Lunate fractures generally occur in association with other carpal injuries. It is rare to have an isolated lunate injury. Like many other carpal injuries, it usually is the result of a fall on the outstretched hand. There will be localized tenderness in the middle of the wrist. The lunate is present in the shallow indentation on the mid-dorsum of the wrist. If the wrist is flexed the lunate is easily palpable as it rises out of the floor of this indentation. Axial pressure applied along the third metacarpal ray may also elicit pain in this same area and is suggestive of injury. Like the scaphoid, the lunate's blood supply enters through the distal end. A fracture risks producing avascular necrosis to the proximal portion. Because the lunate is nestled in the middle of the wrist, overlap with other carpal bones may make it difficult to identify an injury on a plain radiograph. Clinical suspicion should dictate the acute treatment. A thumb spica splint should be applied until further evaluation by the orthopedist. MRI and CT to identify occult fractures have replaced tomography and bone scans. The major complication is avascular necrosis (Kienbock's disease) that can lead to lunate collapse, osteoarthritis, chronic pain and decreased grip strength. Repetitive trauma to the lunate can also produce microfractures of the bone and subsequent osteonecrosis (see Fig.,,,262-10). Individuals with ulnar negative variance are at increased risk of developing Kienbock's disease, because a shorter ulna provides less support to the lunate.
FIG. 262-10. Kienbock's disease, osteonecrosis, and collapse of the lunate. (With permission from Chin HW, Visotsky J: Wrist fractures. Em Med Clin North Am 11:3, 1993.)
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