Case Report: A tibial spur causing posterior tibial tendon dysfunction - intraoperative dynamic evidence.

Posterior tibial tendon dysfunction (PTTD) is a progressive and disabling condition that is frequently misdiagnosed, particularly in the context of ankle sprain. Distal tibial spurs have been identified as secondary imaging findings in PTTD, with prior studies reporting a significant statistical association between spur presence and high-grade posterior tibial tendon (PTT) tears. However, whether a tibial spur can directly cause PTT injury through mechanical impingement remains unestablished, with no direct evidence or case reports to date. We report the case of a 33-year-old male who presented with persistent medial ankle pain following recurrent ankle sprains, having undergone a prior lateral ligament repair at an outside institution without symptomatic improvement. Physical examination revealed pronounced tenderness along the PTT sheath with a palpable nodular induration, and the patient was unable to complete the single-limb heel rise test. A diagnostic local anesthetic injection into the PTT sheath resulted in approximately 70%-80% pain relief. Computed tomography identified a posteromedial tibial bony prominence in close anatomical proximity to the PTT. Intraoperative passive plantar flexion and dorsiflexion testing under direct visualization demonstrated repetitive frictional abrasion of the PTT by the tibial spur, providing, to our knowledge, the first reported intraoperative dynamic evidence of mechanical PTT impingement by a tibial spur. A combined surgical procedure comprising spur excision, primary PTT repair, and tarsal tunnel reconstruction was performed. At one-year follow-up, the patient demonstrated substantial clinical improvement, with the Visual Analog Scale pain score decreasing from 7 to 1, the American Orthopaedic Foot and Ankle Society ankle-hindfoot score improving from 32 to 80, and successful completion of the single-limb heel rise test with restoration of hindfoot inversion. This case highlights a rare but clinically significant cause of PTT injury and suggests that bony impingement by a tibial spur should be considered in the differential diagnosis of persistent medial ankle pain following ankle sprain. Computed tomography is recommended as a complementary imaging modality to magnetic resonance imaging when bony impingement is suspected.