Statistical Shape Modeling Enables Identification of Subtalar Contact Stress Differences Following Tibiotalar Arthrodesis and Total Ankle Replacement

Category: Hindfoot; Ankle Arthritis Introduction/Purpose: Clinical studies have shown 32% of patients with a TAR progress to subtalar OA within 5 years, whereas 78% of patients with a tibiotalar arthrodesis presented with subtalar OA by 7.5 years. Higher rates of subtalar OA after arthrodesis may be explained by a transfer of ankle forces and stress through the adjacent subtalar joint while TAR may mitigate these changes. The objective of this study was to compare subtalar joint contact stresses between patients treated with tibiotalar arthrodesis and total ankle replacement (TAR) during an overground walking activity using correspondence particles to enable regional analysis. Methods: With IRB approval, ten individuals with unilateral tibiotalar arthrodesis and six individuals with unilateral TAR were imaged with biplane fluoroscopy during overground walking. Discrete element analysis (DEA) was performed to estimate subtalar joint contact stress using the tracked bone models. Cartilage was modeled using linear-elastic material properties (E=12 MPa, v=0.42) and uniformly extruded compressible surfaces from rigid subchondral bone (0.98 mm talar side, 0.75 mm calcaneal side1). A calcaneal statistical shape model (SSM) was created and resulting correspondence particles served as registered locations for comparison of cumulative stress across three phases of normalized stance (loading-response 0-24%, mid 25-54%, and terminal 55- 87%). Two-sample t-tests or Wilcoxon rank-sum tests were used to evaluate differences (p < 0.05) in cumulative contact stresses at each correspondence particle within the 3 phases based upon Shapiro-Wilk findings of normality. Results: There were significant differences in contact stress exposure across all three phases of gait. Differences were identified along the superior-medial aspect of the posterior facet and within the anterior facet (Figure 1). Higher cumulative stresses were observed along the border of the posterior facet and in the medial facet. This model is limited by a lack of validation, uniform cartilage thickness assumptions applied across groups, and that DEA only estimates contact stress without consideration of shear. Conclusion: This study was the first to localize regional differences in subtalar joint stress for patients having undergone TAR and tibiotalar arthrodesis. Interestingly, TAR patients experienced higher stress in this study compared to those with arthrodeses. These ostensibly counterintuitive findings of higher TAR stress may relate to the pre-existence of subtalar OA which is a common indication of TAR versus fusion

Diagnostic accuracy of measurements in progressive collapsing foot deformity using weight bearing computed tomography: A matched case-control study

We aimed to investigate the diagnostic accuracy of known two-dimensional (2D) and three-dimensional (3D) measurements for Progressive Collapsing Foot Deformity (PCFD) in weight-bearing computed tomography (WBCT). We hypothesized that 3D biometrics would have better specificity and sensitivity for PCFD diagnosis than 2D measurements

Objective Metric of Energy Absorbed in Tibial Plateau Fractures Corresponds Well to Clinician Assessment of Fracture Severity

ObjectivesDetermine the agreement between subjective assessments of fracture severity and an objective computed tomography (CT)-based metric of fracture energy in tibial plateau fractures.MethodsSix fellowship-trained orthopaedic trauma surgeons independently rank-ordered 20 tibial plateau fractures in terms of severity based on anteroposterior and lateral knee radiographs. A CT-based image analysis methodology was used to quantify the fracture energy, and agreement between the surgeons' severity rankings and the fracture energy metric was tested by computing their concordance, a statistical measure that estimates the probability that any 2 cases would be ranked with the same ordering by 2 different raters or methods.ResultsConcordance between the 6 orthopaedic surgeons ranged from 82% to 93%, and concordance between surgeon severity rankings and the computed fracture energy ranged from 73% to 78%.ConclusionsThere is a high level of agreement between experienced surgeons in their assessments of tibial plateau fracture severity, and a slightly lower agreement between the surgeon assessments and an objective CT-based metric of fracture energy. Taken together, these results suggest that experienced surgeons share a similar understanding of what makes a tibial plateau fracture more or less severe, and an objective CT-based metric of fracture energy captures much but not all of that information. Further research is ongoing to characterize the relationship between surgeon assessments of severity, fracture energy, and the eventual clinical outcomes for patients with fractures of the tibial plateau

