[Injuries and dysfunction of the posterior tibial tendon]

The function of the posterior tibial (PT) tendon is to stabilize the hindfoot against valgus and eversion forces. It functions as the primary invertor of the foot and assists the Achilles tendon in plantar flexion. The PT tendon is a stance phase muscle, firing from heel strike to shortly after heel lift-off. It decelerates subtalar joint pronation after heel contact. It functions as a powerful subtalar joint supinator and as a support of the medial longitudinal arch. The action of the tendon travels to the transverse tarsal joints, locking them and allowing the gastrocnemius to support heel rise. Acute injuries of the PT tendon are rare and mostly affect the active middle-aged patient or they are the result of complex injuries to the ankle joint complex. Dysfunction of the PT tendon following degeneration and rupture, in contrast, has shown an increasing incidence in recent years. To which extent changed lifestyle, advancing age, comorbidities, and obesity play a role has not yet been clarified in detail. Dysfunction of the PT tendon results in progressive destabilization of the hind- and midfoot. Clinically, the ongoing deformation of the foot can be classified into four stages: in stage 1, the deformity is distinct and fully correctable; in stage II, the deformity is obvious, but still correctable; in stage III, the deformity has become stiff; and in stage IV, the ankle joint is also involved in the deformity. Treatment modalities depend on stage: while conservative measures may work in stage I, surgical treatment is mandatory for the later stages. Reconstructive surgery is advised in stage II, whereas in stage III and IV correcting and stabilizing arthrodeses are advised. A promising treatment option for stage IV may be adding an ankle prosthesis to a triple arthrodesis, as long as the remaining competence of the deltoid ligament is sufficient. An appropriate treatment is mandatory to avoid further destabilization and deformation of the foot. Failures of treatment result mostly from underestimation of the problem or insufficient treatment of existing instability and deformity.