Dorsal dislocations of the lunate are exceptionally rare injuries.1 A 51-year-old, right-hand-dominant man was involved in a high-speed rollover truck collision as an unrestrained passenger. He presented with a solitary complaint of severe pain of his right wrist.
His medical history included hypertension and bilateral hip replacements. He described previously untreated chronic wrist pain.
On examination, his right hand and wrist were swollen and tender, with no neurovascular injury. Radiographs demonstrated an intraarticular fracture at the base of the proximal phalanx of the fifth finger, a comminuted intraarticular fracture of the radial styloid, and a dorsal dislocation of the lunate with coexistent arthritis in the carpometacarpal and scaphotrapeziotrapezoid joints (Fig. 1).
On open reduction, the lunate was found below the skin, outside the extensor retinaculum, and attached to a piece of capsule, devoid of vascular attachments. The extensor tendons were intact. There was a complete tear of the scapholunate and lunotriquetral ligaments. Almost half of the radial articular surface was comminuted.
After reduction and fixation, an attempt was made to reconstruct the dorsal capsule and dorsal and volar radiocarpal ligaments. The wrist was immobilized for 8 weeks. Radiographs at 6 weeks demonstrated reasonable carpal alignment; the lunate appeared sclerotic and avascular (Fig. 2).
The patient returned to his previous occupation as a truck driver. One-year review revealed no functional deficit and mild wrist pain similar to his preinjury pain.
Examination found the following: 62 percent of the uninjured flexion/extension arc (39/45 and 74/61 degrees), ulnar deviation of 20 degrees/26 degrees on the injured side, and radial deviation of 10 degrees/15 degrees. Grip strength was 68 percent (53/78 lb), tripod pinch was 60 percent (9.7/16.3 lb), and lateral pinch was 110 percent (16.6/15.6 lb) that of the uninjured side. Radiographs demonstrated arthritis and generalized osteoporosis but no evidence of avascular necrosis of the lunate. Magnetic resonance imaging was suggestive of partial lunate avascular necrosis.
Lunate dislocation is considered the final stage of a perilunate dislocation.2 Typically, it dislocates volarly into the carpal tunnel. Mayfield surmised that wrist injuries are influenced by the direction and magnitude of the load and force together with properties of the involved bones and ligaments.3 We think this lunate dislocated dorsally because of the force characteristics (volar to dorsal) and because of the preexisting arthritis of the scaphotrapeziotrapezoid and radiocarpal joints. Because the areas of least resistance were the attenuated scapholunate ligament and space of Poirier with a relatively stable scaphoid, the lunate was dislocated. Attenuation of the perilunate ligaments limited the force required for dislocation.
An acute proximal row carpectomy would have addressed the patient's preexisting instability and arthritis. Van Kooten et al. mention an intact radioscaphocapitate ligament as a prerequisite for successful acute proximal row carpectomy, which may not have existed.4
Transient findings of increased density of the lunate or signs of avascular necrosis in the lunate following perilunate dislocation have been described.5 In this case, the completely avascular lunate may have recovered partial vascularity. This, together with the good clinical result, may support attempting reduction in the acute setting over primary proximal row carpectomy.
Timothy Neavin, M.D.
W. P. Andrew Lee, M.D.
Ronit Wollstein, M.D.
Department of Surgery
Division of Plastic and Reconstructive Surgery
University of Pittsburgh Medical Center
1. Bilos ZJ, Hui PW. Dorsal dislocation of the lunate with carpal collapse: Report of two cases. J Bone Joint Surg (Am.)
2. Mayfield JK, Johnson RP, Kilcoyne RK. Carpal dislocations: Pathomechanics and progressive perilunar instability. J Hand Surg (Am.)
3. Mayfield JK. Mechanism of carpal injuries. Clin Orthop Relat Res.
4. van Kooten EO, Coster E, Segers MJ, Ritt MJ. Early proximal row carpectomy after severe carpal trauma. Injury
5. White RE Jr, Omer GE Jr. Transient vascular compromise of the lunate after fracture-dislocation or dislocation of the carpus. J Hand Surg (Am.)
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