Evaluation of Automated Coverage and Distance Mapping Selections to Improve Reliability and Clinical Utility of 3D Weightbearing CT Assessments

Category: Other; Hindfoot Introduction/Purpose: Progressive collapsing foot deformity (PCFD) is a complex three-dimensional (3D) deformity where adjacent structures may adopt subtle differences in positioning that result in increased contact or subluxation. Recent studies have highlighted the need for and utility of 3D analyses in PCFD using weightbearing CT (WBCT) and bone segmentation. Beyond the limitations of triplanar imaging, 3D distance and coverage mapping analyses have further highlighted key regional differences like sinus tarsi narrowing ahead of impingement and early middle facet uncoverage ahead of collapse. However, these analyses rely upon manual identification of subregions hindering the utility of 3D mapping clinically. The objective of this study was to compare an automated selection process with manual selections in the context of subtalar regional distance and coverage maps in PCFD. Methods: In this IRB-approved retrospective study, WBCT data of 20 consecutive patients with flexible PCFD and 10 controls were analyzed. Subregions of the peritalar surface (middle and posterior facets of the calcaneus and talus; sinus tarsi area) were manually selected by two experts on manually generated bone surfaces of all 30 feet. An automated algorithm for selecting coverage area was applied to identify the same regions on the semi-automatically generated bones (Figure). A 3D distance mapping (DM) technique was used to create coverage maps (CMs) across the entire peritalar surface where areas with distances less than 4mm were defined as covered. DM and CM percentages were compared using intra-class correlations and t-tests between PCFD and control groups. The Sørensen–Dice index, or Dice coefficient, was used for comparisons of selections on the semi-automated surfaces to evaluate reproducibility of expert selections. Results: The automated process produced identical selections resulting in perfect intra-method ICCs of 1.00 for all regions and Dice coefficients of 1.00. The average Dice coefficient for all manual selections was 0.903 (range: 0.865-0.935) indicating that observers were able to reliably select the same regions with 90% overlap. When assessing reliability of manual selections, intra- observer ICCs ranged from 0.41-0.92 while inter-observer ICCs ranged from 0.47-0.99 were found. Despite strong significant correlations, average coverage was significantly lower in the sinus tarsi region of the automated selections vs the manual selections (34.3±16.8% vs 23.1±12.7%, p< 0.005). However, mean distances in each region were not significantly different in the middle facet or the sinus tarsi regions (p=0.323, p=0.095, respectively). Conclusion: Understanding of the complex 3D deformities that constitute PCFD requires sensitive and reproducible measures. Fully automated 3D assessments of coverage and bone relations can help improve understanding these deformities aiding in diagnosis, staging, and objective evaluation of treatment effects. Prior work with this method has specifically identified the middle facet and sinus tarsi regions as being of particular importance. Compared to manual selections, these regions were well identified by the automated process. This represents a major step toward viable use of fully automated 3D coverage and distance mapping when evaluating PCFD patients

Objective Analysis of Regional Tibiotalar Joint Changes in Ankle Osteoarthritis Assessed by Semi- Automated 3D Distance Mapping

