Three-dimensional Weight-Bearing CT Distance and Coverage Mapping Assessment of the 1st MTPJ and Sesamoid Joints in Patients with Hallux Valgus Deformity
Authors: Mallavarapu Vineel , Carvalho Kepler A.M. , Jasper Ryan , Stebral Hannah J. , Jones Matthew T. , Talaski Grayson M. , Behrens Andrew , Dibbern Kevin , Mansur Nacime Salomao Barbachan , de Cesar Netto Cesar 
Published: December 2023

Category: Bunion Introduction/Purpose: Three-dimensional (3D) Distance-Mapping (DM) and Coverage-Mapping (CM) use WBCT images to evaluate multiplanar elements of Hallux Valgus (HV), such as sesamoid subluxation, through analyzing joint space and joint coverage across entire bony interfaces. Previous methods have struggled to characterize sesamoid subluxation consistently, and the reliable assessment of these deformity patterns is essential in guiding HV 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 in HV patients and controls (2) correlate DM and CM measurements with WBCT semi-automatic angular measurements in HV patients and controls (3) correlate DM, CM, and angular measurements with Visual Analog Scale (VAS) scores in HV patients. Methods: Retrospective case-control study assessing HV patients. 51-feet with HV who underwent a WBCT of the affected foot and 54-feet were included. 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 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’s correlations were used to describe association between intraarticular distances, or JSW (joint space width), and coverage measurements with the following: intermetatarsal angle (IMA), Hallux-Valgus- Angle (HVA), Distal-Metatarsal-Articulation-Angle (DMAA), Visual-Analog-Scale (VAS), and Body-Mass-Index (BMI). P-values less than 0.05 were statistically significant. Results: Interobserver reliability was high for 1st-metatarsal-head (ICC 0.846,p < 0.001), medial-sesamoid-articulation (ICC 0.854,p < 0.001), and lateral-sesamoid-articulation (ICC 0.832,p < 0.001). HV patients demonstrated significantly decreased coverage in comparison to controls (42.7% vs. 50.1%,p < 0.001) and a relative decrease in 1st-MTPJ-coverage (-14.7%,p < 0.001) in comparison to controls. In HV, articular coverage was higher in patients for the plantar lateral quadrant (HV 88.6% vs. 83.0% Controls,p=0.0002) and decreased in dorsal-medial (HV 8.8% vs. 18.7% Controls,p < 0.0001) and plantar-medial quadrants. (HV 46.2% vs. 78.8% Controls,p < 0.0001). Significantly decreased coverage was observed in HV-patients in both the medial sesamoid- articulation (HV 31.1% vs. 54.4%, p< 0.0001) and lateral sesamoid-articulation (HV 22.6% vs. 46.0%,p < 0.0001). Correlations between the first-metatarsal-head distance/coverage measurements and BMI, pre-op VAS, IMA, HVA, and DMAA are summarized in figure. Conclusion: We developed a quantifiable WBCT distance and coverage map algorithm to assess 3D-joint-interaction, joint- coverage, and subluxation in patients with HV. We observed significant subluxation of the 1st-MTPJ in patients with HV when compared to controls, as well as significant subluxation of the metatarsal-sesamoid joint at the medial and lateral sesamoid-joints, with an apparent medial and dorsal deviation of the first-metatarsal, lateral and plantar deviation of the proximal-hallux-phalanx and Lateral subluxation of the sesamoids. Increased coverage of the 1st-metatarsal-head was associated with decreased IMA and DMAA. However, we found no significant correlation between the Visual-Analogue-Scale-(VAS) and DM, CM, and semi-automatic measurements.