A case report of index flexor digitorum superficialis and flexor digitorum profundus ruptures caused by a volarly protruding fragment in advanced Kienböck disease: reconstruction with a two-strand palmaris longus tendon graft

Spontaneous flexor tendon rupture is a rare complication of advanced Kienböck disease. A 75-year-old woman presented with progressive loss of active flexion of the left index finger. Radiography, computed tomography, and magnetic resonance imaging demonstrated Lichtman stage IIIC Kienböck disease with a volarly displaced lunate fragment breaching the volar capsule and causing complete rupture of the index flexor digitorum superficialis and flexor digitorum profundus (FDP) tendons, leaving an approximately 5-cm FDP defect. Proximal row carpectomy was performed to remove the fragmented lunate, eliminate the source of chronic attrition, and address wrist pain. The FDP defect was reconstructed using a two-strand looped palmaris longus tendon graft with a modified Pulvertaft weave. At 2 years, satisfactory functional recovery was achieved without re-rupture. Volar lunate fragmentation should be recognized as a cause of flexor tendon rupture, and computed tomography and magnetic resonance imaging are important for accurate diagnosis and surgical planning in such cases.