Extensor Tendon Transfers for Treatment of Foot Drop in Charcot-Marie-Tooth Disease: A Biomechanical Evaluation

Abstract

Category: Midfoot/Forefoot; Ankle; Lesser Toes; Other Introduction/Purpose: Transfer of the Extensor hallucis longus (EHL) and extensor digitorum longus (EDL) tendons is an underutilized procedure for the treatment of drop foot in patients with Charcot-Marie-Tooth disease (CMT). Transfer of these tendons should be considered for augmentation of ankle dorsiflexion in the CMT population, regardless of the presence of clawed toes. The preferred site for tendon transfer, however, remains unknown. We hypothesized that EHL/EDL transfers will improve ankle dorsiflexion compared to the intact state but will produce similar motion at either the metatarsal necks or cuneiforms. Methods: Eight fresh-frozen cadaveric specimens transected at the mid-tibia were mounted into a specialized jig with the ankle held in 20 degrees of plantarflexion. The EHL and EDL tendons were isolated and connected to linear actuators with suture. Diodes secured on the 1st metatarsal, 5th metatarsal and tibia provided optical data for tibiopedal position in 3-dimensions. After preloading, the tendons were tested at 25%, 50%, 75% and 100% of maximal physiologic force for the EHL and EDL muscles, individually and combined. Results: Transfers to metatarsal and cuneiform locations significantly improved ankle dorsiflexion compared to the intact state. No difference was observed between these transfer sites. Following transfer, only 25% of maximal force by combined EHL and EDL was required to achieve a neutral foot position. Conclusion: Transfer of the long toe extensors, into either the metatarsals or cuneiforms, significantly increases dorsiflexion of the ankle. Transfer should be considered for augmentation of dorsiflexion in the CMT population, regardless of the presence of clawed toes. This study supports tendon transfers into the cuneiforms, which involves less time, fewer steps and easier tendon balancing without compromising dorsiflexion power.