, 4/25 PTT (16%) were classified type 0, 15/25 (60%) type 1, 2/25 (8%) type 2 and 4/25(16%) type 3 without any significant difference between groups (p=0.79).Seven PCFD had a FAO>10%. Among them, 42.9% had a PTT without clinical deficit and 57.1% had a PTT with little or no damage on the MRI. Nine PCFD had a FAO

Category: Hindfoot; Midfoot/Forefoot Introduction/Purpose: Peritalar subluxation (PTS) of the hindfoot is a critical finding in Progressive Collapsing Foot Deformity (PCFD). Subluxation of the middle facet and sinus tarsi recently been shown to represent essential markers of pronounced and potentially progressive deformity. Weightbearing CT (WBCT) imaging and three-dimensional (3D) distancing coverage maps (CM) allow a complete and accurate assessment of PTS markers across the entire peritalar surface. This prospective comparative study aimed to assess the effectiveness of joint-sparing realignment surgical treatment for flexible PCFD in reducing PTS and to correlate the improvement with patient-reported outcomes (PROs). We hypothesized that would significantly improve PTS markers, mainly decreasing sinus tarsi coverage/impingement and middle facet subluxation, and that this improvement would correlate with increased PROs. Methods: In this IRB-approved prospective and comparative study, we enrolled patients with flexible PCFD, no prior surgeries, and failed conservative treatment. Included females/3 males, mean age 57.2, range 37-74) underwent joint-sparing surgical realignment procedure by a single surgeon. Standing weightbearing CT (WBCT) was complete 3-months postoperatively. Following automatic bone segmentation, 3D distance maps (DMs) of the entire peritalar surface were generated, and coverage of the subtalar joint (anterior, middle, and posterior) and sinus tarsi were assessed as markers of PTS. Joint coverage was defined as the percentage of articular space where DMs were

Category: Ankle; Hindfoot; Midfoot/Forefoot; Other Introduction/Purpose: The same Consensus that proposed a new nomenclature for Flatfoot, Progressive Collapsing Foot Deformity (PCFD), also introduced a new classification system for the disease. The idea of staging was supplemented by the construction of a system combining deformity classes and its flexibilities, using clinical and radiographic signs. The capacity of the weight-bearing computed tomography (WBCT) in evaluating PCFD and all components of peritalar subluxation has been established. The objective of this study was to compare PCFD classifications performed utilizing clinical and conventional radiographs (CR) findings with classifications established using clinical and WBCT findings. We hypothesized that evaluations considering WBCT would significantly change PCFD classifications, portraying a different picture of the disease. Methods: This retrospective IRB-approved case-control diagnostic study evaluated 89 consecutive PCFD feet (84 patients) with different presentations of the disease. Three fellowship-trained foot and ankle surgeons performed chart reviews and CR evaluations, determining PCFD classifications for the studied subjects. After a two-week washout period, the sequence was randomized, and a new classification was executed using clinical data and WBCT assessment. One of the readers repeated the WBCT evaluation two weeks later for intrarater reliability purposes. Assessments included the presence or absence of classes, such as hindfoot valgus (A), midfoot abduction/sinus tarsi impingement (B), medial column instability (C), subtalar joint subluxation/subfibular impingement (D), and valgus of the ankle joint (E) as well as flexibility (1) and rigidity (2) of existing deformities. Fleiss kappa was used for interrater and Cohen's kappa for intrarater agreements. Differences between studied groups were determined by distribution comparison. Results: Mean BMI and age were 54.4 (+-17.1) and 33.6 (+-7.6) respectively. Interrater reliability was found to be moderate (0.55) and intrarater to be excellent (0.98). Evaluation using CR produced 22.8% of 1ABC, 13% of 1AC, 8,7% of 1ABCD and 7% of 2EABCD as most prevalent classifications. WBCT assessment found 31.5% of 1ABC, 11.2% of 1ABCD, 10.1% of 2ABCDE and 5.6% 1ABCDE. Class A was the most frequent component in CR (93.5%) and WBCT (94.5%). Class B had a higher prevalence in WBCT (94.38%) than in CR (71.7%) as well as Classes C (89.9% and 88.0%), D (44.9% and 29.3%) and E (31.5% and 23.9%). The percentage of combined flexible (1) and rigid (2) deformities was also higher in the WBCT evaluation (39.3% compared to 35.8%). Conclusion: As the new classification proposes the combination of different PCFD components to better support clinical decisions, proper identification of the classes is mandatory for a complete diagnosis. WBCT showed a different rate of deformity recognition, which increased the incidence of all classes, especially B (midfoot abduction/sinus tarsi impingement) and D (peritalar subluxation/subfibular impingement). An excellent intrarater agreement was found, which infers reliability of patient assessment combining clinical and WBCT evaluation. The obtained information could help providers to enhance comprehension of the disease and to supply patients with the most precise individual care.

Category: Ankle; Arthroscopy; Sports; Trauma Introduction/Purpose: Improving the diagnosis of subtle syndesmotic instability (SSI) represents one of the most challenging missions in orthopedic surgery, since undiagnosed instability frequently leads to posttraumatic ankle arthritis. Stressed conventional radiographs, ultrasonography, bilateral comparative conventional CT and MRI serve as important diagnostic tools, however, the current diagnostic gold-standard is arthroscopic assessment, an invasive surgical method. The advent of weight- bearing computed tomography (WBCT) brought hope for improved non-invasive SSI diagnosis, particularly by utilizing distal tibiofibular syndesmotic (DTFS) area and volume measurements. However, to date, no studies assessed WBCT diagnostic accuracy for chronic SSI. The purpose of this study was to prospectively evaluate the diagnostic accuracy of WBCT area and volumetric measurements in patients with suspected chronic SSI, when compared to the gold-standard arthroscopic assessment. Methods: In this IRB-approved prospective comparative study, 11 patients with suspected SSI were enrolled from July 2019 to December 2020. Patients were assessed preoperatively by bilateral standing WBCT. Raw 3D WBCT was automatically segmented by dedicated software. WBCT measurements performed: semi-automatic DTFS area (1cm proximally to tibial dome apex); DTFS volumes (1, 3 and 5cm proximally to tibial dome apex). Threshold values for WBCT abnormality were defined based on currently available data (area>105mm 2 and volumes>796mm 3 , >3062 mm 3 , and >6733 mm 3 for 1, 3 and 5cm, respectively). Subjects underwent surgical treatment including DTFS instability arthroscopic assessment, defined as positive when a 3mm diameter sphere could enter the syndesmotic incisura. Confirmed unstable cases were treated with open reduction/internal fixation. WBCT measurements sensitivity, specificity, positive and negative predictive values (PPV/NPV) and accuracy were calculated using confirmed arthroscopic instability as diagnostic gold standard. Paired t-tests/Wilcoxon analysis was used to compare measurements. P-values105mm 2 ), including 3 true positives (+WBCT/+Arthroscopy), 1 false positive (+WBCT/-Arthroscopy), 6 false negatives (-WBCT/+Arthroscopy), and 1 true negative (-WBCT/-Arthroscopy), leading to a 33.3% sensitivity, 50%, specificity, 75% PPV 75%, 14.3% NPV and 36% accuracy. When analysing WBCT DTFS volumes (1cm), 3/11 patients were found positive (>796mm 3 ), depicting 3 true positives, 0 false positives, 2 true negatives and 6 false negatives, with resultant diagnostic accuracy of: 33.3% sensitivity, 100% specificity, 100% PPV, 25% NPV 25%, and 45% accuracy. Conclusion: This is the first study to prospectively assess WBCT diagnostic accuracy of area and volume measurements in detecting chronic SSI, comparing it to arthroscopic diagnostic standard. When compared to uninjured side, DTFS area and volumetric measurements were significantly increased in injured sides of patients with suspected SSI, including medial gutter volumes, consistent with associated deltoid ligament instability. However, interestingly, we observed a diagnostic accuracy for WBCT area and volumetric measurements to be lower than initially expected. Further incorporation of additional patients, as well as introduction of an external rotational stress can potentially optimize the WBCT diagnostic accuracy for chronic SSI.

Category: Hindfoot; Ankle; Other Introduction/Purpose: The goal of this study was to describe the abnormal joint surface interaction at the ankle, hindfoot and midfoot joints in patients presenting with Pes Planovalgus (PP) using three-dimensional (3D) distance mapping on weightbearing computed tomography (WBCT) images by comparing a series of PPs to a series of normally-aligned feet. We hypothesized that in PPs joint interactions would reveal significantly increased spaces in the medial side of the ankle, hindfoot and midfoot joints. Methods: In this case-control study, ten feet (10 patients) with asymptomatic PP (cases; N=10) were compared to 10 matched- paired (by age, gender and body mass index) normally-aligned feet (10 patients) (controls; N=10). Three-dimensional models were produced from the images and distance maps representing joint surface configuration were generated for the ankle, hindfoot and midfoot joints. The distance maps for each joint were then compared between the two groups and between regions in the same group. Results: In PP patients there was a significantly increased surface-to-surface distance anteromedially at the ankle joint (+46.3%, p

Category: Ankle; Sports Introduction/Purpose: Multiple Level I meta-analyses have been led comparing traditional static vs. more recently-introduced dynamic strategies of fixation for injuries of the distal tibiofibular syndesmosis (TFS). The aim of this review was to assess their robustness and methodological quality, providing support in the choice of a treatment strategy in case of TFS injury using the highest level of evidence. Methods: In this systematic review, conducted in accordance with the PRISMA guidelines, we identified meta-analyses/systematic reviews comparing static and dynamic fixation methods after acute TFS injury. Robustness of studies was evaluated using the Fragility Index (FI) for meta-analysis and the Fragility Quotient (FQ). The risk of bias was evaluated using the Assessment of Multiple Systematic Reviews(AMSTAR) instrument. Finally, the Jadad Decision Algorithm was applied to select the study which provided the highest quality of evidence to develop recommendations for the fixation strategy of these lesions. Results: Out of 1302 records, 4 Level I meta-analyses were included in this study. Analyzing the statistically significant dichotomous outcomes, the median FI was 3.5 (IQR, 2 to 5.5; range, 1 to 9) while the median FQ was 1.9% (IQR, 1 to 3.5; range 0.35 to 4.4). In total, 37% had a FI of 2 or less and 75% of outcomes had a FI of 4 or less. According to the AMSTAR score and Jadad algorithm, the largest meta-analysis was selected as the highest evidence provided so far. Conclusion: We selected the meta-analysis by Grassi et al. as the highest quality provided so far, which found that dynamic fixation reduced complication rates and improved clinical outcomes compared to static methods of fixation. We demonstrated that meta-analyses with statistically significant dichotomous outcomes comparing dynamic and static fixation for treating injuries of the distal tibiofibular syndesmosis are fragile, with a change in less than 4 patients or less than 2% of the study population sufficient to reverse a significant outcome to nonsignificant. Based on these findings, we recommend caution when interpreting the results of these studies.

