Redefining the anatomy of the anterior tibialis tendon.

The observation that, when performing a split anterior tibialis tendon transfer, a twist develops as the distal segment is brought into position on the lateral side of the foot led to our hypothesis that, as a consequence of foot rotation during embryologic development, rotation of the tendon of the anterior tibialis muscle also occurs and can be seen in the adult. Ten unembalmed human lower extremities were examined with regard to the macrostructure of the anterior tibialis tendon. In all 10 specimens, the fibers rotated through 90 degrees from the musculotendinous junction to the insertion on the first cuneiform and metatarsal. The tendon was then split, releasing the first metatarsal insertion in five specimens and the first cuneiform insertion in five. Lateral transfer of the first metatarsal-released group produced a crossing over proximally of the tendon as the fibers came from the medial side of the musculotendinous junction. Lateral transfer of the first cuneiform-released group produced no crossing over proximally as the fibers came from the lateral side of the musculotendinous junction. During a split anterior tibialis tendon transfer, release of the cuneiform insertion will avoid the proximal twisting seen with first metatarsal release and allows for a more direct line of pull of the muscle on the tendon.