Abstract
Research Type:
Level 3 - Retrospective cohort study, Case-control study, Meta-analysis of Level 3 studies
Introduction/Purpose:
Conventional radiographic (CR) assessment has traditionally been used to stage Hallux Rigidus (HR), guiding treatment decisions. Recently, Distance mapping (DM) and Coverage mapping (CM) from weight-bearing computed tomography (WBCT) have emerged as precise tools for obtaining detailed insights into articular surfaces. This study aimed to investigate three-dimensional variations across the Coughlin and Shurnas classification (CSC) grades and propose a new classification based on the findings.
Methods:
This retrospective study included 68 feet: 48 with hallux rigidus (HR) and 20 controls (CSC grade 0). Patients with a first metatarsal-proximal phalanx angle (hallux valgus angle) >15° were excluded. CSC grading was assessed using standing radiographs. Metatarsus primus elevatus (MPE) was measured on weight-bearing CT (WBCT) following a validated method. WBCT scans were segmented semi-automatically to generate 3D models.The first metatarsophalangeal joint (MTPJ) was divided into four quadrants: dorsal medial, dorsal lateral, plantar medial, and plantar lateral. Distance mapping (DM) and coverage mapping (CM) were analyzed at the first MTPJ, and sesamoids. Normality was assessed using the Shapiro-Wilk test. Based on the results, differences in MPE, DM and CM across quadrants and CSC grades were compared using either One-Way ANOVA or Kruskal-Wallis. Partition analysis identified threshold values and patterns of DM variation across CSC grades.
Results:
First MTP DM on average decreased from grade 0 to 2, then increased in grade 3. However, only the plantar-lateral quadrant showed a consistent decline (p < .05). DM in both sesamoids decreased from grade 0 to 1 (p < .05) but increased from grade 2 to 3. CM of the first MTPJ increased across grades (39.9%, 41.0%, 45.2%, 51.0%). MPE was higher in pathological grades (4.47 mm) than controls (3.22 mm, p = .0251), though differences among grades 1 to 3 were not significant. Partition analysis identified the plantar-lateral quadrant as the best predictor of HR severity, with DM >1.574 mm linked to grade 0 or 1, while all grade 2 or 3 cases had lower values.
Conclusion:
Metatarsal-sesamoid joint narrowing and MPE differed significantly between grade 0 and pathological cases but among grades 1 to 3, suggesting they do not progress in parallel with first MTPJ narrowing. First MTPJ narrowing is best observed in the plantar-lateral quadrant, with a 1.574mm threshold distinguishing moderate from severe cases. The lack of significant differences in DM and CM between grades 2 and 3 suggests that these grades could be merged, supporting a simplified classification based on DM: grade 0 (no changes), grade 1 (mild changes), and grade 2 (severe changes). Further studies are needed to validate this classification clinically.
