The Position and Morphology of the Peroneus Longus Tubercle in Hallux Valgus: A Weight-Bearing CT Assessment

CATEGORY: Bunion; Midfoot/Forefoot INTRODUCTION/PURPOSE: The peroneus longus is one of the main dynamic stabilisers of the first ray acting through its primary insertion at the first metatarsal base and has the theoretical possibility to be defunctioned in hallux valgus (HV). In this study, our primary objective was to report and compare the position and morphology of the peroneus longus tubercle (PLT) in feet with and without HV, using weightbearing CT (WBCT). METHODS: A retrospective analysis of WBCT scans was completed using 40 feet in 23 patients. Feet were divided into two equal groups - the normal, 'non-hallux valgus' (non-HV) group and the 'HV' group (Mean age 60.45 and 60.60 respectively). The morphology and position of the PLT was assessed between groups. The intermetatarsal angle (IMA) and metatarsal pronation angle (MPA) were assessed. We also introduce and have assessed the novel measurements of tubercle-to-floor distance (T-F distance), the bisecting angle of the PLT, tubercle-to-metatarsals angle (T-MT angle) as well as the metatarsal cross-sectional area. RESULTS: Between the non-HV group and the HV group, significant differences were found in the T-F distance (mean 26.7mm and 23.35mm respectively, p = .001), illustrating a lower medial column in HV. There was a moderate correlation between IMA and T- F distance (r = -.475, p < .001) confirming depression of the first ray with increasing IMA. The bisecting angle was lower in the HV group as compared to non-HV (mean 61.65 degrees and 66.60 degrees respectively, p=0.017), demonstrating pronation of the PLT in relation to the floor in the HV. We found a significant difference in T-MT angle between the HV and non-HV groups (mean 31.85 degrees and 35.85 degrees respectively, p=0.041) and a strong correlation between the T-MT angle and bisecting angle (r = .817, p< .001) suggesting the pronation occurred in the first metatarsal to a larger degree than the remainder of the forefoot. CONCLUSION: In this study we have demonstrated a difference in the position of the PLT between HV and non-HV individuals, with a pronated PLT noted in individuals with HV.