Investigating the Relationship Between Metatarsal Primus Elevatus and Hallux Rigidus Using Weight-Bearing Computed Tomography: A Retrospective Comparison Study.

BACKGROUND

Hallux rigidus is a degenerative disease of the first metatarsophalangeal (MTP) joint, characterized by joint space narrowing and dorsal osteophyte formation. Metatarsus primus elevatus (MPE) is frequently observed in hallux rigidus, although its role in the pathogenesis remains unclear. The windlass mechanism, which stabilizes the medial longitudinal arch by tightening the plantar fascia during hallux dorsiflexion, plays a key role in normal foot biomechanics. Dysfunction of this mechanism may result in loss of arch stability and altered loading of the first MTP joint, potentially contributing to the development or progression of hallux rigidus.

METHODS

Eighteen patients (21 feet) with Grade I or II hallux rigidus and 10 healthy volunteers (19 feet) underwent weight-bearing CT. Sagittal images were used to measure the width of the MTP joint space and the deviation of the center of rotation. Image acquisition was performed with the hallux in a minimally dorsiflexed position under static weight-bearing conditions to provide standardized and reproducible comparisons. Comparisons between the groups were performed using t-tests and one-way analysis of variance (ANOVA).

RESULTS

The dorsal joint space was significantly narrower in the hallux rigidus group than in the control group (1.32 ± 0.15 mm vs. 1.88 ± 0.11 mm; P < 0.01). The center of rotation was located in a more plantar position in the hallux rigidus group (-0.39 ± 0.17 mm) compared with the control group (0.51 ± 0.09 mm; P < 0.01). These differences were more pronounced with increasing disease severity, suggesting the early presence of MPE.

CONCLUSIONS

MPE, as defined by a plantar shift in the center of rotation under load, is present from the early stages of hallux rigidus and may disrupt joint congruity and promote cartilage degeneration. These findings support a central role for MPE and failure of the windlass mechanism in the pathogenesis of hallux rigidus.