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Category: Basic Sciences/Biologics; Basic Sciences/Biologics Introduction/Purpose: Screws generate and maintain compression against distracting forces when performing osteotomy or fusion surgery. Headless screws with opposing flank angles (OFA) between the threads of the head and shaft are purported to achieve better compression. The purpose of this study was to compare OFA designs against traditional parallel flank angle (PFA) headless screws and headed screws to determine differences in compression and pull-out resistance (POR). Methods: In this biomechanical in-vitro study, four screw designs were compared: headless screws with OFA (Screw_A and Screw_B), headless screws with PFA (Screw_C), and headed screws (Screw_D). All screws were 4.0x50mm partially threaded cannulated screws. Screw_B had a 1.4mm shorter head length and 0.5mm narrower head thread diameter than Screw_A and Screw_C, which were similar. A custom apparatus was designed for measuring compression and POR. Osteotomies were created on synthetic bone blocks (density 0.32g/cm3) simulating cancellous bone. Screws were inserted perpendicular to osteotomies in accordance with manufacturer guidance and maximum compression recorded. Increasing distracting forces were then applied to the blocks until the screws pulled out. For each screw type, five screws were tested. Results: There was no significant difference in maximum compression between screw designs: Screw_A=38.7N±14.2N, Screw_B=48.7N±15.6N, Screw_C=51.9N±36.4N, Screw_D=32.0N±9.2N; p=0.921. When assessing POR, all screws failed at the head-bone interface (screw heads subsided into block). Pull-out forces significantly differed between all groups: Screw_A=466N±29.0N, Screw_B=310N±22.0N, Screw_C=399N±46.0N, Screw_D=183N±12.9N; p< 0.001 (ANOVA). Screw_Ahad the highest POR but the other OFA design (Screw_B) had significantly lower POR. Conclusion: Screw design, whether headless (OFA or PFA) or headed did not appear to influence compression generated. However, headed screws had significantly lower POR than headless designs. Within headless designs, OFA may increase POR, but other screw head features (number / diameter of threads) had an apparently greater influence than flank angle.

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: 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: 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: 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: Sports; Hindfoot Introduction/Purpose: Plantar fasciopathy (PF) is a common orthopaedic condition which often affects athletes and limits their performance. Our aim was to conduct a scoping review of the literature in order to summarise the evidence provided so far in the management of PF in Elite Athletes and identify potential gaps in the current knowledge. Methods: This scoping review followed the six-stage methodological framework of Arksey and O'Malley and was registered in the Open Science Framework (10.17605/OSF.IO/48S3K). Pubmed, Scopus and Web of Science were used to identify elegible papers. After charting of data, studies were pooled into three categories: 1) epidemiological/diagnostic studies, 2) outcome research and 3) studies on the rupture of the plantar fascia. The modified Coleman Methodology Score (mMCS) was used to assess the quality of manuscripts included. Results: Out of 742 initial studies, 10 were selected (109 patients) including 8 Level IV and 2 Level V articles. In four studies (91 athletes), potential risk factors (i.e. pre-existent thickening of the fascia, spike shoes, varus hindfoot/knee alignment) were discussed. In three studies (6 athletes), focusing on plantar fasciitis, the non-surgical treatment led to a satisfactory but poorly- documented outcome. In three studies (12 athletes), the rupture of the fascia was treated conservatively with contrasting results, while surgery was performed only in 2 cases. The mean mCMS was 19 (range, 3 to 42), demonstrating overall poor methodology. Conclusion: The limited number of studies and their poor quality do not allow to define the gold standard treatment of PF in Elite Athletes. Until high-quality studies are provided, clinicians have to rely on the available literature regarding the non- professional or non-athletic population to make the best evidence-based decision.

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: 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; 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: 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; 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: Hindfoot; Midfoot/Forefoot 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 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.