Torsion of the tendon of tibialis posterior.

The authors present a previously undescribed torsion located within the tendon of tibialis posterior. The musculotendinous unit of tibialis posterior was isolated from 17 lower extremities of cadavers. A small goniometer was constructed and used to quantify the degree of torsion located within each tibialis posterior tendon. Torsion was present in all 17 cadaver specimens, with a mean of 47.5 degrees and a range from 21 degrees to 62 degrees. The regional anatomy and biomechanical functions of tibialis posterior are discussed, and proposed bases for the embryologic origins and functional significance of the torsion are presented.