Traumatic forward dislocation of the tibialis posterior tendon is a rare lesion. On the anatomic basis, the pathogenetic mechanism had been suggested to br a hypoplasia of the sulcus for tiblalis posterior tendon. But the bilateral dislocatlons had not been reforted. The injury mechanism was dorsiflexion and internal rotation or inversion of the ankle and foot.

In our case, the tendon itself was not injured but the flexor retinaculum and the perlosteum were detached and elevated from the medial malleolus.

The excellent result has been obtained by simple reattaching procedure of the detached and elevated coverings.

Our study, comparing the depth and the inclinatlon of the sulcus with the normal controls by the CT scanning, showed no valuable anatomic considerations.

We demonstrate the uncommon dislocation of the tibialis posterior tendon, pathogenetic mechanlsms, treatment, and its prognosis.