Background: The etiology and natural history of Kienböck's disease remain unclear. Traditionally it has been defined as avascular necrosis of the lunate. The authors tried to demonstrate different tissue distribution, the area ratio of necrotic tissue and vessel counts inside the whole Kienböck lunate to reveal a dynamic process of the lunate collapse. Methods: Five lunates from patients with stage III Kienböck's disease and one cadaveric lunate not involved by Kienböck's disease were sampled. They were sectioned, H&E stained, and evaluated. The thickness of trabecular bone and the area of necrotic tissue were measured with Image-Pro Plus. The number of vessels was counted manually. Results: In the normal lunate, the bone trabeculae showed a uniform distribution with fatty marrow filled the interspace between the trabeculae. In the lunates with Kienböck disease, the trabeculae fracture and necrosis located in the central part with massive fibrous granular tissue proliferation. There were also some chondroid metaplasia at the palmar and dorsal ends. The trabeculae of the lunates of the Kienböck's disease [0.188 mm (0.153 mm, 0.236 mm)] was significantly thicker than the normal lunates [0.146 mm (0.124 mm, 0.164 mm)]. The necrosis was localized around the fracture sites instead of the whole lunate. The mean necrosis area only accounts for 16.3% ± 8.9% of the whole section. Such kind of focal necrosis is quite similar to those around the traumatic fracture ends of other bones. Even in stage III Kienböck lunates, the vessels are quite abundant (221 ± 42 in one sagittal section), while the vessels inside the normal lunate were 352 ± 28. Conclusions: There is neither massive nor obvious generalized avascular bone necrosis in our histopathology observations. The focal necrosis and vessel damage were more likely associated with the broken trabeculae inside the lunate. Based on our histopathology observations, we suggested that the progressive process of Kienböck's disease could be described as lunate nonunion advanced collapse instead of avascular necrosis.

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