Dear Sir,A 54-year-old woman was referred with inability to flex her dominant right little finger (Fig 1). Four weeks earlier, she had felt a snap in the hand when she squeezed a towel and suddenly became unable to flex the proximal interphalangeal joint of the finger. She had been unable to flex the distal interphalangeal joint in the same finger since birth. She also had 20deg flexion contractures of the proximal interphalangeal joints of both little fingers. She had no history of previous hand injury, tenosynovitis or inflammatory arthritis. X-ray and computed tomography showed no bony abnormalities. MRI showed that the flexor digitorum profundus (FDP) tendon was completely absent and the flexor digitorum superficialis (FDS) tendon was not in continuity in the distal palm (Fig 2). The cross-section of the FDS tendon at the base of proximal phalanx was less than 50 of that in the contralateral little finger on the MRI. Spontaneous rupture of the FDS tendon and aplasia of the FDP tendon were diagnosed.
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