The development of osteoarthrotic cartilage lesions in the knee joints of male STR/IN mice was studied with respect to their histologic appearance and their various localizations in the joint. Spontaneous articular cartilage degeneration on the medial portion of the tibial plateau was considered to be the initial event. Continued loss of cartilage subsequently led to a pronounced instability of the knee joint, with a varus deformity. This was followed by medial patellar luxation with corresponding osteoarthrotic lesions at the facies patellaris femoris. The most marked osteoarthrotic cartilage degeneration developed on the medial tibial condyle and at the facies patellaris femoris of the femoropatellar joint. Histologic examination of the osteoarthrotic defects in these two regions revealed distinct morphologic differences with respect to formation of chondrocyte clusters, tendency to regeneration, and proliferation reactions. Lectin binding experiments in normal articular cartilage revealed regional differences regarding the presence or absence of keratan sulfate in the extracellular matrix. The lack of keratan sulfate in tibial cartilage might reflect its tendency to degenerate spontaneously. It is therefore suggested that male STR/IN mice are particularly useful for studying two different types of osteoarthrosis, one due to a biomechanically induced instability (patellar luxation) and one due to biochemical changes (absence of keratan sulfate) of still unknown pathogenesis.

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