Effects of valgus tibial angulation on cartilage degeneration in the rabbit knee.

Thirteen adult female rabbits underwent unilateral osteotomy of the proximal tibia. In nine animals, 30 degrees of valgus angulation was created; in four animals, osteotomy without angulation was performed. After a 12-week survival period, the knee joints were processed for histology by staining with hematoxylin and eosin and safranin O. Additionally, the chondroitin sulphate epitopes 3-B-3(-) and 7-D-4 were evaluated immunohistochemically as markers of osteoarthritis. Changes of the articular surface of the tibia were visualized by scanning electron microscopy. Light microscopic evaluation by the Mankin et al. scoring system revealed mild or moderate damage of the cartilage in the lateral compartment of angulated extremities when compared with the control side. Immunohistology with the monoclonal 3-B-3 and 7-D-4 antibodies showed no increased expression of these epitopes in the lateral compartments of the knee. Scanning electron microscopic evaluation of the tibial surfaces revealed slight surface damage localized to the central, weight-bearing portion of the lateral tibial plateau of angulated extremities. Angulation of 30 degrees led to only mild degenerative changes of the cartilage. These results indicate that, in the short term, cartilage has considerable capacity to withstand the effects caused by severe angulation of the limb.