Background: Varus hindfoot deformity may increase the risk of chronic lateral ankle instability (CLAI). Our aim was to analyze hindfoot alignment (HFA) in patients with CLAI using weight-bearing cone beam computed tomography (WBCT) to assess this risk. Methods: This retrospective, comparative analysis was carried out using an existing WBCT database (Talas, CurveBeam LLC), including data sets for 370 consecutive feet (189 patients) obtained between July 2016 and October 2018 at a single institution. The software provided semiautomated measurement of HFA, given as foot ankle offset (FAO). Univariate analysis was conducted to compare feet with and without CLAI against sex, age, body mass index, and FAO. Significant variables were included in a multivariable logistic model with random effects to take into account correlation between feet of the same patient. Results: Forty-three feet had CLAI (34 patients). FAO ( P = .0009) was significant for CLAI by univariate analysis. Mean FAO was −2.2% ± 5.5% (varus) and + 2.6% ± 4.7% (valgus) with and without CLAI history, respectively. Multivariable logistic regression adjusted for sex and age demonstrated a 35% increased odds ratio (OR) of CLAI per 1% reduction in FAO value (varus) (adjusted OR=0.64, 95% confidence interval [CI]: 0.49-0.84; P = .001) and no significant effect of sex (adjusted OR=0.52; P = .617) or age (adjusted OR=0.94; P = .165) after adjustment for FAO. Conclusion: A positive relationship was found between varus HFA and the risk to have CLAI. Systematic recording of FAO measurements from WBCT images along with clinical data regarding CLAI history proved successful at quantifying the risk of CLAI. Level of Evidence: Level III, retrospective cohort study.

Background: We investigated the association between hindfoot residual malalignment assessed on weightbearing computed tomography (WBCT) images and the development of periprosthetic cysts (PPCs) after total ankle replacement (TAR). We hypothesized that PPCs would be found predominantly medially in the varus configuration and laterally in the valgus configuration. Methods: Cases of primary TAR with available WBCT imaging of the ankle were included in this retrospective study. The location of the PPC was marked and the following volumes were calculated: total (TCV), medial (MCV), central (CCV), and lateral (LCV) cyst volumes. Hindfoot alignment was measured as Foot and Ankle Offset (FAO), with 95% confidence intervals (95% CIs) calculated to define varus (<95% CI) and valgus (>95% CI) groups. Cyst volumes were compared between these 2 groups. The American Orthopaedic Foot & Ankle Society (AOFAS) score at the time of the WBCT was also retrieved. Receiver operating characteristic (ROC) curves were used to determine FAO thresholds for predicting an increased risk of PPC. Results: Forty-eight TARs (mean follow-up, 44.6 months) were included, 81% of which had at least 1 PPC. The mean FAO was 0.12% (95% CI, –1.12 to 1.36). Patients with greater residual malalignment ( P < .001) and those with longer follow-up ( P < .001) presented with increased TCV. In varus cases, the MCV was greater than the LCV ( P = .042), with a threshold FAO value of −2.75% or less predicting an increased MCV. In valgus cases, the LCV was greater than the MCV ( P = .049), with a FAO threshold value of 4.5% or more predicting an increased LCV. Conclusion: In this series, the PPC volume after primary TAR significantly correlated with postoperative hindfoot malalignment and longer follow-up. Level of Evidence: Level III, retrospective comparative series.

