Effect of First Metatarsal Shortening and Dorsiflexion Osteotomies on Forefoot Plantar Pressure in a Cadaver Model

Abstract

Background: Metatarsalgia of the second ray is a common problem associated with disorders of the first metatarsal. It also occurs after the operative treatment of those disorders. Plantar pressure changes from alteration of the static and dynamic structure of the forefoot may be associated with this condition. This study evaluated changes in plantar forefoot pressure especially under the second metatarsal head after three operative procedures on the first ray. Methods: Each of 12 cadaver foot specimens was cyclically loaded on the servohydraulic MTS Mini Bionix test frame (MTS Systems Corp., Eden Prairie, MN) with traction on the Achilles tendon. Plantar forefoot pressure was measured by the F-scan system (Tekscan, Inc., S. Boston, MA) with the foot intact, after a first metatarsal base dorsal closing-wedge osteotomy with 5-mm base length to simulate dorsal malunion, and after 5-mm and 10-mm metatarsal shortening procedures. Paired Student t-test analysis was used to compare data for the intact foot with data after each intervention. One form of Bonferroni's correction was done to establish a new alpha level to tighten the analysis and to compensate for multiple paired Student t-tests. The significance level was calculated to be 0.016 based on an original alpha level of 0.05. Results: As compared with the intact foot, all three procedures on the first metatarsal resulted in significant decreases in plantar pressure under the first metatarsal head ( p < 0.016). Plantar pressure under the second metatarsal head increased significantly as compared with the intact foot ( p < 0.016) after all three procedures. Pressures under the third-fourth metatarsal heads increased significantly compared with the intact foot after the 5-mm and 10-mm shortenings ( p < 0.016). Plantar pressure under the fifth metatarsal did not change significantly after any of the three procedures. Conclusions: Dorsiflexion osteotomy and shortening of the first metatarsal are associated with significant forefoot plantar pressure changes in a cadaver model.