The Role of First Tarsometatarsal Joint Morphology and Instability in the Etiology of Hallux Valgus: A Case-Control Study

Category: Midfoot/Forefoot; Bunion Introduction/Purpose: The morphology of foot joints is believed to significantly impact the development of various foot disorders. The relationship of the first tarsometatarsal joint (TMT1) morphology and hallux valgus (HV) is not well understand, and the influence of TMT1 morphology on TMT1 instability has not been fully explored. This study aimed to investigate the TMT1 morphology and its potential correlation with HV and TMT1 instability. Methods: Weightbearing CT (WBCT) scans of 82 consecutive feet with hallux valgus and 79 controls were reviewed in this case-control study. Using Mimics software and WBCT scans, the three-dimensional (3D) models of TMT1 were constructed. The height of the TMT1 facet (FH), superior, middle, and inferior facet width (SFW, MFW, and IFW) were measured on anteroposterior view of the first metatarsal base. On the lateral view, the inferior lateral facet height and angle (ILFH and ILFA) were measured. TMT1 instability was evaluated using the TMT1 angle. Results: Compared with the control group, the HV group suggested significantly wider MFW (9.6mm in HV, 8.8mm in control), lower ILFH (1.7mm in HV, 2.5mm in control), smaller ILFA (17.7° in HV, 24.3° in control), and larger TMT1 angle (1.9° in HV, 0.9° in control) (All P < 0.05). No significant differences were found between the two groups in FH, SFW, and IFW (All P > 0.05). Four types of TMT1 (continuous-flat, separated-flat, continuous-protruded, and separated-protruded) were identified according to the TMT1 morphology. The continuous-flat type possessed significantly larger HVA, IMA and TMT1 angles compared with other types (All P < 0.001). Conclusion: This study suggests an association between TMT1 morphology and the severity of HV, and identifies four TMT1 types. Notably, the continuous-flat type is found to be associated with more severe HV and TMT1 instability.