Study Aim

To design an educational resource for people with lower back pain (LBP) using creative co-production.

Background: Neglected ruptures of the tendoachilles pose a difficult surgical problem. Intervening scar tissue has to be excised which cannot be repaired by end-to-end anastamosis. Several techniques for reconstruction of chronic ruptures have been described. The flexor hallucis longus (FHL) tendon transfer is considered advantageous over other tendon transfers. One disadvantage of FHL is it has limited excursion. There are no data to determine the optimal positioning of the FHL tendon to the calcaneum.

Materials and Methods: Two computer programmes (MSC.visualNastran Desktop 2002™ and Solid Edge® V19 were used to generate a human ankle joint model. This model is able to reproduce dorsi- and plantarflexion. Different attachment points of FHL tendon transfer to the calcaneum were investigated.

Results: The lowest muscle force to produce plantarflexion (single stance heel rise) was 1355N. Plantarflexion increased for a more anterior attachment point. The maximal plantarflexion was 33.4° for anterior attachment and 24.4° for posterior attachment. There was no significant difference in these figures when the attachment point was moved to either a medial or lateral position.

Clinical relevance: Optimal FHL tendon transfer positioning is a compromise between achieving plantarflexion for normal physiological function versus the force generating capacity and limited excursion of FHL. A more posterior attachment point is advantageous in terms of power. The range of motion is 10° less than when attachment is more anterior, the arc of motion (24.4°) is still physiological. We recommend that FHL is transferred to the calcaneum in a posterior position.