Category: Bunion; Midfoot/Forefoot Introduction/Purpose: The Distal Metatarsal Articular Angle (DMAA) has long been described as a valgus increase of the distal articular surface of the first metatarsal in Hallux Valgus (HV) deformity. Since then, several studies have reported a poor reliability of this measurement and some authors currently claim that DMAA is misinterpreted as just the rounded shape of the lateral part of the first metatarsal head reflecting pronation of the first ray and could also be biased by the first metatarsal plantarflexion angle. Our study aimed to compare the DMAA in HV and control populations after correcting, with a dedicated software, pronation and plantarflexion of the first metatarsal. We hypothesized that after correction, DMAA will be higher in the HV population, especially in juvenile cases. Methods: We performed a retrospective case-control study including 36 HV and 20 control feet. Patients under 15 or with surgery antecedent were excluded. DMAA1 was measured as initially described on X-rays by the angle between the distal articular surface and the longitudinal axis of the first metatarsal. DMAA2 was measured on Weight Bearing Computed Tomography (WBCT) without any corrections. DMAA3 was measured after correction of the first metatarsal plantarflexion in the sagittal plane. DMAA4 was measured after correction of the pronation of the first ray relative to the ground in the coronal plane using the alpha-angle. And DMAA5 after both corrections. Corrections in the coronal and sagittal planes were performed along the axis of the first metatarsal. Normality was assessed using Shapiro-Wilk tests. Comparisons were made using Student tests for normal variables and Mann-Whitney for non-normals. Correlations between age and angles were assessed by the Pearson correlation coefficient. Results: HV and Control groups were comparable on BMI (p=0.69), Age (p=0.58) and Gender (p=0.27). DMAA1 (25.9°+/-7.3 vs 7.6°+/-4.2; p

Category: Other; Hindfoot; Midfoot/Forefoot Introduction/Purpose: Identifying markers of severity and progression in Progressive Collapsing Foot Deformity (PCFD) provides surgeons with critical information, possibly aiding in the decision making along the treatment algorithm. Subtalar middle facet subluxation (MFS), the percent undercoverage of the talus in relation to its calcaneus counterpart, was recognized as a reliable marker in weight-bearing computerized tomography (WBCT) for PCFD diagnosis. The Foot and Ankle Offset (FAO), the relative position between the center of the ankle joint and the foot tripod, is a three-dimensional WBCT tool predictive of disease severity. Our objective is to assess the relationship between the amount of MFS and FAO in flexible PCFD patients. We hypothesize that MFS is a reliable assessment of disease severity and correlates with FAO. Methods: In this retrospective IRB-approved comparative study, a total of 56 individuals with PCFD (74 feet) who underwent WBCT for baseline assessment were analyzed. Two blinded fellowship-trained foot and ankle surgeons performed the measurements. MFS was executed in the coronal-plane, at the midpoint (on sagittal-plane) of the middle facet (see attached figure). Dedicated software was utilized to perform the FAO, using the most plantar voxels of the first metatarsal, fifth metatarsal, calcaneal tuberosity and centre of the ankle. Interobserver agreement was quantified for MFS and FAO using intraclass correlation coefficient (ICC). Intermethod agreement between MFS and FAO was assessed by Spearman's correlation. Bivariate linear regression analysis was used to assess the relationship between MFS and FAO. A partition prediction model and multivariate analysis were utilized to assess influence of MFS measurements on FAO values and vice versa. Results: A total of 56 patients (74 feet) were included in the study. The ICCs for interobserver reliability was 0.87 for MFS and 0.95 for FAO. In a bivariate analysis, MFS and FAO were found to be significantly and linearly correlated (P< 0.0001, R2 0.26). Foot Angle Offset = 2.22 + 0.12*Medial Facet Subluxation (%). In multivariate analysis, FAO and body mass index (BMI) were significantly correlated with MFS (

Category: Ankle; Basic Sciences/Biologics; Hindfoot; Other Introduction/Purpose: Progressive collapsing foot deformity (PCFD), formerly termed Adult-Acquired Flatfoot Deformity (AAFD), is a complex 3-dimensional (3D) deformity characterized by peritalar subluxation (PTS) of the hindfoot through the triple joint complex. PTS severity is typically measured at the posterior facet of te subtalar joint, but recent studies have called this into question and presented the middle facet as a more accurate marker of deformity. The objective of this study was to use 3D distance mapping (DM) from weightbearing computed tomography (WBCT) images to assess PTS in PCFD patients and controls across the entire peritalar suface. We hypothesized that 3D DMs would identify the middle facet as a superior marker for PTS, as well as indicate increased extra-articular sinus tarsi and subfibular inpingements in PCFD patients. Methods: In this case control study, we analyzed WBCT data of 20 consecutive patients with flexible PCFD and 10 controls. Novel 3D distance mapping (DM) technique was used to objectively characterize joint coverage across the entire peritalar surface, including both articular (anterior, middle and posterior facets of the subtalar joint) and nonarticular regions (sisus tarsi and subfibular areas). Distance maps were measured in millimeters, and colored to highlight regions of interest. Distances from 1-4mm were shown in blue to indicate expected joint interaction/extra-articular proximity, while distances under 1mm were highlighted in yellow/red indicating close bone proximity consistent with joint space narrowing (articular) or impingement (extra-articular). Joint coverage was defined as percentage of articular area with DMs

Category: Basic Sciences/Biologics; Hindfoot Introduction/Purpose: Implant-related artifact (IRA) represents an important limitation in Computed Tomography (CT) assessment of osteotomy and fracture healing, bone-implant integration, and success of fusion procedures. Metallic implants are the most used in foot and ankle surgery and are recognized as important IRA generators. Absorbable and bio-integrative (BI) implants are attractive options for bone fixation when postoperative CT imaging is likely, particularly in procedures with higher risk for nonunion. However, the literature comparing IRA with metallic and BI implants is scarce. The objective of this study was to assess the degree of IRA around metallic and BI cannulated screws. Our hypothesis was that BI implants would demonstrate significantly decreased IRA around the inserted screws. Methods: In this cadaveric/CT imaging study, 2 below-knee specimens were used. Medial displacement calcaneal osteotomy was performed through a 5-cm long lateral heel approach. Calcaneal tuberosity was displaced medially by 10mm and fixed provisionally with 2 parallel K-wires under fluoroscopic guidance. Specimens were fixed with two headless 4.0 millimeters cannulated screws, either metallic or BI. Cone-beam CT imaging of both specimens was acquired following osteotomy screw fixation (120kVp, 5.5mA, 0.25mm isotropic). Using a dedicated software, the overall dispersion of Hounsfield units (HU) in a 3D cube of 30mm edge length was assessed. Four HU lines were then traced parallel to the screws, crossing the osteotomy site. Lines 1, 2, 3 and 4 were positioned respectively: In close proximity, over, inside the cannulation and away from the implant. The HU dispersion in these lines was measured and compared between metallic and BI implanted specimens, using T-tests/Wilcoxon analysis. P-values

