The Science of Posterior Tibial Tendon Dysfunction

Posterior tibial tendon dysfunction (PTTD), now commonly termed Progressive Collapsing Foot Deformity (PCFD), represents a complex, progressive condition involving failure of the posterior tibial tendon and associated ligamentous structures. The posterior tibial tendon serves as the primary dynamic stabilizer of the medial longitudinal arch and controls hindfoot motion during the stance phase of walking. The condition begins with inflammation and degenerative changes within the tendon substance (tendinosis), often triggered by repetitive microtrauma or acute overload. As the tendon's structural integrity compromises, its eccentric strength diminishes, particularly during the loading response and terminal stance phases of gait. This leads to progressive loss of the tendon's ability to resist pronation forces and maintain arch integrity. Secondary to tendon failure, supporting ligamentous structures become progressively incompetent. The spring ligament complex (calcaneonavicular ligament) stretches and eventually fails, followed by attenuation of the superficial deltoid ligament, long and short plantar ligaments, and plantar fascia. This cascade creates a characteristic pattern of deformity: hindfoot valgus, forefoot abduction, midfoot collapse, and eventual ankle valgus in advanced cases. The condition progresses through distinct stages: Stage I involves tendinosis without deformity, Stage II presents flexible deformity that corrects with non-weight bearing, Stage III shows fixed deformity with subtalar joint arthritis, and Stage IV involves ankle valgus and deltoid ligament failure. Understanding this progression is crucial as treatment options and prognosis differ significantly between stages.