The effects of high molecular weight hyaluronan (HA) on cartilage degeneration were investigated in a partial menisectomy model of osteoarthritis (OA) in the rabbit knee. This study compared HA80 (0.8x106 Da, 1%), HA190 (1.9x106 Da, 0.01-1%) and saline. HA (0.1 ml/kg) or saline were injected intra-articularly twice a week immediately after surgery. Degenerative changes in femoral and tibial cartilages were graded histopathologically 2 and 4 weeks after surgery. Two weeks after surgery, HA190, only when used at a 1% concentration, resulted in a dramatic inhibition of cartilage degeneration in both the femoral condyle and the tibial plateau (P < 0.01). Two weeks after surgery, the protection against cartilage degeneration was significantly (P < 0.05) greater with HA190 than with HA80. Four weeks after surgery, only the femoral cartilage degeneration was significantly and similarly inhibited with HA190 (P < 0.01) and HA80 (P < 0.05). Scanning electron micrographs of femoral cartilage showed that cartilage degeneration was less severe with HA190 than with saline. These results might suggest that, in the rabbit model, intra-articular administration of higher molecular weight HA is more effective than lower molecular weight HA in inhibiting cartilage degeneration in early OA.
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