Category: Midfoot/Forefoot Introduction/Purpose: The etiology of hallux rigidus has been unknown. Metatarsus primus elevates (MPE), elevated first metatarsal has been controversial. Recent studies have supported significantly elevated first metatarsal in hallux rigidus patients. Bouaicha reported MPE greater than 5 mm could be a predictive factor of hallux rigidus. Lateral weightbearing radiographs has been used to evaluate MPE, However, there are limitations of conventional radiography including variation in X-ray projection angle and foot position and superimposition of metatarsals. Cheung assessed foot alignment utilizing 3D reconstructions from WBCT and concluded that hallux rigidus patients had increased MPE. Our objective was to assess MPE and anatomical characteristics in foot alignment of hallux rigidus patients compared to a control group using WBCT. This is the first study measuring MPE on WBCT. Methods: This is a single-center, retrospective study from prospectively collected data. 20 patients with hallux rigidus and WBCT data were enrolled from October 2014 to December 2020. As a control group, 20 patients with various foot and ankle pathologies were selected. Measured WBCT parameters included 1st TMT joint version, HVA, IMA, DMAA, 1st and 2nd metatarsal lengths, Foot width, Sesamoid station and rotation angle, 1st-5th Metatarsal Angle, Metatarsus adductus angle, 2nd cuneiform-2nd metatarsal angle, Talus-1st Metatarsal Angel, 1st Metatarsal-Proximal Phalanx Angle, 1st and 2nd metatarsal declination angles and ratio, and MPE. MPE was measured as a direct distance between 1st and 2nd metatarsals using a line tangential to the first metatarsal and another perpendicular line at the metadiaphyseal junction to reach second metatarsal on parasagittal view. A Cut-off value of MPE was calculated using receiver operating characteristic curve. Two investigators independently assessed each WBCT. Results: Mean age was 43.3 in control group (45% male, 55% female) and 55.9 in HR group (60% male, 40% female). Significant differences were found in several facets of foot anatomy between HR and control groups including HVA (7.57 in control vs 14.05 in HR), DMAA (3.89 vs 8.06), forefoot width (92.96 vs 95.47), 1st MT declination angle (20.17 vs 17.82), 1st/2nd MT declination ratio (83.52 vs 76.02), and MPE (3.24 mm vs 5.40 mm). MPE was significantly higher in hallux rigidus group in all three parasagittal views (unmodified, parallel to 1st metatarsal and 2nd metatarsal). Dorsal subluxation/translation of the first metatarsal was observed at 1st TMT joint in the parasagittal view of WBCT in 9 (45%) patients of hallux rigidus group suggesting sagittal instability. No patient in control group had dorsal subluxation/translation. A cut-off value of MPE was 4.56 mm with 80% sensitivity and 90% specificity. Conclusion: To evaluate MPE on WBCT, we used a new direct measurement on parasagittal views. We found a significant difference in MPE in HR. Our WBCT results are consistent with other studies using conventional radiographs. A cut-off value of WBCT MPE for diagnosis of HR was 4.56 mm in our cohort. Considering 45% patients of the HR group had dorsal subluxation/translation of first metatarsal at 1st TMT and increased HVA, Hallux rigidus may be associated with first ray instability predominantly in sagittal plane with resultant MPE with varying degree of combined coronal plane instability resulting in increased HVA.

Category: Hindfoot; Midfoot/Forefoot Introduction/Purpose: Lateral impingements, subdivided into Sinus Tarsi (STI), Talo-Fibular (TFI), and Calcaneo-Fibular (CFI) impingements, appear to be associated with the Peritalar Subluxation (PTS) component of the Progressive Collapsing Foot Deformity (PCFD). This is not yet confirmed, as the chronological place of the different types of lateral impingements in PTS is unknown. It is also unclear whether STI are associated with PTS or Midfoot Abduction. Our primary objective was to assess the amount of PTS in STI, TFI and CFI. Our secondary objective was to determine the position of STI among the PTS and Midfoot Abduction deformities. We hypothesized that STI and TFI will be associated with a lower amount of PTS than CFI and that STI will be part involved in both PTS and Midfoot Abduction deformities. Methods: A retrospective study including 72 PCFD assessed with Weight Bearing Computed Tomography (WBCT) was realized. Patients under 15 or with a previous history of surgery were excluded. Lateral impingements were assessed on WBCT images and subdivided as STI, TFI and CFI. Both direct and indirect signs of impingement were considered positive. The amount of PTS was assessed by the percentage of uncoverage and the incongruence angle of the Middle Facet (MF). Midfoot-Abduction was assessed by Talonavicular coverage angle and global foot deformity by Foot and Ankle Offset (FAO). These data were collected by two independent observers and one performed a blinded second assessment. Interobserver and Intraobserver reliabilities were determined using unweighted Cohen's kappa values for lateral impingements and using intraclass correlation coefficients for the measurements. Impingement groups were compared using Student's T-tests for normal, and Mann-Whitney for non-normal variables. Results: Interobserver and Intraobserver reliabilities ranged from substantial to almost perfect for all assessments. STI was present in 84.7%, TFI in 65.2% and CFI in 19.4% of PCFD cases. PCFD with STI showed significant increases of MF uncoverage (p=0.0001), FAO (p=0.0008) and Talonavicular coverage angle (p=0.0197) compared to PCFD without STI. PCFD with TFI did not show significant difference on measurements compared to PCFD without TFI. PCFD with CFI had associated STI in 100% and TFI in 64.2% of cases. PCFD with CFI showed significant decreases of MF incongruence (p=0.0398) and significant higher FAO (p=0.0058) compared to PCFD without CFI. PCFD with both STI and CFI showed significant decreases of MF incongruence (p=0.032) and significant higher FAO (p=0.028) compared to PCFD with isolated STI. Conclusion: Our hypotheses have not been confirmed. STI was associated with both PTS and Midfoot Abduction deformities but neither TFI nor CFI were associated with PTS considering MF subluxation. Conversely, CFI was associated with a reduction of the MF incongruence angle despite being associated with a higher global deformity. STI may be associated with earlier PCFD with a concentration of the malignment forces in the subtalar joint whereas CFI may occur later and be associated with a failure of the deep layer of the deltoid ligament and a talar tilt. This could explain the relative reduction of the PTS in CFI.

Category: Midfoot/Forefoot Introduction/Purpose: Medial column instability (MCI) in Progressive Collapsing Foot Deformity (PCFD) is not solely determined by forefoot varus (FV). First ray hypermobility, hallux valgus, midfoot arthritis, gapping at the tarsometatarsal joint and dorsal metatarsal migration are findings associated with MCI. Acknowledgement of this instability requires inclusion of a procedure to the medial column in order to correct the forefoot varus, stabilize the ray and bring the foot to a plantigrade tripod position. Cotton opening wedge medial cuneiform osteotomy and Lapidus tarsometatarsal arthrodesis are procedures of choice in these scenarios. We have combined these 2 procedures into one called Lapicotton. The purpose of this study was to present the short-term outcomes of this technique.We hypothesized that Lapicotton will improve both clinical and radiological outcomes. Methods: We performed an IRB-approved retrospective study comprising 3 PCFDs having benefited from a Lapicotton procedure. Clinical outcomes were assessed with the European Foot and Ankle Society Score (EFAS), the Foot Function Index Score (FFI) and the Pain Catastrophizing Scale (PCS). Radiographic outcomes were assessed using weight-bearing computed tomography (WBCT) assessments. Middle Cuneiform Floor distance, Forefoot Arch Angle, Middle Facet uncoverage percentage, Talonavicular Coverage angle and the Foot and Ankle Offset (FAO) were measured. All these data were both preoperatively and postoperatively collected. Comparison between preoperative and postoperative results were done as described below. The Kruskal-Wallis H-test for independent groups was used to compare median values of the EFAS. The Wilcoxon signed-rank test for paired samples was used to compare preoperative and postoperative variables of FFI and PCS. For the radiographic measurements, normality was assessed using Shapiro-Wilk test. Comparisons were made using Student tests for normal variables and Mann-Whitney for non-normals. Results: This small series included 2 female and 1 male, with a mean age of 56 and a mean BMI of 31.8 kg/m 2 . Mean follow up was 2.9+/-0.2 (range from 2.7 to 3.1) months. 2 out of 3 patients simultaneously benefited of a Medial Calcaneal Displacement Osteotomy (MDCO 10mm) and a Lateral Column Lengthening (LCL 8mm). The wedge sizes used for the Lapicotton were 8 mm in all cases. Regarding clinical outcomes, EFAS (p=0.79) and FFI (p=0.99) did not showed any significant improvement whereas PCS were significantly improved (Δ=-5.67[-9.2–2.2];p=0.03). Regarding radiological outcomes, fusion was present in all the cases at the maximal follow-up. Middle cuneiform floor distance and Forefoot Arch Angle were significantly increase (respectively Δ=6.9;CI95%=[6.4;7.4];p< 0.01 and Δ=7.5;CI95%=[4.3;10.8]p

Category: Ankle; Hindfoot; Other Introduction/Purpose: Peritalar subluxation (PTS) of the hindfoot is a critical finding in Progressive Collapsing Foot Deformity (PCFD). Subluxation of the middle facet and sinus tarsi impingement have recently been shown to represent essential markers of pronounced and potentially progressive deformity. Weightbearing CT (WBCT) imaging and three-dimensional (3D) distance (DM) and coverage maps (CM) allow a complete and accurate assessment of PTS markers across the entire peritalar surface. This prospective comparative study aimed to assess the effectiveness of joint-sparing realignment surgical treatment for flexible PCFD in reducing PTS and to correlate the improvement with patient-reported outcomes (PROs). We hypothesized that surgical treatment would significantly improve PTS markers, mainly decreasing sinus tarsi coverage/impingement and middle facet subluxation, and that this improvement would correlate with increased PROs. Methods: In this IRB-approved prospective and comparative study, we enrolled patients with flexible PCFD, no prior surgeries, and failed conservative treatment. Included patients (n=10, 7 females/3 males, mean age 57.2, range 37-74) underwent joint-sparing surgical realignment procedure by a single surgeon. Standing weightbearing CT (WBCT) was completed preoperatively and 3- months postoperatively. Following automatic bone segmentation, 3D distance maps (DMs) of the entire peritalar surface were generated, and coverage of the subtalar joint articular facets (anterior, middle, and posterior) and sinus tarsi were assessed as markers of PTS. Joint coverage was defined as the percentage of articular space where DMs were

