Determination of optimal screw positioning in flexor hallucis longus tendon transfer for chronic tendoachilles rupture

BackgroundNeglected ruptures of the tendoachilles pose a difficult surgical problem. There are no data to determine the optimal positioning of the FHL tendon to the calcaneus.MethodsTwo computer programmes (MSC.visualNastran Desktop 2002™ and Solid Edge® V19) were used to generate a human ankle joint model. Different attachment points of FHL tendon transfer to the calcaneus were investigated.ResultsThe lowest muscle force to produce plantarflexion (single stance heel rise) was 1355 N. Plantarflexion increased for a more anterior attachment point. The maximum range of plantarflexion was 33.4° for anterior attachment and 24.4° for posterior attachment. There was no significant difference in range of movement when the attachment point was moved to either a medial or lateral position.ConclusionsA more posterior attachment point is advantageous in terms of power and the arc of motion (24.4°) is physiological. We recommend that FHL is transferred to the calcaneus in a posterior position.