Pronation of the First Metatarsal in Hallux Valgus Deformity

Abstract

Category: Bunion Introduction/Purpose: Hallux Valgus is a common condition often resulting in chronic pain and disability. However, the precise etiology of Hallux Valgus deformity remains poorly understood and likely results from a combination of intrinsic and extrinsic factors. There is conflicting evidence regarding as to whether hallux valgus deformity is associated with increased pronation of the first metatarsal. The purpose of this study was to investigate the correlation between hallux valgus and pronation of the first metatarsal in relation to other structural parameters of the foot. Methods: Eighty-five consecutive patients with clinically and radiographically diagnosed hallux valgus, pes planus, or cavovarus that underwent imaging with weightbearing CT between January 2014 and May 2016 were retrospectively enrolled and compared to a control group consisting of patients who with scans completed for indications unrelated to hallux valgus (e.g. ankle arthritis) and were determined to have normal foot structure. Using a weightbearing CT axial view, the alpha angle of the first metatarsal was measured and correlated with other radiographic parameters on plain weightbearing radiographs including Meary’s angle, hallux valgus angle, intermetatarsal angle, and calcaneal pitch. Results: There were 39 males and 46 females (91 feet) with a mean age of 47.16 (SD14.89) years and BMI of 32.99 (SD 7.35) kg/m2 included in this study. Mean pronation of the first metatarsal significantly (p<0.001) different in all group compared to the control: 15.23 (SD 7.96) in the hallux valgus group, 15.22 (SD 8.56) in the pes planus group, negative 0.23 (SD 5.99) in the cavovarus group, and 6.98 (SD 5.09) in the control group. There was moderate correlation between meary’s angle, tripod index, calcaneal pitch, and the alpha angle (negative 0.70, 0.65, negative 0.53, respectively) with a p-value < 0.001. HVA demonstrated little correlation with the measured alpha angle (0.23), p<0.03. Conclusion: Patients with hallux valgus deformity demonstrated a significantly higher pronation of the first metatarsal compared to the control group. However, a greater number of patients in the hallux valgus group had flatfoot deformity and further analysis revealed a greater correlation between foot type and pronation of the first metatarsal. Weightbearing CT is a reasonable way to image complex forefoot deformities prior to bunion surgery and it is important to take into account rotation of the first metatarsal in bunion surgery.