Category: Ankle; Sports Introduction/Purpose: Lateral ankle sprains are the most frequent ankle trauma and may lead to chronic lateral ankle instability (CLAI). Studies have reported anterior talofibular (ATFL) and calcaneofibular (CFL) ligaments tensile strengths around 200N and 300N. Cone Beam Weight Bearing CT (WBCT) allows visualization of 3D bony anatomy in different functional positions. The primary objective of this study was to calculate 3D ATFL and CFL tensile loads in patients diagnosed with CLAI performing Forced Inversion stance during WBCT imaging (FI-WBCT) and wearing shoes, and to compare them with a population of non-CLAI ankles. The secondary objective was to evaluate the relative contribution of shoes. We hypothesized that ATFL and CFL calculated tensile loads (CTLs) would be close to previously published data with minimal contribution of shoes. Methods: This retrospective comparative Level III study included 20 CLAI ankles and 20 controls with known demographics and available FI-WBCT datasets. Patients under 18 or with a previous history of trauma or surgery which could affect ankle architecture were excluded. A mechanical lever arm model was calculated for each case using the spatial coordinates of the weight bearing surfaces of the shoe and foot (bony landmarks: 5th metatarsal head, base and calcaneus lowest points, distal tip of the medial malleolus, ATFL and CFL distal insertion points, distal tip of the fibula). The ATFL and CFL CTL were calculated respectively as the coronal force applied at the distal insertion landmarks of the ATFL on the talus and CFL on the calcaneus. Normality was assessed using the Shapiro-Wilk test, then variables were compared using the Student t-test (normally-distributed) or the Wilcoxon rank sum test (non normally-distributed variables). Chi-2 was used for categorical variables. Results: Mean age [42.4+-10.9 vs 40.8+-10.7 years; p=0.317], Body Mass Index [24.4+-3.3 vs 24.9+-4 kg.m-2; p=0.34], sex (p=0.75), side (p=0.75) and foot alignment (FAO -1.05%+-5.5 vs 0.08%+-3.6; p=0.22) were not different between CLAI ankles and controls. CTLs for ATFL were 194N+-149 in CLAI and 192N+-183 in controls (p=0.85), while for CFL they were 311N+-286 and 311N+-361, respectively (p=0.79). Using footwears, CTLs were 406N+-360 in CLAI vs 608N+-380 in controls (p

Category: Basic Sciences/Biologics; Hindfoot; Midfoot/Forefoot Introduction/Purpose: Progressive collapsing foot deformity (PCFD), formerly termed Adult-Acquired Flatfoot Deformity (AAFD), is a complex 3D deformity characterized by peritalar subluxation (PTS) of the hindfoot through the triple joint complex. In this context, adjacent structures may adopt different positions and boney relations can change, producing areas increased contact or subluxation. The objective of this study was to use 3D distance maps (DMs) and coverage maps (CMs) from weightbearing CT (WBCT) images to assess subluxation across the Chopart joint in PCFD patients. We hypothesized that CMs would show decreased coverage indicative of subluxation through certain regions of the Chopart joint in PCFD patients when compared to the controls. Methods: In this IRB-approved, retrospective case-control study, we analyzed WBCT data of 18 consecutive patients with flexible PCFD and 10 controls. Using principle component analysis, candidate coverage area was divided into nine regions on the talar head and 4 regions on the calcaneal-cuboid (CC) articular surface. Novel 3D distance mapping (DM) technique was used to objectively characterize joint coverage across the entire Chopart joint surface on both the talus and calcaneus. Distance maps were measured in millimeters and colored to highlight covered areas. Areas with distances less than 4mm were defined to be covered, while areas with distances greater than 4mm were considered to be uncovered. Joint coverage was defined as percentage of articular area with DMs lower than 4 mm. Coverage Maps (CM) were created to highlight areas of coverage (teal) versus non- coverage (pink). Comparisons were performed with independent t-tests, assuming unequal variances. P values

Category: Ankle; Hindfoot; Midfoot/Forefoot Introduction/Purpose: The cavovarus configuration sets the grounds for various pathological conditions, often involving the arthritic degeneration of the medial column. The objective of this study was to analyze the joint surface interaction at the ankle, hindfoot and midfoot joints using distance mapping on WBCT images in a series of cavovarus feet and compare them to normally aligned feet. Methods: In this case-control study, a database containing WBCT datasets from 370 feet (189 patients) obtained in a specialized foot and ankle unit from July 2016 to October 2018 was used. Ten feet (10 patients) with asymptomatic cavovarus shape were extracted (cases group; N= 10) and compared to 10 matched-paired (by age, gender and body mass index) normally aligned feet (10 patients) (controls group; N=10). Colored distance maps were generated for the ankle, hindfoot and midfoot joints and divided in zones, therefore differences were assessed between the two groups. Results: In the cavovarus group there was a significant increase in surface-to-surface distance at the posterior tibiotalar joint and a reduced distance at the anterior part, together with a greater distance at the posterior half of the medial gutter. Also, a decrease in surface-to-surface distance on the anterior half of the anterior facet and an increased distance on the posterior quadrants of the posterior facet of the subtalar joint were found. At the sinus tarsi, the lateral aspect of the talonavicular joint, the naviculocuneiform and the tarsometatarsal joints there was a statistically significant increase in surface-to-surface distance in cavovarus patients as compared to controls. Conclusion: In this study, the use of distance mapping analysis on WBCT images enabled to identify significant differences in surface-to-surface interaction at the foot and ankle joints between cavovarus and normally-aligned feet.

Category: Bunion; Midfoot/Forefoot Introduction/Purpose: Rotational deformities of the first ray have been described as essential components of hallux valgus (HV) deformity, influencing its severity and progression. The exact deformity location along the medial column, as well as the typical rotational pattern of each bone, is yet to be fully understood. The objective of this study was to evaluate the rotational position of the navicular, medial cuneiform, first metatarsal and proximal phalanx using three-dimensional weightbearing CT (WBCT) images of a diversity of patients with foot pathologies. Our goal was to describe the rotational profile of medial column bones, serving as a reference for future studies. Methods: A retrospective review of patients that underwent WBCT assessment of multiple foot and ankle pathologies was conducted in a single Institution. A blinded and independent Fellowship-Trained Foot and Ankle Orthopedic Surgeon performed measurements in Multiplanar Reconstruction (MPR) WBCT images assessing the rotational profile of each bone of the medial column (navicular, medial cuneiform, first metatarsal and proximal phalanx of the great toe), as demonstrated in the attached figure. The first metatarsal, representing a long bone, was evaluated on its proximal and distal ends. A total of 110 patients were included. As standard, we considered pronation as positive values and supination as negative values. Comparisons were performed using independent t-tests or Wilcoxon tests. P-values of

Category: Hindfoot; Other Introduction/Purpose: Adult Acquired Flatfoot Deformity (AAFD) results in progressive foot collapse through peritalar subluxation. Numerous radiographic and Weight Bearing CT (WBCT) measurements have been described in the literature aiming to gauge the severity of the multiple components of the deformity. However, the real diagnostic power of each measurement is currently unknown. Moreover, novel measurements have recently been described such as 3D biometrics and multidimensional measurements. The objective of this case-control study was to individually assess the diagnostic accuracy of known 2D and 3D WBCT measurements and to compare it with a novel multidimensional measurement. We hypothesized that the latter would demonstrate superior diagnostic power than isolated 2D and 3D measurements. Methods: Retrospective case-control study, including 19 AAFD feet and 19 controls that were matched for age, gender and BMI (9 male, 10 female, mean age 54.4 years in both groups). All patients had standing WBCT imaging as baseline assessment of their foot pathology. 2D measurements assessed included: axial and sagittal talus-first metatarsal angles (TM1A), talonavicular coverage angle (TNCA), forefoot arch angle (FFAA) and middle facet incongruence angle (MF°) and uncoverage percentage (MF%). The 3D Foot and Ankle Offset (FAO) was calculated using semi-automatic software. A novel multiplanar biometric measurement (AAFD- MD) was calculated using a multidimensional mathematical algorithm that pooled multiplanar 2D measurements. Intra and interobserver reliabilities were assessed. Comparisons between variables were done using Student-t test or Wilcoxon rank-sum test. Receiver Operating Characteristic (ROC) curves were calculated to determine diagnostic accuracy, sensitivity and specificity of each measurement. Results: AUC for ROC curves were 1. for MF%, 0.96 for FAO, 0.94 for MF° and 0.92 for AAFD-MD. For MF%, a threshold value equal of greater than 28.1% was found to be diagnostic of AAFD with a sensitivity of 100% and specificity of 100%. FFAA were decreased in AAFD: 6.3° versus 15.2° in controls (p

Category: Bunion; Other Introduction/Purpose: Cone Beam Weight Bearing CT (WBCT) is gaining traction, particularly in the foot and ankle, due to the ability to perform natural stance weight bearing 3D scans. However, the resulting wealth of 3D data renders daily clinical use time consuming. Therefore, reliable automatic measurements are indispensable in order to make best use of the technology. The aim of this study was to evaluate a beta-version WBCT artificial intelligence (AI) automatic measurement system for the M1-M2 intermetatarsal angle (IMA), which is applicable in the absence of metallic hardware in the foot and ankle. We hypothesized that automatic measurements would correlate well with human measurements, and that software reproducibility would be better and close to perfect compared to manual measurements. Methods: In this retrospective case-control study, 90 feet were included from patients who underwent WBCT scans during routine follow up: 44 feet (90.9% female, mean age 54 years) with symptomatic hallux valgus (HV), 46 controls (76.1% female, mean age 49 years). Patients were excluded if they had history of surgery or trauma involving the first or second metatarsals, hallux rigidus, or presence of metal in their foot/ankle. IMA was measured manually on Digitally Reconstructed Radiographs (DRR IMA) and automatically with AI software producing auto 2D (ground plane projection) and 3D (multiplanar) measurements. Each IMA DRR was measured by two independent raters twice to calculate intraclass correlation coefficients (ICCs). To assess intra- software reliability, AI software measurements were made twice on each dataset. Manual and automatic measurements were compared between HV and control groups. Failures of the AI software to produce a measurement were recorded. Results: Mean values for controls were 8.6° +-1.8° (range, 5°-14°) for the manually measured DRR IMA, 9.3° +-2.8° (range, 3°- 17°) for auto 2D, and 9.2° +-2.6° (range, 3°-16°) for auto 3D IMA measurements. Compared to controls, HV patients demonstrated significantly increased IMA (p