Background: Weightbearing cone beam computed tomography (WBCT) has been gaining traction as a useful imaging modality in the diagnosis and follow-up of foot and ankle musculoskeletal pathologies due to the ability to perform quick, low-dose, 3-dimensional (3D) scans. However, the resulting wealth of 3D data renders daily clinical use time-consuming. The aim of this study was to evaluate a new artificial intelligence (AI)–based automatic measurement for the M1-M2 intermetatarsal angle (IMA) in hallux valgus (HV). We hypothesized that automatic and manual measurements would have a strong correlation, and that the AI software would yield better reproducibility and would be faster compared with manual measurements. Methods: This was a multicenter retrospective comparative case-control study in which a total of 128 feet were included from 93 patients who underwent WBCT scans as part of their routine follow-up: 59 feet with symptomatic HV and 69 controls. The IMA was measured automatically using the AI software and manually on digitally reconstructed radiographs (DRRs). The AI software produced both an automatic 2D (auto 2D) and 3D (auto 3D) measurement. Results: There were strong intermethod correlations between the DRR IMA and the auto 2D (HV, r = 0.61; control, r = 0.60; all P < .0001) and auto 3D (HV, r = 0.63; control, r = 0.52; all P < .0001) measurements, respectively. The intrasoftware reproducibility was very close to 100%. Measurements took 23.6 ± 2.31 seconds and 14.5 ± 1.18 seconds, respectively, when taken manually on DRRs and automatically. Controls demonstrated a mean DRR IMA of 8.6 (95% CI, 8.1-9.1), mean auto 2D of 11.2 (95% CI, 10.7-11.7), and mean auto 3D IMA of 11.0 (95% CI, 10.5-11.5). The HV group demonstrated significantly increased IMA compared with controls ( P < .0001), with a mean DRR IMA of 15.4 (95% CI, 14.8-16.1), mean auto 2D of 17.8 (95% CI, 17.2-18.4), and mean auto 3D IMA of 16.8 (95% CI, 16.8-17.4). Conclusion: Measurements generated by the WBCT AI-based automatic measurement system for IMA demonstrated strong correlations with manual measurements, with near-perfect reproducibility. Further developments are warranted in order to make this tool more usable in daily practice, particularly with respect to its use in the presence of hardware in the foot. Level of Evidence: Level III, retrospective comparative study.

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Background: Weightbearing computed tomography (WBCT) 3-dimensional measurements may be reliable in assessing hallux valgus (HV). The objective of this study was to compare 2D and 3D WBCT measurements of the M1-M2 intermetatarsal angle (IMA) in patients with HV and in healthy controls. We hypothesized that 2D and 3D IMA measurements would correlate and have similar reliability in both HV and controls. Methods: Retrospective multicenter comparative study included WBCT scans from 83 feet (41 HV, 42 controls). IMA was measured on digitally reconstructed radiographs (DRR-IMA). 3D angle (3D-IMA) and its projection on the weightbearing plane (2D-IMA) were calculated from 3D coordinates of the first and second metatarsals. Intraobserver reliability and intermethod correlations were calculated using intraclass correlation coefficients (ICCs). Results: Intraobserver reliability was very strong for DRR-IMA (0.95) and 3D-IMA (0.99). Intermethod correlation between the 3 modalities in HV patients ranged from moderate (DRR vs 2D, 0.48; DRR vs 3D, 0.48) to very strong (2D vs 3D, 0.91). Similarly, intermethod correlation in the control group ranged from moderate (DRR vs 2D, 0.56; DRR vs 3D, 0.60) to very strong (2D vs 3D, 0.92). Conclusion: Measurements for IMA are similar using DRR, 3D and 2D projected angles, with very strong intraobserver reliability and moderate to very strong intermethod correlations. This is the first head-to-head comparison between these measurement modalities in HV. Further investigations are warranted before formulating guidelines for the clinical use of 3D angles. Level of Evidence: Level III, case-control study.

