The Role of Weight-Bearing Computed Tomography Scan in Hallux Valgus

CATEGORY: Midfoot/Forefoot; Bunion INTRODUCTION/PURPOSE: Hyperpronation of the 1st metatarsal in hallux valgus (HV) is poorly understood by conventional weightbearing radiography. We aimed to evaluate this parameter using weightbearing computed tomography (WBCT) and understand its association with other standard measurements. METHODS: Retrospective evaluation of WBCT and weightbearing radiographs (WBXR) was performed for 20 patients with hallux valgus (HV) feet and 20 controls with no such deformity. Axial CT images of both groups were compared for 1st metatarsal pronation angle (α angle) and tibial sesamoid subluxation (TSS) grades. The hallux valgus angle (HVA), first-second intermetatarsal angle (IMA), 1st metatarsal-medial cuneiform angle (MMCA), Meary’s angle, and calcaneal pitch (CP) angle of the study and control groups were compared on both WBXR and the corresponding 2D images of WBCT. All the measurements were independently studied by a dedicated musculoskeletal radiology fellow. RESULTS: HV group demonstrated significantly higher values for TSS grade (p < 0.001) but not for α angle (p = 0.19) compared to controls. Pearson’s correlations of the α angle, in the HV group, revealed no significant linear relationship with TSS grades, IMA and MMCA, and only a moderate positive correlation with HVA as per WBXR (r = 0.38, p = 0.014) but not by WBCT (p = 0.084). Also, α angle performed within the range of a chance (AUC 0.64, 95% CI: 0.49 to 0.66) when measured by receiver operating characteristic (ROC) curves. CONCLUSION: The α angle - a measure of abnormal hyperpronation of the 1st metatarsal - is an independent factor that may co- exist with other parameters in HV, but in isolation has limited diagnostic utility. ‘Abnormal’ α angles may even be observed in individuals without HV deformity. An increase in the HVA, IMA, MMCA or TSS grade is not necessarily associated with a similar increase in the α angle and hence, the severity of HV deformity may not be judged on this parameter alone. The WBCT is a reliable method to assess hyperpronation and guide physicians during surgical management.