Category: Bunion; Midfoot/Forefoot Introduction/Purpose: Hallux Valgus (HV) is a complex 3D deformity. Coronal rotation of the first column has been advocated as a key component of its pathophysiology. Cone Beam Weightbearing CT (CB-WBCT) provides 3D images of the foot and ankle bones under physiological load and may provide any absolute or relative measurements. However, the fact that numerous bones and joints are concerned makes analysis time-consuming and results difficult to render and interpret. Artificial Intelligence based Automatic Segmentation (AIAS) is a new tool which allows for volumetric identification and localization of bones. The objective of this study was to use this tool to obtain exhaustive measurements of the whole first column relative to the second and third columns in HV and compare them to the normal population. Methods: Retrospective comparative, level III study including 16 HV cases and 16 controls matched for age, sex and BMI. Bilateral CB-WBCT images performed as standard care were available for each patient. Inclusion criteria were clinically identified HV cases with first intermetatarsal angle (IMA) >10° and HV angles (HVA) >15° as measured on digitally reconstructed radiographs. Patients under 18 years of age, history of trauma or surgery resulting in a potential modification of the forefoot were excluded. Datasets were analyzed using AIAS software which provided: 3D coordinates for spatial position and orientation and angles of the first, second and third metatarsals and cuneiforms, sesamoids, first phalanx of the first ray, navicular, talus, calcaneus. Normality was assessed using a Shapiro-Wilk test and differences between means were calculated using Welch’s unequal variances t-test. Results:: Mean age and BMI were respectively 57.25 +- 9.65 years and 22.23 +- 2.85 kg.m2; 93.75% (31/32) feet came from women. The mean IMA was 12.9° +- 3° in HV and 8.7° +- 1.4° in controls. In the axial plane, the following measurements were found to be significantly different: IMA (p

Category: Hindfoot; Ankle; Other Introduction/Purpose: Semi-automatic three-dimensional (3D) biometric weightbearing CT (WBCT) tools have been shown to accurately demonstrate the relationship between the center of the ankle joint and the tripod of the foot. The measurement of the Foot and Ankle Offset (FAO) represents an optimized biomechanical assessment of foot alignment. The objective of this study was to evaluate the correlation between FAO and traditional adult acquired flatfoot deformity (AAFD) markers, measured in different planes. We hypothesized that the FAO would significantly correlate with other radiographic markers of pronounced AAFD. Methods: In this retrospective comparative study, we included 113 patients with stage II AAFD, 43 men and 70 women, mean age of 53.5 (range, 20 to 86) years. Three-dimensional coordinates (X, Y and Z planes) of the foot tripod (most plantar voxel of the first and fifth metatarsal heads, and calcaneal tuberosity) and the center of the ankle joint (most proximal and central voxel of the talar dome) were harvested by two blinded and independent fellowship-trained orthopedic foot and ankle surgeons. The FAO was automatically calculated using the 3D coordinates by dedicated software. Multiple WBCT parameters related to the severity of the deformity in the coronal, sagittal, and transverse plane were manually measured. Results: We found overall good to excellent intra (range, 0.84-0.99) and interobserver reliability (range, 0.71-0.96) for manual AAFD measurements. FAO semi-automatic measurements demonstrated excellent intra (0.99) and interobserver reliabilities (0.98). Hindfoot moment arm (p

Category: Hindfoot; Ankle; Other Introduction/Purpose: Adult acquired flatfoot deformity (AAFD) is a three-dimensional (3D) and complex pathology that is characterized by peritalar subluxation (PTS) of the hindfoot. Measuring the amount of subluxation of the subtalar joint at the posterior facet was described and utilized for many years as a marker of PTS. The subluxation of the middle facet was recently proposed as possibly a more accurate and reliable early marker of pronounced deformity, with almost 100% sensitivity and specificity for symptomatic AAFD. The objective of this study was to compare the amount of subluxation of both the medial and posterior facets in patients with increased hindfoot valgus and controls. Methods: In this IRB-approved retrospective comparative study, we included a total of 91 patients with AAFD (108 feet) who underwent standing weightbearing CT (WBCT) as a standard baseline assessment of their foot deformity. One blinded Fellowship- Trained Orthopedic Foot and Ankle Surgeon with more than 10 years of experience performed WBCT measurements regarding the amount of subluxation of the subtalar joint (percentage of uncoverage) at the posterior and middle facet, as previously described in the literature (Please see attached Figure). Measurements were performed at the sagittal midpoint of the articular facets using Coronal Plane WBCT images. The inter-method agreement between the posterior and middle facet subluxation was assessed using Spearman’s Correlation and Bivariate Analysis. A paired comparison of the measurements was performed using Wilcoxon. P-values of

Category: Hindfoot; Ankle; Ankle Arthritis; Sports Introduction/Purpose: Severe hindfoot valgus deformity has been reported as one of the main causes of sinus tarsi and subfibular impingement in patients with adult acquired foot deformity (AAFD). Chronic Impingement and overload of the talus and/or calcaneus on the articular surface of the distal fibula can potentially lead to distraction stresses on the distal tibiofibular syndesmosis (DTFS). However, to the authors knowledge, no direct assessment of DTFS widening in patients with AAFD has been reported in the literature. The purpose of this study was to evaluate the correlation between hindfoot alignment and DTFS widening using weightbearing computed tomography (WBCT) images, and to compare the results between AAFD patients and controls. Methods: In this case-control study, we included 97 patients who underwent WBCT examination, 63 AAFD patients and 34 controls, with no history of major ankle trauma or surgeries of the foot and ankle. Hindfoot alignment was assessed using Foot and Ankle Offset (FAO) and the widening of the DTFS was evaluated by measuring the syndesmotic area (mm2) on axial plane WBCT images, at a level 1cm proximal to the apex of the tibial plafond. Controls were defined as patients with no clinical AAFD and normal FAO values (from -0.6 to 5.2). FAO and DTFS area measurements were compared by paired T-tests and ANOVA. Correlation between variables was assessed by bivariate linear regression. A partition predictive model was used to define threshold values of FAO that would influence DTFS area measurements. P-values of less than 0.05 were considered significant. Results: AAFD patients demonstrated significantly increased mean values for DTFS area (90.0mm2; 95%CI, 84.3 to 95.7) when compared to controls (79.9 mm2; 95%CI 73.8 to 85.9), p=0.03. However, no significant direct linear correlation was found between FAO and DTFS area measurements (p=0.07) in the bivariate analysis. The partition predictive model demonstrated that two threshold values of FAO would significantly influence DTFS area (R2=0.14): when FAO was 7, the mean DTFS area was 92.7mm2 (SD 22.4). Interestingly, when assessing patients with more severe valgus (FAO>7), the DTFS area measurements were even higher when FAO values were in between 7 and 9.3 (average, 104.6mm2, SD 22.5), but decreased when FAO>9.3 (average, 88 mm2; SD 22.3). Conclusion: This is the first study to compare distal tibiofibular syndesmotic widening in patients with AAFD and controls. We found that AAFD patients had significant syndesmotic widening when compared to controls, with a difference of about 10 mm2 in the measured area. More than that, we found that AAFD patients with FAO in between 7 and 9.3 would demonstrate the largest amount of syndesmotic widening. However, no direct linear correlation was found between FAO and syndesmotic area measurements. Our findings suggest that increased hindfoot valgus deformity may have negative biomechanical impact on syndesmotic alignment, with increased stresses and resultant widening.

Category: Hindfoot; Midfoot/Forefoot; Other Introduction/Purpose: Recent literature has established the middle facet of the subtalar joint as a reliable and accurate marker of pronounced peritalar subluxation (PTS) in Adult Acquired Flatfoot Deformity (AAFD) patients. The Foot and Ankle Offset (FAO) has also been accepted as a more complete and three-dimensional (3D) measurement of foot collapse and hindfoot valgus. To date, no assessment has been made regarding the relationship between the severity of the AAFD and the amount PTS measured at the middle facet. The objective of this study was to investigate the correlation between these variables. We hypothesized that direct positive linear correlation would be found, with significantly increased middle facet joint incongruence and subluxation in patients with more pronounced hindfoot valgus and foot collapse. Methods: In this IRB-approved retrospective comparative study, we included 76 feet (42 left, 35 right) with symptomatic AAFD who underwent standing weightbearing CT (WBCT) as standard baseline assessment of their foot deformity. One blinded fellowship-trained foot and ankle surgeon with more than 10 years of experience performed measurements using multiplanar reconstruction (MPR) WBCT images. Manual measurements of subluxation and incongruence of the middle facet were performed at the anteroposterior midpoint of the articular facet. Semiautomatic calculation of the FAO was performed after 3D coordinate harvesting of the weightbearing points of the first, fifth metatarsal and calcaneus as well as the center of the ankle. Correlation of FAO severity and subluxation/incongruence of the middle facet was assessed by Spearman’s correlation and bivariate analysis. Paired Wilcoxon was utilized to compare FAO values in congruent (0% subluxation), subluxated (1-99% subluxation) and dislocated middle facets. P-values 20) (p