Category: Ankle Arthritis; Ankle Introduction/Purpose: Ankle osteoarthritis is a degenerative joint disease characterized by the narrowing of the tibiotalar joint space and in late stages, eventual tibiotalar contact and subchondral bone loss. Traditional methods of assessing changes in the joint space (such as assessment on 2D radiographs) are subjective and do not fully consider the three-dimensional nature of articular surfaces. Weight-bearing CT (WBCT) provides a unique perspective by placing the joints of the lower extremity in a loaded, functional position, and may help to better quantify changes in joint space. Determining the presence and progression of ankle arthritis is difficult. It is our hope that novel 3D distance mapping technologies using images acquired from WBCT may assist with the detection and characterization of progression of ankle osteoarthritis. Methods: In this IRB-approved, retrospective case-control study, we analyzed WBCT data of 9 ankle osteoarthritis patients and 20 healthy controls. Patients included in this study had no identifiable talar tilt. Segmentations were created using an automated segmentation software package (DISIOR Bonelogic 2.0) Principal component analysis was used to divide the talar dome into nine subregions. The articular facet of the medial malleolus was also analyzed. We used 3D distance mapping to objectively measure joint space width across the tibiotalar joint and assessed changes in distance in each of the nine subregions of the talar dome articular surface. Overall mean distances for each subregion analyzed were calculated. Comparisons between the control and ankle arthritis cases were performed with independent t-tests, assuming unequal variances. P-values < 0.05 were considered significant. Results: Changes in the mean distances are reported in the attached figure. The medial side of the talar experienced significant decreases in mean joint space width. The middle medial subregion experienced the largest decrease in mean joint space width with a reduction of 35% when compared to controls (p = 0.017). Increases in joint space width were observed on the lateral aspect of the talar dome, However, these increases were not found to be significant. Conclusion: The purpose of this study is twofold: to quantify changes in joint space using 3D distance mapping technique and to evaluate the utility of a commercial automated segmentation software package. In this cohort, there was a significant decrease on the medial side of the talar dome – this change can be attributed to cartilage degeneration. To our knowledge, this is the first study to analyze changes in ankle osteoarthritis using a fully automated segmentation method. Automated segmentation and 3D distance mapping provide a useful tool for the quantification of osteoarthritis-associated joint space changes

Efficacy of the Ponseti Technique in Correcting Clubfoot Deformity and Influence of Residual Deformity in Patient Reported Outcomes: A Prospective Comparative and Controlled Study

Category: Other; Hindfoot Introduction/Purpose: Clubfoot deformity (CFD) is one of the most common congenital deformities of the foot and ankle and is characterized by different severities of foot equinus, cavus, varus, and adduction. The gold-standard treatment is the Ponseti technique, characterized by serial casting and an Achilles tenotomy. Few studies have assessed long-term outcomes of this treatment, and none have utilized three-dimensional (3D) weightbearing analysis of residual CFD. The goals of this study were to elucidate residual 3D foot deformities in CFD patients treated with the Ponseti technique and to compare them with healthy controls. We also aimed to assess how these deformities influenced patient-reported outcomes (PROs). We hypothesized that significant residual deformities would be observed in CFD patients and that these deformities would negatively impact PROs. Methods: IRB-approved, prospective, comparative, and controlled study. We recruited 37 CFD patients (57 feet) treated with the Ponseti technique that had no additional foot and ankle surgical procedures. We also included 14 healthy control volunteers (28 feet) with no history of foot/ankle injuries/deformities. All patients underwent WBCT imaging (CurveBeam, HiRise). Tarsal bones were semi-automatically segmented (Bonelogic ® , Disior), and several automatic measurements assessing cavus, varus, adductus, and overall 3D deformity (Foot and Ankle Offset – FAO) were performed. Measurements were then correlated with PROs, which included Visual Analogue Scale for pain, PROMIS general health, PROMIS physical function and pain interference, pain catastrophizing scale (PCS), and European Foot and Ankle Society (EFAS) score. Paired T-tests or Paired Wilcoxon were utilized to compare measurements between CFD patients and controls, depending on normality distribution. A multivariate regression analysis assessed the relationship between residual deformities and PROs in CFD patients. P-values < 0.05 were considered significant. Results: No significant overall residual 3D-deformity was found, with similar FAO measurements in CFD and controls (respectively, 2.63% and 3.2%/P=0.58). Slight cavus overcorrection was observed in CFD, with sagittal plane talus-first metatarsal angle of -0.12° versus -5.2o (p=0.04) and calcaneal inclination angle of 13.01° versus 21.5°, respectively. Varus under-correction was identified in CFD patients, with decreased sagittal and axial talocalcaneal angles (44.3o vs. 57.5o/p < 0.0001 and 17.7o vs. 25.78o/p=0.0012, respectively). Similarly, adductus under-correction was observed in CFD, with talonavicular coverage angle 18.63o vs. 29.19o (p < 0.0001). In the multivariate regression analysis, cavus overcorrection (sagittal talus-first metatarsal angle) was the only deformity influencing VAS (R2=0.19/P=0.02) and EFAS-Scores (R2=0.27/p=0.002). Residual varus deformity (sagittal plane talocalcaneal angle) was the only deformity influencing PROMIS Pain Interference (R2=0.14/p=0.038) and Physical Function (R2=0.32/p=0.0007). Conclusion: This study highlights the efficacy of the Ponseti technique in treating the overall 3D foot and ankle deformity in CFD patients, realigning the ankle joint and the weightbearing foot tripod. However, residual CFD components were identified, including overcorrection of the cavus and under-correction of the adductus and varus deformities. Overcorrection of the cavus negatively influenced VAS pain and EFAS scores, and under-correction of the varus negatively influenced PROMIS scores. The results of this study could potentially guide CFD treatment with the Ponseti technique, with focus on improved correction of the varus and avoidance of overcorrection of the cavus deformities

