[A new classification of semilunar bone necrosis].

The currently accepted classifications of Kienböck's disease by Decoulx and coworkers (1957) as well as Lichtman and coworkers (1977) resp. Lichtman and Degnan (1993) do not take into account early changes in MRI or changes in carpal architecture. A recent publication by Lichtman and Ross (1994) did not solve the problems of precisely describing the disease. This necessitates a new, reliable classification based on the true nature course of the disease. In a prospective study with 49 patients and in a retrospective review of 125 cases of lunate necroses, the regular natural course of the disease was analysed. It begins with normal X-ray appearance but a typical extinguished T1-signal in MRI; a fracture line is part of the later course and not seen in the beginning. Later, collapse of the lunate and the carpus can be observed. A new classification based on the natural course of the disease is proposed. This classification divides the natural course of Kienböck's disease into four stages, subdividing stage I, II and III by A and B. The disease commences with pathology only detectable by MRI (extinguished signal in T1-weighted sequence-stage I A), followed by first changes in the X-ray (condensation or mosaic-like appearance), while the outer form remains preserved (stage I B); the disease proceeds with partial deformation of the lunate with proximal or radial indentation (stage II A), later with a fracture line, while the lunate index of Ståhl remains normal (stage II B); the collapse of the lunate follows, and Ståhl's lunate index becomes pathologic (stage III A); the subsequent collapse of the carpus is characterized by a pathologic Youm-index (stage III B); Kienböck's disease, finally, leads to arthrosis of the wrist.