Alteration of collagen network and negative charge of articular cartilage surface in the early stage of experimental osteoarthritis

Forty-eight mature male Japanese white rabbits were subjected to unilateral resection of a segment of the gluteal muscles at the sacral origin and a s ection of infrapatellar ligament. Animals were killed at 1, 2, 4, and 8 wee ks postoperatively, and the articular cartilage of the femoral heads was ev aluated. The collagen fibrillar network of the articular surface was observ ed by scanning electron microscopy (SEM) using microdissection by ultrasoni cation. Cationized ferritin (CF) was used for the labeling of negative char ges on the articular surfaces and the thickness of CF layers was observed u nder the transmission electron microscope. Metachromasia of the matrix decr eased remarkably at 4 weeks postoperatively, and fibrillation of the articu lar surface was evident at 8 weeks postoperatively. Derangement and rupture of the collagen network developed as early as 1 week after surgery. The th ickness of the CF layer significantly decreased at 4 weeks postoperatively. This study confirms that alterations of the articular surface, such as der angement of the collagen network and loss of the negative charge, are some of the earliest changes in osteoarthritis. In addition, application of ultr asonication with proper frequencies to the articular cartilage effects an o ptimal removal of mucus, with the consequent exposure of a well-preserved a rticular surface for SEM study.