Category: Ankle; Ankle Arthritis; Bunion; Hindfoot; Midfoot/Forefoot; Other Introduction/Purpose: The analysis of the hindfoot alignment (HA) is important in the management of various foot and ankle pathologies. Foot Ankle Offset (FAO), measured using Weight Bearing CT (WBCT) scans is a 3D biometric measurement of HA described in the literature, however only with relation to the clinical morphology of the hindfoot or previously known 2D biometrics such as the hindfoot angle. The aim of this study was to observe the FAO distribution on a continuous, large population of patients and to analyze its discriminating power between pathological and non-pathological cases. We hypothesized that threshold values could be determined for the normal range of FAO in terms of risk of presenting with different pathologies in varus or valgus configurations. Methods: Prospective, IRB approved (COS-RGDS-2016-06-008-P-LINTZ-F, Clinical Trials NCT 04134962), level II study. 125 patients (250 feet) with bilateral WBCT as standard follow-up were included at a single institution. Mean age was 54 years (18-84), 58.4 % were female. Each patient was clinically evaluated, scans analyzed by a fellowship-trained foot and ankle surgeon and all degenerative pathologies classified depending on their anatomical location (medial or lateral). HA was measured using FAO on 3D datasets and Tibio-Calcaneal Angle (TCA) on 2D Saltzman-El-Khoury views. All scans were analyzed a second time by a radiology MD. FAO and TCA Intraclass Correlation Coefficient (ICCs) and Spearman’s correlation coefficient were calculated. Mean FAO values were calculated for all, normal, varus and valgus cases, and each pathology group. Receiver operating Curves (ROC), threshold values of FAO and area under the curve (AUC) were established for predicting an increased risk of medial or lateral pathologies. Results: A threshold FAO value of -1.64% was found to best predict the risk of lateral pathology (51.4% sensitivity, 85.1% specificity, AUC=0.72) and 2.71% (95% sensitivity, 82.8% specificity, AUC=0.93) for medial pathology, both versus no pathology. Mean FAO value was 1.65% +-4.72% and mean TCA was 4.15° +-7.67°. Interobserver reproducibility for FAO and TCA was respectively 0.96 [95% CI 0.95-0.97] and 0.95 [95% CI 0.94-0.96]. Spearman’s correlation coefficient between FAO and TCA was 0.697. Clinical assessment rated 167 feet as normal, 33 varus, and 50 valgus. Mean FAO values were respectively 0.99 +-3.26%, - 2.53+-5.05 % and 6.81+-2.70%. We found that the mean FAO was 0.42+-3.19 % for non-pathologic feet, -2.30+-4.58 for lateral pathologies, 6.62+-2.77 for medial pathologies. Conclusion: The most important finding in this prospective clinical trial is the description of normal HA as the FAO range in which the risk for degenerative Foot and Ankle pathology is the least: -1.64% to 2.71%. This new, pathology based prognostic approach to HA is different to the traditional morphological approach. The potential of WBCT to provide computerized, data- based and biomechanically meaningful 3D measurement tools could improve the prognostic potential of biometrics such as HA. Results will be refined in the future by increasing the size of study population.

Category: Ankle; Hindfoot; Other Introduction/Purpose: Adult acquired flatfoot deformity (AAFD) is a complex deformity. Previous work has demonstrated correlation between postoperative foot alignment and patient-reported outcomes. While this work has provided essential targets for surgeons performing flatfoot reconstruction, there is an absence of data that would enable surgeons to predict which patients are likely to have greater or less improvement after surgery based on their preoperative deformity. Conventional radiographs alone may not provide enough detail to isolate individual elements of the deformity. Weightbearing CT (WBCT) allows for far more precise analysis in this regard. We hypothesized that there would be a set of parameters defining preoperative alignment on WBCT that would predict which patients are at risk for a lower magnitude of postoperative improvement in patient-reported outcomes (PROs). Methods: In this retrospective IRB-approved study, patients that underwent surgical flatfoot reconstruction after having a preoperative standing WBCT were identified. Preoperative WBCT images were evaluated by two independent/blinded observers. Multiple parameters related to preoperative alignment and AAFD severity were measured in the sagittal, coronal and transverse planes. Parameters measured included talus-first metatarsal angle; distances between the floor and the navicular, medial cuneiform and cuboid; subtalar joint horizontal angle; superior talar - inferior talar angle; subtalar joint subluxation; talonavicular uncoverage angle; hindfoot moment arm (HMA); and foot and ankle offset (FAO). Prospectively collected data regarding preoperative and postoperative PROs was evaluated. Six PROs components were assessed: physical function; pain interference, pain intensity, global mental health, global physical health and depression. Multivariate regression analysis and a partition prediction model were used to assess the correlation between preoperative alignment and improvement in PROs. P-values of less than 0.05 were considered significant. Results: A total of 51 patients with a preoperative WBCT and postoperative PROs scores were identified and included. Demographic data is shown in Table 1. Multivariate regression analysis demonstrated that preoperative alignment significantly correlated with improvement in three out six components of PROs: pain interference, pain intensity and global mental health. The strongest predictor of improvement in PROMIS physical function t-score was medial cuneiform to floor distance, for pain interference t-score: cuboid to floor distance, for pain intensity: subtalar joint subluxation, for depression t-score: superior talar - inferior talar angle, and for global physical and mental health t-scores: sagittal talus-first metatarsal angle. Conclusion: Our analysis yielded readily identifiable cutoffs for WBCT measurements, where values above or below were correlated with significant differences in the magnitude of PRO score change. Interestingly, measures of sagittal plane collapse and hindfoot valgus were the most predictive of score changes. This data provides useful information for surgeons counseling patients prior to flatfoot reconstruction. Future work using this data to develop prediction models for postoperative outcomes would be valuable, as would studies using WBCT to evaluate the relationship between postoperative corrected alignment and PROs. Complete results are shown in the attached Table.

Category: Ankle Arthritis; Ankle; Hindfoot; Other Introduction/Purpose: Sinus tarsi and Subfibular impingement are considered the main causes of lateral foot pain in patients with Adult Acquired Flatfoot Deformity (AAFD). They are considered important markers in the spectrum of progressive peritalar subluxation (PTS) in patients with AAFD. Recent literature has also highlighted the use of the Middle Facet of the subtalar joint as a more accurate indicator of PTS. The objective of this study was to assess the relationship between lateral impingement and middle facet PTS. Our hypotheses were that patients with sinus tarsi and subfibular impingement would demonstrate more severe PTS than patients with no impingement, and that subfibular impingement would represent a better indicator of pronounced deformity when compared to sinus tarsi impingement. Methods: In this retrospective comparative Cohort Study, we included 110 AAFD patients that underwent standing weightbearing CT (WBCT) as a standard baseline assessment of their foot deformity. The presence or absence of sinus tarsi and subfibular impingements, as well as the incongruence angle and percentage of subluxation of the middle facet of the subtalar joint, were manually measured on multiplanar reconstruction (MPR) WBCT images by a blinded fellowship-trained foot and ankle surgeon. Descriptive statistics were used to describe the rate of sinus tarsi and subfibular impingement as well as mean values for middle facet incongruence angle and subluxation. Wilcoxon test was used to compare the values of PTS at the middle facet in patients with or without sins tarsi and subfibular impingement. A partition prediction model was used to assess the values of middle facet PTS that would foresee a higher risk for lateral impingement. P-values

Category: Hindfoot; Ankle; Midfoot/Forefoot Introduction/Purpose: Multiple surgical techniques are used in the correction of Adult Acquired Flatfoot Deformity (AAFD). Assessment of the efficacy of a surgical treatment in the correction of the deformity is usually performed by clinical evaluation and conventional radiographic imaging. Weightbearing CT (WBCT) allows a more reliable and multiplanar evaluation of AAFD. The Foot and Ankle Offset (FAO) is a WBCT biometric semi-automatic measurement that gauges the relative positioning between the foot tripod and the center of the ankle joint. This study aimed to investigate the efficacy of surgical treatment in correcting AAFD, comparing preoperative and postoperative FAO measurements. We hypothesized that surgical treatment would provide significant correction of the deformity, centering the tripod of the foot underneath the ankle joint. Methods: In this prospective comparative study, 21 adult patients (22 feet) with flexible AAFD were included, mean age 55 (range, 23-81) years, 13 females and eight males. Patients underwent preoperative and postoperative standing WBCT examination. Three-dimensional coordinates (X, Y and Z planes) of the foot tripod (weightbearing point of the first and fifth metatarsals and calcaneal tuberosity) and center of the ankle (apex of the talar dome) were harvested by two independent and blinded observers. The FAO was automatically calculated from the harvested 3D coordinates by dedicated software. Data regarding the surgical technique used was recorded. Patient Reported Outcomes (PROs) were collected preoperatively and postoperatively at a mean follow-up of 22 (range, 8-36) months. Pre and postoperative FAO measurements were compared by paired T-tests. Multivariate analysis was used to assess the influence of surgical procedures in the amount of FAO correction. P-values of less than 0.05 were considered significant. Results: We found excellent intra (0.98) and interobserver reliability (0.96) for FAO measurements. The mean preoperative FAO was 10.4 (95% CI, 8.5 to 12.1). There was a significant correction of the deformity postoperatively (p

