Anatomic Basis for Minimally Invasive Flexor Hallucis Longus Transfer in Chronic Achilles Tendon Rupture

The present cadaveric study was designed to measure the flexor hallucis longus (FHL) tendon length and obtain anatomic data regarding the graft-to-tunnel length ratio in an interference screw fixation model for the FHL short-harvest single-incision technique to the calcaneus. Ten fresh-frozen paired cadaveric specimens were used for the FHL short-harvest technique. The length of the osseous tunnel in the calcaneus was measured. At harvesting of the FHL tendon, the length of the tendon that traverses the osseous tunnel was measured with the ankle in neutral and maximal plantarflexion from the tip of the osseous tunnel to the transected end of the tendon within the bone tunnel. The mean length of the osseous tunnel was 42.7 ± 2.3 (range 38 to 46) mm. With the ankle in neutral position, the mean length of the FHL tendon traversing the bone tunnel was 31 ± 1.7 (range 29 to 34) mm. This mean length increased to 38.8 ± 1.6 (range 36 to 41) mm with the ankle placed in maximal plantarflexion. The ratio of the mean length of the tendon graft to the mean length of the osseous tunnel with the ankle in neutral was 0.727 ± 0.046 (range 0.667 to 0.81), and the ratio was 0.91 ± 0.042 (range 0.864 to 0.976) when the ankle was maximally plantarflexed. To the best of our knowledge, we report for the first time that the short-harvest technique provides >70% (ratio 0.727) of the FHL tendon graft in the osseous tunnel at all times, even when then ankle is in neutral, resulting in sufficient tendon length for FHL tendon transfer to the calcaneus for chronic Achilles tendon rupture.