Radiographic Assessment of Transverse Tarsometatarsal Instability Complicated by Metatarsus Adductus in Hallux Valgus Patients

Objective evaluations of transverse tarsometatarsal (TMT) hypermobility/instability are lacking. This study aims to radiographically explore the relationship between transverse TMT instability and metatarsus adductus (MA) in hallux valgus (HV). This study retrospectively analyzed 207 feet with varying degrees of HV, employing the distance between the first and second metatarsals (M1-2 distance) to assess transverse TMT instability of the first ray. Participants were categorized into MA and non-MA groups. It was found that the M1-2 distance significantly increased with the hallux valgus angle (HVA) and metatarsus adductus angle (MAA), demonstrating significant differences between the MA and non-MA groups. The measurement of M1-2 distance showed high reliability, and its cutoff value was determined to be 4.05 mm. Additionally, the results suggest that the widening of the M1-2 distance may be a predisposing factor for MA in HV patients, highlighting its role in the pathogenesis of this foot condition. These findings highlight the need for a comprehensive assessment of TMT instability on both the axial and sagittal planes for the surgical planning of HV, particularly when complicated by a large MAA. Based on these insights, reoriented first-TMT arthrodesis might be recommended for HV with significant MA to address potential multiplanar instability.