Category: Ankle; Ankle Arthritis; Arthroscopy; Sports Introduction/Purpose: Chronic subtle distal tibiofibular syndesmotic instability (DTFSI) is relatively common, and consequences of undiagnosed injuries can be devastating. Diagnosing acute and chronic injuries is challenging, and the most commonly used diagnostic tools are physical exams, conventional radiographs and bilateral CT, and MRI. Arthroscopic assessment, an invasive method, is currently considered the gold standard. Weightbearing CT has just emerged as an excellent dynamic non-invasive diagnostic test. Recent literature highlighted the accuracy of syndesmotic incisura area measurements in diagnosing subtle DTFSI. The aim of our study was to develop and validate the use of a novel automatic 3D volumetric assessment of the incisura, and to compare the measurements between patients with surgically confirmed DTFSI and controls. Methods: In this IRB-approved case-control study, patients with suspected unilateral chronic subtle DTFSI underwent bilateral standing weightbearing CT (WBCT) examination before surgical treatment. DTFSI was confirmed by arthroscopic assessment. We also included control patients that underwent WBCT tests for forefoot related problems and no history of syndesmotic injuries. The syndesmotic incisura volume (mm3) was measured starting at the level of the ankle joint to two proximal points, 10 and 15mm proximally to the joint. A 3D automatic measurement algorithm composed of automated segmentation of the distal tibia and fibula and recognition of the incisura volume based on Hounsfield units (HU) assessment was performed. Measurements were compared between DTFSI patients and controls. A partition prediction model, ROC curves and area under the curve (AUC) were performed to assess the diagnostic accuracy of the automatic volumetric analysis to detect DTFSI. P-values of less than 0.05 were considered significant. Results: In this preliminary report, four patients with DTFSI and seven controls were included. Mean value and 95% CI for 3D Syndesmotic Incisura volumetric measurements at 10 and 15mm points: 1457 mm3 (1233 to 1680)/2241 mm3 (1951 to 2531) for controls, and 1679 mm3 (910 to 2447)/2425 mm3 (1408 to 3443) for patients with DTFSI (p-values of respectively 0.35 and 0.55).When comparing injured and uninjured DTFSI ankles, volume measurements at 10 and 15mm points were increased on injured ankles, with a Hodges-Lehmann difference of respectively 287 mm3 (p=0.19), and 186 mm3 (p=0.31). The partition model demonstrated that the volume of the first 10mm was the best predictor of DTFSI, with only 3% chances of DTFSI when the incisura volume was below 1291 mm3 (AUC=0.71). Conclusion: Our study aimed to describe and validate the use of a novel automatic 3D volumetric measurement of the distal tibiofibular incisura in patients with chronic subtle ankle syndesmotic instability and controls. Our preliminary results demonstrated increased volumes on injured ankles when compared to contralateral uninjured ankles and controls. Measurements performed within the first 10mm length of the syndesmosis were found to predict better the presence of syndesmotic instability, with a volume of 1291 mm3 representing an important diagnostic threshold. Automatic 3D WBCT volumetric measurements may represent a useful non-invasive diagnostic tool for subtle and chronic syndesmotic instability.

Category: Hindfoot Introduction/Purpose: An adult-acquired flatfoot deformity is a three-dimensional (3D) condition characterized by a loss of the medial longitudinal arch, valgus alignment of the hindfoot, and abduction of the midfoot. When conservative measures are not sufficient, a medializing calcaneal osteotomy (MCO) is frequently performed to correct the deformity, but there is lack of data on the associated three-dimensional variables defining the final correction. A possible reason for this shortcoming could be the current image-based analyses, mainly performed on bi-dimensional radiographs. These are hampered by errors in 3D rotations and superimposition of bony structures. The aim of this study was therefore to assess the correlation between the preoperative hindfoot valgus deformity and calcaneal osteotomy angle and the postoperative calcaneal displacement by use of weightbearing CT (WBCT). Methods: Weight-bearing CT scans obtained pre- and post-operatively were analyzed for sixteen patients with a mean age of 49.4 years (range: 18-66 years). Indication for surgery was adult-acquired flat foot deformity stage II. Based on the WBCT images, pre- and post-operative 3D bone morphological models of the tibia, talus, calcaneus, and the second metatarsal were created, on which anatomical bony landmarks were computationally identified to define a Foot Anatomical reference Frame (FAF). This FAF was used to measure valgus deformity pre- and post-operatively, inclination of the osteotomy plane, and displacement of the calcaneus (Fig. 1). Linear regression was conducted to assess the relationship between these measurements. Results: On average, the hindfoot valgus changed from 13.1° (±4.6) preoperatively to 5.7° (±4.3) postoperatively. A mean inferior displacement of 3.2 mm (±1.3) was observed along the osteotomy with a mean inclination angle of 54.6° (±5.6), 80.5° (±10.7), - 13.7° (±15.7) in the axial, sagittal and coronal planes, respectively. A statistically significant positive relationship (P < .05, R2 = 0.6) was found between the preoperative valgus, the axial osteotomy inclination, and the inferior displacement. Conclusion: This study shows that the degree of preoperative valgus of the hindfoot and the axial osteotomy angle are predictive factors for the amount of postoperative plantar displacement of the calcaneus. These findings contrast the general recommendation of performing a 90° calcaneal osteotomy angle, i.e. perpendicular to the lateral calcaneal wall in every patient. The obtained factors should be taken into account when performing a MCO and could be integrated in a computer-based pre- operative planning.

Category: Hindfoot Introduction/Purpose: Peritalar subluxation comprises part of the three-dimensional and complex distortion that occurs in patients with adult-acquired flatfoot deformity (AAFD) and is characterized by subluxation of the hindfoot through the triple joint complex. It is traditionally graded on weightbearing computed tomography (WBCT) coronal plane images, depending upon the degree of angulation and subluxation of the posterior facet of the subtalar joint. In this case-control study, we describe a new marker of peritalar subluxation represented by the amount of subluxation and joint incongruence of the middle facet of the subtalar joint. We hypothesized that the amount of joint subluxation and incongruence at the middle facet would be significantly increased in patients with AAFD when compared to controls. Methods: Case-control study, we included 30 patients with stage II AAFD (19 females/11 males), mean age 52.2 (range, 29 to 81) years, and 30 controls (18 females/12 males), mean age 49.3 (range, 28 to 83) years, that underwent WBCT as part of the evaluation of their foot condition. Age and gender were statistically similar in both groups. The amount of subluxation of the subtalar joint at the middle facet (% of uncoverage) and angle of joint incongruence, both measured at the midpoint of its longitudinal length, was measured in coronal WB CBCT images by two independent and blinded fellowship-trained foot and ankle surgeons. A second set of measurements was performed after one month (wash-out period). Intra- and interobserver reliability were assessed by Pearson/Spearman’s and Intraclass Correlation Coefficient (ICC), respectively. Comparison was performed using Paired Student T-Test or each pair Wilcoxon rank sum test. P-values lower than 0.05 were considered significant. Results: We found overall good to excellent intra- (range, 0.90-0.95) and interobserver reliability (range, 0.75-0.93) for the measurements. We found significantly increased subluxation of the subtalar joint at the middle facet in patients with AAFD, with a mean value for middle facet uncoverage of 45.3% (95% CI, 40.5% to 50.1%), when compared to 4.8% (95% CI, 0% to 9.6%) in controls (p

Category: Bunion Introduction/Purpose: Coronal plane rotational deformity of the first ray has been implicated with the developmental pathologic process of hallux valgus (HV). Weight Bearing CT (WBCT) is an imaging technology that can support the assessment of this complex three-dimensional (3D) deformity. The objective of the study was to analyze the 3D architecture of the first ray in patients with HV when compared to controls using WBCT images and a 3D biometric algorithm analyzing the deformity in all three planes. We hypothesized that WBCT would confirm the rotational deformity in HV patients, and that the 3D algorithm would demonstrate increased specificity and sensitivity for the pathology when compared to traditional two-dimensional (2D) HV measurements such as the 1-2 intermetatarsal angle. Methods: Retrospective case-control study, ethics committee approved. Twenty-one feet of patients with clinically symptomatic HV and 20 feet of asymptomatic controls were included. Exclusion criteria applied were previous trauma or surgery affecting first ray or forefoot morphology. All patients were assessed using WBCT. First ray 3D coordinates (x, y, z) were harvested including: center-points of the heads and bases of the first and second metatarsals, center-point of the medial and lateral sesamoids, distal condyles of the proximal phalanx (PP) of the first toe, as well as the medial and lateral borders of the first metatarsal head and diaphysis. The 2D measurements (dorsoplantar 1-2 intermetatarsal (IMA) and metatarsophalangeal (MPA) angles) were obtained using digitally reconstructed radiographs (DRR). The Sesamoid Rotation Angle (SRA) was measured in the coronal plane. Using these coordinates, all 2D, 3D axes, distances, angulations and 3D biometric for HV (HV-3DB) could be calculated. Results: Mean ages were respectively 62.2y in the HV group and 48.8y in the control group (p

