The vascularity of the wrist. Identification of arterial patterns at risk.

The intraosseous and extraosseous vascularity of carpal bones was studied in 75 cadaver limbs. Vascular patterns were correlated with the clinical incidence of avascular necrosis, and at-risk patterns of vascularity were identified. The carpal bones were found to fall into three groups. Group 1, which consisted of the scaphoid, the capitate, and eight percent of the lunates, had either vessels entering only one surface or large areas of bone that were dependent on a single vessel. This group was the most vulnerable to posttraumatic avascular necrosis. The bones of Group 2, the hamate and the trapezoid, were characterized by the absence of internal anastomoses. Although these bones are theoretically at risk, they do not undergo avascular necrosis. Group 3 bones, which included the trapezium, the triquetrum, the pisiform, and 92% of the lunates, had rich internal anastomoses and were at least risk of undergoing avascular necrosis. Examination of the arterial anatomy of bones that undergo avascular necrosis in other regions of the body led to a classification based on the types of vascular interruptions that place particular bones at risk. In some, i.e., the scaphoid and the capitate, a pure intraosseous disruption resulted in avascular necrosis; in others, i.e., the femoral head and a small percentage of lunates, an extraosseous disruption was sufficient to produce avascular necrosis. A third class, which included the talus and the majority of lunates, had an adequate intraosseous blood supply and good extraosseous vascularity. This pattern required severe extraosseous or a combination of intraosseous and extraosseous injury to lead to avascular necrosis.