Second Metatarsal Length is Positively Correlated with Increased Pressure and Medial Deviation of the Second Toe in a Robotic Cadaveric Simulation of Gait

Abstract

The term `crossover second toe' has been used to describe a deformity of the second metatarsophalangeal joint (MTPJ) that includes a progressive migration of the second toe in a dorsal and medial direction. The long onset and complex anatomy of the deformity has led to uncertainty about its etiology and treatment. The purpose of this study was to investigate the relationship between second metatarsal length and second MTPJ plantar pressure and joint angles during gait. We hypothesized that elongation of the second metatarsal would increase the plantar pressure underneath the second MTPJ and be associated with a deviation of the MTPJ angles in a dorsal and medial direction. Incremental surgical elongation of the second metatarsal was performed on six cadaveric feet. A robotic gait simulator (RGS) simulated physiologic tibial motion, tendon loading, and ground reaction forces (GRF) on the cadaveric feet. We determined the peak pressure and pressure-time integral under the second MTPJ during gait, as well as the transverse and sagittal MTPJ angles. Second metatarsal peak pressure and pressure-time integral were positively correlated with an increase in second metatarsal length. First metatarsal peak pressure and pressure-time integral were significantly negatively associated with second metatarsal length. MTPJ transverse plane angle was positively associated with second metatarsal length but sagittal angle was not. Our results support the hypothesis that second metatarsal length is positively associated with medial deviation of the second toe and increased plantar pressure underneath the second MTPJ. It is biomechanically plausible that this association could lead to the joint instability seen in crossover toe patients.