Category: Ankle, Ankle Arthritis Introduction/Purpose: Peri-prosthetic cysts (PPC) in Total Ankle Replacement (TAR) are a common failure cause but the mechanisms of their development remains unclear. One possible explanation could be hindfoot malalignment and subsequent unequal distribution of load inside the joint. However, how residual malalignment influences the evolution of PPC remains unclear. Computed tomography (CT) has demonstrated superiority on conventional radiography in the follow up of PPC. Weight Bearing CT (WBCT), by combining 3D imaging and weight bearing measurements seems a valid tool to investigate this further. The objective for this work was to study the effects of residual hindfoot deformity on the distribution of PPC in the coronal plane. We hypothesized that cysts would be found predominantly medially in varus configuration, and laterally in valgus configuration. Methods: Retrospective comparative study, ethics committee approved. Forty-eight cases of TAR were included, with relevant demographics. Inclusion criteria were cases of primary TAR with available WBCT imaging of their ankle as part of normal follow up. Exclusion criteria were subsequent implant revision or cyst grafting. In each case, the localization and size of PPC’s were documented and their volume calculated by approximation of the closest ellipsoid. Hindfoot alignment was evaluated by the percentage Foot Ankle Offset (FAO) (foot-length normalized 3D ratio between the midline of the foot and the center of the ankle) using a WBCT dedicated semi-automatic software. The mean FAO value with 95%CI for the population was calculated. The difference in medial and lateral cyst volume defined by their position relative to the median axis in the coronal plane was compared in varus and valgus cases by a Mann-Whitney non-parametric test for unpaired samples. Results: Demographic distributions of the series were 32% female, mean age 65 (45-85) years. Mean FAO value was 0.12% (95%CI -1.09 to 1.33). Mean follow up was 43 months (6 to 239). The mean total cyst volume per case was 1190,7 mm3. In varus cases (defined by FAO1.33%), the volume of lateral cysts was greater than medially by a mean 332 mm3. The difference was statistically significant (p

Category: Radiolography Introduction/Purpose: Weight-bearing CT (WBCT) has been proven to allow for more precise and valid measurement of bone position than conventional weight-bearing radiographs (R) and conventional CT without weight-bearing (CT). Time spent for image acquisition has been shown to be lower for WBCT than for R and CT. Radiation dose for WBCT has been shown to be lower for WBCT than for CT. A WBCT device (PedCAT, Curvebeam, Warrington, PA, USA) had been brought on line July 1, 2013 in the first author´s foot and ankle department. The purpose of this study was to assess the benefit of using WBCT instead of R and/or CT in a foot and ankle center regarding time spent for image acquisition, radiation dose, disturbances, and cost effectiveness. Methods: All patients who obtained WBCT (PedCAT)from July 1, 2013 until September 30, 2018 were included in the study. Age, sex, primary pathology were analyzed. The time spent for image acquisition (T) was calculated based on an analysis of previous study as follows: R (bilateral feet dorsoplantar and lateral, metatarsal head skyline view), 902 seconds; CT (bilateral feet and ankle), 415 seconds; WBCT (bilateral), 207 seconds. Radiation dose (RD) per patient was calculated based on previous phantom measurements as follows: R, 1.4 uSv; CT, 25 uSv; WBCT 4.2 uSv1. For analysis cost effectiveness, device cost, reimbursement and working time cost of radiology technicians were taken into consideration within the local circumstances. All parameters were compared between the time period using WBCT (yearly average) with the parameters from 2012, i.e. before availability of WBCT. Results: 10,087 WBCT scans were obtained in 4,702 patients (4,702 (47%) before treatment; 5,385 (53%) follow-up; mean age, 52.0; 40% male). Primary pathologies were forefoot deformities (n=916 (20%) and ankle instability/cartilage defect (n=534 (13%)), and hindfoot deformity (n=480 (10%)). 1,940 WBCT scans were obtained on average yearly, and 10.4 CTs (WBCT group). In 2012, 1,850 R and 254 CTs were obtained (R(+CT) group). Yearly RD was 4.4 uSv for WBCT group and 4.8 uSv for R(+CT) group (difference 0.4 uSv decrease with WBCT 8%, p

Category: Midfoot/Forefoot Introduction/Purpose: Surgical planning based on angular measurements obtained on conventional radiographs is challenging due to perspective distortion and operator bias. Novel weightbearing CT (WBCT) three-dimensional (3D) measurements using coordinate systems may represent a more reliable and accurate evaluation of this 3D deformity. The objective of this study was to compare the M1-M2 intermetatarsal angle (IMA) obtained manually on WBCT digitally reconstructed 2D radiographs versus a set of coordinates from the full 3D dataset, in patients with hallux valgus (HV) deformity and in healthy controls. We hypothesised that the 3D measurements would be more reliably obtained, demonstrating different values when compared to 2D radiographic measurements. Methods: In this multicenter retrospective comparative study, 83 feet that underwent WBCT of the foot were included (41 HV: mean age 59, 81% female, 42 controls: mean age 52, 80% female). Datasets were analysed by three independent trained foot and ankle surgeons using the same protocol. Coordinates in three planes (x, y, z) of four different landmark points were harvested: center of the heads and midpoint of the proximal metaphysis of the 1st and 2nd metatarsal. The IMA measurements were then performed in reconstructed radiographic images (DRR-IMA). The data collected was then analyzed by a single 4th independent and blinded investigator who calculated the 3D angle (3D-IMA) and its projection on the weightbearing plane (2D-IMA). Intra-observer realiability was assessed by Pearson/Spearman’s correlation. Intermethod correlation was evaluated by intraclass correlation coefficient (ICC). Mean values for measures were comparared by One-way ANOVA. P-values of less than 0.05 were considered significant. Results: Intraobserver reliability was excellent for radiographic DRR-IMA (0.95) and 3D coordinates assessment (0.99). Intermethod correlation between the three different imaging modalities (DDR, 2D and 3D), considering bias and interactions, were respectively 0.71 and 0.51 in control and HV patients. IMA measurements were found to be similar when measured in DRR, 2D and 3D WBCT images, for both controls and HV patients. Mean values and confidence intervals (CI) for controls were 8.8 degrees (CI, 7.9-9.7) in DDR images, 9.8 degrees (CI, 8.7-10.9) in 2D images and 10.6 degrees (CI, 9.5-11.8) in 3D images. When compared to controls, HV patients demonstraded significantly increased IMA (p

Category: Sports Introduction/Purpose: Adequate evaluation of foot and ankle problems in elite athletes is paramount for planning the correct treatment, predicting clinical prognosis and supporting decision making. A complete physical examination that includes the assessment of foot alignment during weightbearing is mandatory. The three-dimensional evaluation provided by weightbearing CT imaging (WBCT) represent an important diagnostic tool for foot and ankle surgeons when dealing with these extremely physically active patients. The purpose of this study was to assess different WBCT measurements of hindfoot and forefoot alignment in injured high-level football and basketball players. We hypothesized that specific patterns of hindfoot alignment and height of the longitudinal arch of the foot could be identified. Methods: In this single center retrospective comparative study, 80 professional male athletes - 47 basketball and 33 American football players from College, NBA and NFL leagues - that underwent WBCT as part of the clinical investigation for different injuries of the foot and ankle were included in the study. WBCTs images were evaluated by a blinded board-certified foot and ankle orthopedic surgeon. Multiple measurements used for assessment of hindfoot valgus and longitudinal arch height were assessed and included: foot and ankle offset (%), calcaneal offset (mm), hindfoot alignment angle (°), navicular-floor distance (mm), medial cuneiform-floor distance (mm), forefoot arch angle (°), inferior talar-superior talar angle (°), and subtalar horizontal angle (°). An unpaired Student’s t test was performed to evaluate any differences in the measurements when comparing professional basketball and football patients. P-values less than 0.05 were considered significant. Results: A summary of demographic characteristics and each measurement’s distributions and standard deviations, as well as p-values for the analysis between groups, is given in table 1. No significant differences were found between basketball and American football elite athletes when comparing the mean values of measurements evaluated (mean differences): foot and ankle offset (0.26%), calcaneal offset (0.58 mm), hindfoot alignment angle (0.73°), navicular-floor (0.35 mm) and medical cuneiform-floor distances (0.38 mm), forefoot arch angle (0.74°), inferior talar–superior talar angle (0.83°) and subtalar horizontal angle (0.1°). Conclusion: Although we did not find significant differences in foot alignment when comparing basketball and American football professional athletes, the results of our study highlight some of the important foot alignment parameters and establish distributions in an extreme but important population. Further studies correlating foot alignment with the incidence of some of the most common pathologies diagnosed in elite athletes, such as the ones reported in our study, can help in the understanding and prevention of those injuries.

Category: Hindfoot Introduction/Purpose: Hindfoot alignment is an important reference for foot and ankle surgery, and the Foot Ankle Offset (FAO) using semi-automatic software has been reported as a valuable hindfoot alignment measurement in weightbearing CT(WBCT). The objective was to assess the clinical relevance and reproducibility of the FAO value for hindfoot alignment and compare it with previous findings. Methods: A prospective study was conducted, with ethics committee approval. Patients were included, clinically examined and divided into 3 groups: normal alignment (Group 1), valgus (Group 2), varus (Group 3). A continuous series of 140 feet (71 patients) were referred from September to December 2017 (65 normal, 41 valgus, and 34 varus). All patients had a bilateral weight bearing CT, and the FAO values were recorded. The long axial view angle(HAct)was measured on Digitally Reconstructed Radiographs (DRR) as comparison. All values were measured and compared by two different investigators. The reproducibility of FAO and HAct were calculated using intraclass correlation coefficients(ICCs) and regression analysis was conducted to study the correlation between the two methods. Results: In Group 1, the mean value for FAO/HAct was 1.69%±2.58%/4.13±2.67, in Group 2, the FAO/HAct was 7.46%±3.18%/9.00±3.43; in Group 3 the values were -6.11%±4.55%/-7.49±6.06. The intra- and interobserver reliability were 0.991/0.992 and 0.976/0.976. There was a good linear correlation between HAct and FAO (R2=0.778, and the regression slope was 1.083. Conclusion: The use of weightbearing CT can help characterize hindfoot alignment objectively using WBCT. The present study is the first prospective comparative assessment of this technology and shows that FAO has good repeatability, and it correlates well with clinical examination,, X ray findings and previous literature. The FAO is a clinically relevant and reproducible method for measuring hindfoot alignment.