The shape of the lateral edge of the first metatarsal head as a risk factor for recurrence of hallux valgus.

BACKGROUND The relationship between the shape of the first metatarsal head and hallux valgus deformity remains controversial. The purpose of the present study was to retrospectively analyze differences in the radiographic appearance of the shape of the lateral edge of the first metatarsal head between women with normal feet and those with hallux valgus and to clarify the relationship between the shape of the lateral edge and the postoperative recurrence of hallux valgus deformity. METHODS Dorsoplantar weight-bearing radiographs of sixty normal feet in women (the control group) and sixty feet in women with hallux valgus (the hallux valgus group) were reviewed. The feet in the hallux valgus group were treated with a proximal metatarsal osteotomy, and the radiographs of those feet were assessed preoperatively, at the time of early follow-up (mean, 3.4 months), and at the time of the most recent follow-up (mean, forty-eight months). The shape of the lateral edge, which was defined as consisting of the articular and lateral surfaces of the first metatarsal head, was examined. The shape of the lateral edge was classified as one of three types: round (type R), angular (type A), and intermediate (type I). We defined the round sign as being positive when the shape of the lateral edge was classified as type R. RESULTS Prior to surgery, the prevalence of the type-R shape was significantly greater in the hallux valgus group than it was in the control group (78.3% compared with 1.7%; p < 0.0001) and the prevalence of type-A shape was significantly lower in the hallux valgus group than in the control group (3.3% compared with 81.7%; p < 0.0001). In the hallux valgus group, the prevalence of the type-R shape at the time of the early follow-up after surgery was significantly lower than that before surgery (p < 0.0001). Feet with a positive round sign at the time of the early follow-up had a greater risk of having recurrence of the hallux valgus deformity at the time of the most recent follow-up than did those without a round sign at the time of the early follow-up (odds ratio, 12.71; 95% confidence interval, 3.21 to 50.36). CONCLUSIONS There is a significant relationship between a round-shaped lateral edge of the first metatarsal head and hallux valgus, and a positive round sign after a proximal first metatarsal osteotomy can be a risk factor for the recurrence of hallux valgus.