Moberg Osteotomy Shifts Contact Pressure Plantarly in the First Metatarsophalangeal Joint in a Biomechanical Model.

Abstract

A proximal phalangeal dorsiflexion osteotomy (Moberg osteotomy) is commonly used to treat hallux rigidus, but the mechanical explanation for its effectiveness is unclear. The purpose of our study was to test the effect of a Moberg osteotomy on first metatarsophalangeal joint contact mechanics. Ten cadaveric first ray specimens were dissected, with the medial band of the plantar aponeurosis preserved at its origin, and placed in a custom testing apparatus. Forefoot loads during mid-stance with the first metatarsal positioned at 10 degrees were simulated using a custom-made loading jig while contact mechanics were acquired with a thin pressure-sensitive sensor. A Moberg osteotomy was performed starting 9 mm distal to the proximal phalanx with excision of a 3-mm wedge of bone and fixated with a 2-mm Kirschner wire. The effect of the Moberg osteotomy was tested by reapplying the forefoot loads and acquiring the joint pressures. The center of pressure, peak pressure, and contact area were calculated. Paired t tests were performed to determine if the Moberg osteotomy affected joint contact mechanics. The Moberg osteotomy shifted the center of contact pressure on the proximal phalanx surface more plantarly (P < .01). However, the Moberg osteotomy did not affect the peak pressure (P = .62) or the joint contact area (P = .96). There were no differences in peak pressure or first MTPJ contact area, but a plantar shift in the center of pressure occurred after the Moberg osteotomy. The plantar cartilage, which is often spared from arthritic changes, may be preferentially loaded and the potential edge loading following cheilectomy may be avoided with the Moberg osteotomy secondary to the plantar shift of center of pressure.