Category: Ankle; Basic Sciences/Biologics; Hindfoot Introduction/Purpose: Abnormal Hindfoot Alignment (HA) has been correlated with increased failure rates in ankle fusion or replacement for osteoarthritis (OA). An altered stress distribution in the surrounding bone and abnormal Bone Mineral Density (BMD) around the native ankle may be predisposing factors for those unwanted outcomes. Cone Beam Weight Bearing CT (WBCT) has recently been used to investigate BMD and to correlate the localization of periprosthetic cysts and alignment in ankle arthroplasty. The objective of this study was to assess the spatial distribution of BMD around the ankle joint in patients with normal or abnormal HA. We hypothesized that BMD would be evenly distributed in normally-aligned ankles whilst increased medially in varus and laterally in valgus configurations. Methods: In this retrospective comparative Level III study, 60 ankles (41 adults),without any trauma or surgery affecting HA, with WBCT datasets (PedCat, Curvebeam LLC, PA-USA) were allocated to 3 groups (comparable by age, p=0.79; BMI, p=0.24; and side, p=0.93), based on the Foot Ankle Offset (FAO) values: 20 normal (0%-2), 20 varus (FAO< 0%; 35% female, age 48.8+-13 years, BMI 26.2+-2.9 kg.m-2), and 20 valgus (FAO>5%; 40% female, age 58.9+-14.6 years, BMI 28.6+-4.2 kg.m-2). Semi-Automatic Segmentation (BoneLogic, Disior Oy, Helsinki-Finland) was applied to identify bones of interest. The 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. The primary outcome measure was the Medial over Lateral HU ratio (M/L-HU). Comparisons were performed using one-way ANOVA, Kruskal-Wallis and Chi2 tests. Results: All values of BMD were normally distributed but M/L-HU ratios were not. Mean +- standard deviation HU values in the compartments in normal cases were 523+-103 (medial tibia), 519+-115 (lateral tibia) 421+-81 (medial talus), 470+-92 (lateral talus) and 725+-109 (fibula). The mean BMD was significantly lower in all compartments in valgus cases compared to normal (all p<0.05). It was decreased in valgus vs varus in the talus (p<0.04), specifically in the medial compartment (p<0.01). The tibia M/L- HU ratio was decreased in valgus vs normal (0.87+-0.16 vs 1.01+-0.07; p=0.001) and vs varus (1.04+-0.09; p<0.001). The talus M/L-HU ratio was increased in varus cases vs normal (1+-0.22 vs 0.83+-0.09; p<0.01) and valgus (0.07+-0.19; p<0.001). Conclusion: We found that BMD in distal tibia, fibula and the talus varies with hindfoot alignment. In valgus configuration, all bone compartments were less dense compared to normal and varus. The medio-lateral ratio increased in the tibia and in the talus in varus cases, suggesting medial concentration of bone, and decreased in valgus cases, suggesting a more lateral concentration. This data supports the role of WBCT in analyzing BMD distribution. This method could be clinically useful in ankle OA to evaluate bone quality for such considerations as surgical indications or implant positioning.

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Category: Ankle, Ankle Arthritis Introduction/Purpose: Peri-prosthetic cysts (PPC) in Total Ankle Replacement (TAR) are a common failure cause but the mechanisms of their development remains unclear. One possible explanation could be hindfoot malalignment and subsequent unequal distribution of load inside the joint. However, how residual malalignment influences the evolution of PPC remains unclear. Computed tomography (CT) has demonstrated superiority on conventional radiography in the follow up of PPC. Weight Bearing CT (WBCT), by combining 3D imaging and weight bearing measurements seems a valid tool to investigate this further. The objective for this work was to study the effects of residual hindfoot deformity on the distribution of PPC in the coronal plane. We hypothesized that cysts would be found predominantly medially in varus configuration, and laterally in valgus configuration. Methods: Retrospective comparative study, ethics committee approved. Forty-eight cases of TAR were included, with relevant demographics. Inclusion criteria were cases of primary TAR with available WBCT imaging of their ankle as part of normal follow up. Exclusion criteria were subsequent implant revision or cyst grafting. In each case, the localization and size of PPC’s were documented and their volume calculated by approximation of the closest ellipsoid. Hindfoot alignment was evaluated by the percentage Foot Ankle Offset (FAO) (foot-length normalized 3D ratio between the midline of the foot and the center of the ankle) using a WBCT dedicated semi-automatic software. The mean FAO value with 95%CI for the population was calculated. The difference in medial and lateral cyst volume defined by their position relative to the median axis in the coronal plane was compared in varus and valgus cases by a Mann-Whitney non-parametric test for unpaired samples. Results: Demographic distributions of the series were 32% female, mean age 65 (45-85) years. Mean FAO value was 0.12% (95%CI -1.09 to 1.33). Mean follow up was 43 months (6 to 239). The mean total cyst volume per case was 1190,7 mm3. In varus cases (defined by FAO<-1.09%), the volume of medial cysts was greater than laterally by a mean 197 mm3, whereas in valgus cases (defined by FAO>1.33%), the volume of lateral cysts was greater than medially by a mean 332 mm3. The difference was statistically significant (p<0.05). There was a weak, significant positive correlation (r=0.25, p<0,001) between FAO and total cyst volume and a moderate, significant correlation (r=0,56, p<0,001) between time to follow up and total cyst volume. Conclusion: Our hypothesis was confirmed. Periprosthetic cysts volume in this series of primary TAR was found to be relatively greater medially in postoperative varus configurations and vice-versa laterally in valgus. This confirms a possible correlation between the direction of residual hindfoot malalignment and the coronal localization of PPC in TAR, although this is certainly not the only pathophysiologic factor involved in PPC onset. Weightbearing CT may be helpful in Total Ankle Replacement follow up, in order to early detect PPC development and possibly to identify situations at risk of a more rapid evolution.