Subcutaneous extensor tendon rupture caused by Kienböck disease complicated by carpal tunnel syndrome: A case report

Subcutaneous extensor tendon rupture caused by Kienböck disease is rare. Only 22 cases have been reported in the English literature since 1986.

A 74-year-old male experienced numbness of his right hand for several years and was unable to extend his right middle and ring finger 2 months before consultation.

Physical examination revealed no pain in his right wrist, but was unable to extend the middle and ring fingers. He also had numbness of the thumb, index, middle, and radial side of the ring finger. Plain radiography and computed tomography revealed osteoarthritis of the wrist and segmental lunate bone. Ultrasonography revealed disruption of the extensor tendon, indicating that the lunate bone volar fragment did not interfere with the flexor tendons and median nerve. Magnetic resonance imaging suggested extensor tendon rupture. Nerve conduction studies showed delayed distal motor latencies of the abductor pollicis brevis muscle. We diagnosed subcutaneous rupture of the extensor tendons of the middle and ring fingers caused by stage Ⅳ Kienböck disease complicated by carpal tunnel syndrome.

A 2-portal endoscopic carpal tunnel release was performed under general anesthesia. A dorsal curved incision was made. The dorsal fragment of the lunate punctured the capsule, and the extensor digitorum communis (EDC) tendon of the middle, ring, and little fingers, and the extensor indicis proprius tendons were ruptured. The dorsal fragment of the lunate bone was removed and the EDC tendon of the middle finger was transferred to that of the index finger. The combined EDC tendons of the ring and little fingers were transferred to the extensor digitorum minimi tendon.

The numbness and extension restriction of the middle and ring fingers had improved at 2 years postoperatively. Dorsal and volar flexion were up to 60°.

Dorsal lunate bone fragments associated with advanced Kienböck disease can cause extensor tendon rupture. When ultrasonography confirms that the volar fragment of the lunate bone does not impinge upon the median nerve or flexor tendons, surgical intervention on the volar fragment may be unnecessary. Computed tomography, magnetic resonance imaging, and ultrasonography are valuable for accurate assessment and preoperative planning.