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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

The decade from 2010–2020 has seen the development of cone beam weight-bearing CT (WBCT) as a major innovation in the foot and ankle realm, becoming an important modality for bone and joint imaging. The ability to provide three-dimensional images of the naturally loaded skeleton has enabled several subsequent innovations to arise with aims to hasten image processing and to extend the clinical applications of WBCT. The objective of this work was to identify, categorize and explain those emerging techniques. We performed a structured review of the literature according to PRISMA standards, finally including 50 studies. We subsequently proposed a classification of these techniques. Segmentation and distance mapping were identified as key features. We conclude that although WBCT has already been adopted in a number of clinical communities with an immediate improvement in patient workflows, adoption of advanced techniques is yet to come. However, that relies mostly not on the technology itself, but on improvements in AI software allowing practitioners to quickly process images in daily practice and enabling the clinicians to obtain an accurate three-dimensional evaluation of the segment considered. Standardization will be paramount to amass large amounts of comparable data, which will fuel further innovations in a potentially virtuous circle.

Category: Basic Sciences/Biologics; Hindfoot Introduction/Purpose: It has become a reality with the advent of weight bearing CT (WBCT) that weight bearing (WB) is a significant element to be considered when analyzing foot and ankle images. Some knowledge has begun to accumulate on the effect of WB on bone positioning, but the effect of WB on bone mineral density (BMD) distribution, apart from being a long for accepted truth since the works of Julius Wolff, could not until now be visualized other than on the biological level. Now, Hounsfield Units allow for bone density analysis on WBCT. The objective of the study was to compare the relative positions of the geometric foot center (GC) and the density-weighted foot center (DC). We hypothesized those to be different. Methods: Ethics approval was obtained. Thrity two feet from our WBCT database were retrospectively randomly selected (Curvebeam Pedcat, Hatfield PA, USA). Datasets were analyzed using Bonelogics software (Disior, Paragon 28, USA). Bone segmentation was performed to obtain all bone orientations and volumes excluding tibia and fibula and all phalanges. The data was computed to obtain the geometric centers (from bone surface coordinates), which were considered as reference and were given a value of 0. Therefore density-weighted centers (from all bone data including density) were calculated. The difference between the two centers represented the shift which was assessed along the sagittal axis (anterior shift), transversal axis (lateral shift) and craniocaudal axis (upward shift). Statistical analysis was conducted using STATA package. Results: The mean age and Body Mass Index of the cohort were 57.2 ± 9.6 years and 22.2 ± 2.8 kg/m 2 , respectively. The 3D displacement vector between GC and DC had a norm of 10.01 mm. We found that DC was significantly shifted anteriorly by 8.9 ± 0.3 mm (range, 5.6 mm to 13.4 mm), medially by 0.4 ± 0.8 mm (range, -1.3 mm to 0.3 mm) and upwardly by 4.2 ± 0.14 mm (range, 2.8 mm to 5.9 mm) (p < 0.001 in all cases). Conclusion: Our hypothesis was confirmed: the geometric and weighed foot centers were different. DC was more anteriorly and slightly medially situated. Both centers were situated at the interface between the talus and cuboid. The more anterior position may be explained by the fact that human foot is responsible for anteriorly orientated longitudinal movement on average. We deem that BMD is a significant dimension in WBCT datasets that cannot be ignored in the development of new measurement tools that are not currently standardized. Alignment based purely on bone outer shape without considering BMD may not be representative of their true biomechanical state.

