Chronic tenosynovitis (either traumatic, degenerative, or secondary to inflammatory arthritis), loss of continuity of the tendon (either complete or incomplete), and loss of the normal anatomic relationships of the tendon to its insertion or insertions (the accessory navicular) may render the posterior tibial tendon insufficient to perform its tasks of plantar-flexion, inversion, and stabilization of the medial longitudinal arch. For this reason, the term insufficiency of the posterior tibial tendon is descriptive. Further classification according to the just-mentioned etiologic factors is necessary for communicating the pathologic findings of this essential tendon of the foot. Other than the Achilles tendon, no other muscle-tendon unit distal to the knee can cause as many symptoms and functional deficits as loss of the posterior tibial tendon.
