Biomechanical study on tibialis posterior tendon transfers.

Two methods are used to route the tibialis posterior tendon anteriorly to achieve dorsiflexion: (1) around the medial side of the tibia, or the subcutaneous route; and (2) through the interosseous membrane, or the interosseous route. This study determined the effect of site of tendon insertion on ankle and foot motions and compared the efficacy of both routes. Eleven fresh normal cadaveric legs were used. The detached tibialis posterior tendon was transferred anteriorly through the interosseous membrane and anchored to the first cuneiform along the first metatarsal axis by a barbed staple. The specimen was mounted on a mechanical testing machine. Tension was applied to the tendon and ankle and foot motions were measured. The experimental procedure was repeated with tendon insertion along the second metatarsal axis and serially through to the fifth metatarsal axis. The entire experiment was repeated using the subcutaneous route. The interosseous route was more effective in achieving maximum dorsiflexion with minimal pronation. Shifting the insertion medially caused supination, whereas a more lateral insertion caused pronation.