Category: Hindfoot; Arthroscopy Introduction/Purpose: Supramalleolar osteotomies have been proposed as surgical option to realign the ankle joint in case of altered intra-articular loading. Little is known about the changes occurring at the tibiotalar joint after inframalleolar procedures, such as the corrective arthroscopic anterolateral subtalar arthrodesis (ALAPSTA). We set out to investigate changes in terms of joint interaction between the articular surfaces at the tibiotalar joint after corrective anterolateral arthroscopic subtalar arthrodesis (ALAPSTA) to treat Progressive Collapsing Foot Deformity (PCFD) with sinus tarsi impingement and subtalar joint degeneration. We hypothesized that ALAPSTA would improve hindfoot malalignment and that the distances between articular surfaces at the ankle would change significantly. Methods: In this retrospective study, we evaluated a consecutive series of 33 feet from 33 patients (mean age 60 years, SD 16.2; 16 right and 17 left) diagnosed with PCFD undergone ALAPSTA and reassessed at a mean follow-up of 7 months (range, 2 to 50). Weightbearing computed-tomography (WBCT) images were retrieved and the Foot and Ankle Offset (FAO) was calculated to assess the hindfoot alignment. Distance Mapping (DM) at the ankle joint (divided in 9 regions) allowed to assess changes in terms of joint interaction at this level between pre and postoperative images. Results: Hindfoot alignment significantly improved with a pre-operative FAO at 10.7 points (SD 4.7) and a post-operative FAO at 4.8 (SD 4.9) (p < 0.001). The mean improvement was 5.6 points. We found a significant increase in mean distances occurring posterolaterally at the ankle (from 4.5 mm (SD 1.2) to 5.4 mm (SD 1.5), p< 0.001) along with a significant decrease occurring anteromedially (from 9.1 mm (SD 1.2) to 8.3 mm (SD 1.4), p< 0.001). Conclusion: In this series, ALAPSTA was effective at correcting hindfoot malalignment in PCFD. After the procedure, the interaction at the ankle joint significantly changed with a reduction of anteromedial distance and an increase of posterolateral distance. Inframalleolar procedures seem to alter significantly the interaction between the tibia and the talus at the ankle. Further studies are warranted to ascertain whether changes in distances between surfaces correspond to changes in intra-articular pressures.

Category: Basic Sciences/Biologics; Hindfoot Introduction/Purpose: Weight-bearing CT (WBCT) enables accurate 3D hindfoot alignment (HA) measurements such as the Foot Ankle Offset (FAO). However, this uses anatomical landmarks and oversimplifies anatomy. Stress distribution influences bone mineral density (BMD). Hounsfield units (HU) are the tomographic measurement unit for BMD. We aim to analyze the distribution of BMD in the foot bones, relative to the long axis of the second metatarsal (M2), an accepted landmark for foot orientation, and its correlation with HA. Methods: In this retrospective study, 81 feet (27 per HA group : normal, valgus or varus) were included from our database after ethics approval. After 3D segmentation, a HU-weighted map (HUM) of the foot was projected on the ground plane with orientation defined by the longitudinal axis of the 2nd metatarsal. A HU Curve (HUC) was drawn, corresponding to the center of mass of the HUM in the coronal plane. We studied the HU angle (HUA) formed by HU Line (HUL) (linear regression of the HUC) and M2 longitudinal axis. Results: The groups were comparable by age, sex and BMI. A positive correlation between FAO and HU angle was found (r =0.75, p< 0.001). HUA were -0.4° ± 5.5° in varus, 3.5° ± 6.8° in normals, 13.4° ± 5.1° in valgus (F=39.7 and p< 0.001). HUA differences were significant between normals and varus (p < 0.05), and between normals and valgus (p < 0.001). FAO and HUA were significantly correlated in valgus (rho=0.437, p=0.002) and varus (rho=0.540, p=0.004). Conclusion: We found altered distributions in misaligned cases, and BMD was correlated with HA. The HUL could be an interesting new tool to analyse the topography of bone distribution in WBCT.

Category: Bunion; Midfoot/Forefoot Introduction/Purpose: The outcomes of Hallux Valgus (HV) surgical treatment are perfectible. First ray dysmorphia in HV appears to incorporate a first metatarsal (M1) hyperpronation and a valgus deviation of M1 distal articular surface. Those could play a role in first ray destabilization and misalignment in HV. However, we do not know whether correction of these deformities could improve HV surgical treatment outcomes. Therefore, we performed a study to assess the impact of M1 distal supination osteotomy, M1 distal varization osteotomy, and combination of both on HV clinical and radiological outcomes. We hypothesized that M1 distal supination osteotomies would improve surgical outcomes in HV. Methods: We conducted an IRB-approved multicenter randomized control trial. HV with an indication for surgical correction were included. HV requiring surgery of the lesser metatarsals were excluded. Feet were randomly divided into 4 groups corresponding to 4 different types of surgery (Figure): 1. Control, classical M1 distal chevron. 2. Supination M1 distal chevron 3. Varization M1 distal chevron 4. Combination of the latter two. Preoperative evaluation and 6-months follow-up were performed. Demographics, AOFAS score, complications, and patient satisfaction (Likert Scale) were collected. On conventional weight-bearing radiographs before and 6 months after surgery, we measured the Hallux Valgus Angle(HVA), the Intemetatarsal Angle(IMA) the Distal Metatarsal Articular Angle(DMAA), the Okuda's M1 head shape classification(from round to angular) and the sesamoid position according to Hardy and Clapham. Normality of different variables was assessed using the Shapiro-Wilk test. Groups were compared using ANOVA for normal and Kruskall Wallis for nonnormal variables. Post-hoc pairwise analyses were performed with Dunn-Bonferoni’s test. Results: 100 HV were included. 8 were lost to follow-up. The Control (n=24), Supination (n=20), Varization (n=26) and Combination (n=22) groups were comparable on age, gender, BMI, and preoperative radiological parameters. At 6 months, there was no difference on AOFAS improvement (p=0.39) and patients satisfaction (p=0.14) whereas there were significant differences on HVA (p < 0.001), IMA (p < 0.001), DMAA (p < 0.001), Okuda's classifcation (p < 0.001) and sesamoid position (p < 0.001) between groups. We found lower HVA values for Combination VS Control (p < 0.001), Combination VS Varization (p < 0.001), Supination VS Control (p < 0.001) and Supination VS Varization (p = 0.005). Asymptomatic recurrences (HVA>15°) were present in 5 cases in Control (20.8%), and 2 in Varization (7.7%). Asymptomatic Hallux Varus (HVA < 0°) were present in 4 cases in Combination (18.2%), and 1 in Supination (5%). Conclusion: Distal M1 supination osteotomies showed better improvement in radiological parameters without showing clinical benefit. The combination of supination and varization osteotomies could lead to overcorrection while the classic M1 distal chevron could lead to insufficient corrections. Routinely performing a supination osteotomy in HV surgical management may lead to erroneous correction and we recommend an à la carte treatment. These results are preliminary and we recommend more patients and longer follow-up to confirm these findings.