Quantification of First Metatarsal Joint Surface Interactions in Hallux Rigidus Using Distance and Coverage Mapping

Category: Other; Midfoot/Forefoot Introduction/Purpose: WBCT provides anatomical imaging that allows for extraction of metrics characterizing three-dimensional (3D) joint surface interactions. Three-dimensional (3D) Distance-Mapping (DM) and Coverage-Mapping (CM) use WBCT images to evaluate multiplanar elements of Hallux Rigidus (HR) through analyzing joint space and joint coverage across entire bony interfaces. Previous methods have struggled to characterize reliable assessment of these deformity patterns is essential in guiding HR treatment and impacts recurrence rates following correction. The objective was to (1) develop a 3D WBCT CM and DM algorithm to characterize the surface interaction of the 1st metatarsophalangeal-joint (MTPJ) and metatarsal-sesamoid joints (MTSJ) in HR patients and controls (2) correlate DM and CM with Body-Mass-Index (BMI), Coughlin and Shurnas classification- score (CGS), and pre-operative Visual-Analog-Scale (VAS). Methods: Retrospective case-control-study with Forty-one patients (20 HR and 21 controls). Semi-automatic segmentation protocol extracted bone models, which were analyzed with specialized-software. The 1st-MTPJ-surface was divided into two-by- two grids to provide a more detailed analysis. Distance measurements obtained were used to create color-coded distance maps. Blue color was represented expected distances in joint interaction (1 to 5 mm), red or yellow color represented arthritis or impingement (0 to 1mm), and pink color represented subluxation (>5mm). Further, color-coded coverage maps highlighted areas of relative coverage( 5mm) contrasting areas with normal joint interaction or subluxation (Figure). Pearson correlations were computed between mapping metrics and the following for HR patients: Body-Mass-Index (BMI), Coughlin and Shurnas classification-score (CGS), and pre-operative Visual-Analog-Scale (VAS). Intraclass correlation coefficients (ICCs) were calculated to evaluate the interobserver reliability of the CCA selections and CGS obtained by two raters. One rater’s CCA selections and CGS were used for analysis. Results: HR patients displayed joint space narrowing at the first MTP joint when compared to controls (difference in means (DIM) = -11.8%,p=0.02). Quadrant analysis revealed first MTP joint space narrowing in HR patients for the plantar medial quadrant (DIM = -16.8%,p=0.002). Overall coverage in first MTPJ interaction for HR was increased, but not significant compared to controls (DIM = 9.2%,p=0.084). Quadrant analysis revealed increased coverage in first MTP joint surface-to-surface interaction for the plantar medial quadrant of the first metatarsal head (DIM = 13.7%,p=0.005) in HR patients when compared to controls. BMI was moderately positively correlated with mean first metatarsal head JSW (Joint space width) in HR patients (r=0.552,p=0.011). CGS was negatively correlated with mean first metatarsal head JSW for the HR cohort (r= -0.534,p=0.015). Conclusion: We developed a quantifiable WBCT distance and coverage map algorithm to assess 3D joint interaction, joint coverage, and subluxation in patients with HR. Compared to healthy controls, HR patients had increased joint space narrowing at the first metatarsal joint, both overall and specifically at the plantar medial aspect of the joint. Significantly increased coverage at the plantar medial quadrant was also observed in HR patients. Significant narrowing was not observed at the MTSJ. We found a significant correlation between Distance/Coverage mapping, Body-Mass-Index, and Coughlin and Shurnas classification score