Weightbearing Computed Tomography and 3-Dimensional Analysis of Mobility Changes of the First Ray After Proximal Oblique Osteotomy for Hallux Valgus

Background: Hypermobility of the first ray has been evaluated using various methods and has conventionally been considered to be involved in the pathology of hallux valgus. We hypothesized that hypermobility of the first ray in hallux valgus could be decreased by simply correcting foot alignment without arthrodesis. This study sought to evaluate first-ray mobility using weightbearing computed tomography (CT) before and after proximal oblique osteotomy and also in healthy volunteer’s feet. Methods: Subjects were 11 feet of 11 patients with primary hallux valgus who underwent surgery with a plantarly applied anatomic precontoured locking plate and 22 feet of 11 matched healthy volunteers. We performed nonweightbearing and weightbearing (using a load equivalent to body weight) CT scans using an original loading device preoperatively and 1-1.5 years postoperatively. Three-dimensional displacement of the distal bone relative to the proximal bone was quantified for each joint of the first ray by comparing nonweightbearing and weightbearing CT images. Results: At baseline, there were significant differences in hallux valgus angle (P <.001) and 1-2 intermetatarsal angle (P <.001) between healthy volunteer’s feet and preoperative hallux valgus feet. Hallux valgus angle (P <.001) and 1-2 intermetatarsal angle (P <.001) differed significantly between before and after surgery. All first ray joint displacement under loading decreased postoperatively to within 2° of that in healthy volunteer’s feet and showed no significant difference between postoperatively hallux valgus feet and healthy volunteer’s feet (P >.05). Conclusions: We found that first metatarsal osteotomy even without arthrodesis corrected deformity and decreased mobility of the first ray after hallux valgus surgery. Level of Evidence: Level III, case-control study.