Category: Midfoot/Forefoot; Hindfoot Introduction/Purpose: The current classification system of progressive collapsing foot deformity (PCFD) is comprised of 5 possible classes. 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: We retrospectively assessed weight-bearing computed tomography (WBCT) measurements of 32 feet with PCFD diagnosis. 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 Meary’s 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. A p-value < 0.05 was considered significant. Results: Class A showed a substantial positive correlation with class C (ρ=0.71; R2=0.576; p 0.001). Class B was substantially correlated with class D (ρ=0.74; R2=0.613; p 0.001). Class C showed a substantial positive correlation with class A (ρ=0.71; R2=0.576; p 0.001) and class D (ρ=0.75; R2=0.559; p 0.001). Class D showed a substantial positive correlation with class B and class C (ρ=0.74; R2=0.613; p 0.001), (ρ=0.75; R2=0.559; p 0.001) respectively. Class E did not show correlation with class B, C, or D (ρ=0.24; R2=0.074; p=0.059), (ρ=0.17; R2=0.071; p=0.179), and (ρ=0.22; R2=0.022; p=0.082) respectively. The average values of each class radiographic markers are listed in Figure 1. Conclusion: This study was able to find relations between components of PCFD deformity with exception of ankle valgus deformity (Class E). Measurements associated with each class were influenced by others, and in some instances, with pronounced strength such as between class A and C as well as between Class B and D. Surgical procedures to address certain class deformities could indirectly address other classes as well, which ultimately decreases surgical procedures numbers or complexity. The presented data may support the notion that PCFD is a three-dimensional complex deformity and suggests a possible relation among its ostensibly independent features.

Abstract The early effects of progressive collapsing foot deformity (PCFD) on the ankle and syndesmotic joints have not been three-dimensionally quantified. This case-control study focused on using weight bearing CT (WBCT) distance (DM) and coverage maps (CM) and volumetric measurements as 3D radiological markers to objectively characterize early effects of PCFD on the ankle and syndesmotic joints. Seventeen consecutive patients with symptomatic stage I flexible PCFD and 20 matched controls that underwent foot/ankle WBCT were included. Three-dimensional DM and CM of the ankle and syndesmotic joints, as well volumetric assessment of the distal tibiofibular syndesmosis was performed as possible WBCT markers of early PCFD. Measurements were compared between PCFD and controls. Significant overall reductions in syndesmotic incisura distances were observed in PCFD patients when compared to controls, with no difference in the overall syndesmotic incisura volume at 1, 3, 5 and 10 cm proximally to the ankle joint. CMs showed significantly decreased articular coverage of the anterior regions of the tibiotalar joint as well as medial/lateral ankle joint gutters in PCFD patients. This study showed syndesmotic narrowing and decreased articular coverage of the anterior aspect of the ankle gutters and talar dome in stage I PCFD patients when compared to controls. These findings are consistent with early plantarflexion of the talus within the ankle Mortise, and absence of true syndesmotic overload in early PCFD, and support DM and CM as early 3D PCFD radiological markers.