Anatomic Comparison of Lateral Transfer of the Long Flexors for Concomitant Peroneal Tears

Abstract

Lateral transfers of the flexor hallucis longus (FHL) or flexor digitorum longus (FDL) tendons have been described for treatment of concomitant, irreparable peroneal tears. This study evaluated the anatomic benefits and constraints of lateral FHL and FDL tendon transfers with regard to available tendon length, diameter, and proximity to the posterior neurovascular bundle. In 9 cadaveric specimens, the FHL and FDL tendons were transected through a medial approach distal to the knot of Henry. Each tendon was transferred into a lateral incision, passing the FDL tendon both posterior and anterior to the tibial neurovascular bundle. The tendons were individually secured to the base of the fifth metatarsal with the foot in maximal eversion and dorsiflexion. The length of donor tendon available for fixation at the fifth metatarsal was measured. After the FDL tendon transfer was secured, the posterior neurovascular bundle was examined for signs of compression. Average FHL tendon diameter measured 5.1 mm; the FDL measured 4.5 mm. After passage through a bone tunnel, an additional 4.9 cm of FHL tendon remained to suture to itself; only 0.5 cm remained for the posterior and anterior FDL transfers. Transfer of the FHL did not increase muscle bulk within the retrofibular groove. Every FDL transfer posterior to the neurovascular bundle produced obvious visual compression of the tibial nerve with plantar flexion and inversion of the foot. Use of the FHL tendon for lateral transfer consistently provided sufficient length of tendon for multiple fixation options and a stronger muscle for transfer. Fixation options for the FDL were limited due to its shorter length. Lateral transfer of the FDL tendon posterior to the neurovascular bundle caused visible compression on the tibial nerve with ankle and hindfoot range of motion. This anatomic study confirmed several advantages for the use of the FHL tendon transfer in cases of concomitant peroneal tears.