Quantification of First Metatarsal Joint Surface Interactions in Hallux Rigidus Using Distance and Coverage Mapping
Authors: Jones Matthew T. , Carvalho Kepler A.M. , Mallavarapu Vineel , Behrens Andrew , Braza Samuel , Schmidt Eli , Talaski Grayson M. , Dibbern Kevin , Mansur Nacime Salomao Barbachan , de Cesar Netto Cesar 
Published: December 2023

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) or uncoverage(>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.