Anatomical considerations of posterior tibialis tendon entrapment in irreducible lateral subtalar dislocation.

Irreducible lateral subtalar dislocation is associated with posterior tibialis tendon entrapment. Mulroy and Leitner have proposed conflicting theories regarding the exact mechanism of tendon entrapment. Cadaveric analysis of lateral subtalar dislocation supported Leitner's contention that tearing of the flexor retinaculum promotes posterior tibialis tendon entrapment. Retinacular disruption allowed tendon subluxation over the medial malleolus and talar head to the entrapped position. Entrapment of the flexor digitorum longus only occurred in the Leitner model. When the flexor retinaculum and deep posterior compartment fascia were preserved, the muscle failed at the musculotendinous junction. Flexor hallucis longus entrapment could not be produced in either experimental model. Plantarflexion of the great and lesser toes, noted on clinical presentation, is caused by functional lengthening of the route coursed by the flexor digitorum longus and flexor hallucis longus.