Does ankle arthrodesis induce satisfactory changes in the medial longitudinal arch height of the foot for severe varus ankle arthritis?

Purpose We designed this study to determine how changes in coronal ankle alignment affect sagittal alignment of the foot. Specifically, we focused on the changes in medial longitudinal arch height, which could be reflected by the medial cuneiform height (MCH), Meary's angle, and calcaneal pitch angle (CPA). Methods We retrospectively analyzed the radiographic findings of 37 patients who underwent open ankle arthrodesis without inframalleolar correction (such as first metatarsal dorsal closing wedge osteotomy, calcaneal osteotomies, tendon transfers, or tarsal joint arthrodesis) of severe varus ankle arthritis. The inclusion criterion was a pre-operative tibial axis to talar dome angle of 80 degrees or less. The enrolled patients were divided into two groups according to the post-operative decrease in MCH (<= 2 mm or < 2 mm). Results A post-operative MCH decrease of <= 2 mm was observed in 43.2% (16 patients). Although the degree of coronal ankle varus correction was similar, the decrease in the Meary's angle was significantly greater in the group with a post-operative MCH decrease of <= 2 mm than in those with < 2 mm (- 4.1 degrees vs. - 1.3 degrees, P = 0.01). The changes in CPA were not significantly different (P = 0.172). Conclusion Correction of ankle varus deformity via ankle arthrodesis could lead to a decrease in the medial longitudinal arch height in less than half of the enrolled patients. In these patients, a cavus component of the foot might be an important factor in determining a successful sagittal foot alignment change, while the CPA was maintained post-operatively.