The effects of hyaluronan on the meniscus and on the articular cartilage after partial meniscectomy.

The effect of hyaluronan (molecular weight = 8 x 10(5)) on the meniscus and on the articular cartilage was assessed after partial meniscectomy in a rabbit model. On gross examination, remodeled meniscus appeared as newly synthesized translucent tissue, and was seen in both vehicle- and hyaluronan-treated menisci. Histologically, safranin O staining revealed the strong presence of glycosaminoglycans in the newly remodeled tissue, and polarized light demonstrated the absence of mature collagen architecture. Hydration of the hyaluronan-treated menisci was significantly less than that of the vehicle-treated menisci, and the reducible collagen cross-link dihydroxylysinonorleucine was significantly increased in the hyaluronan-treated menisci compared with the vehicle-treated menisci, indicative of a greater degree of collagen remodeling. In situ hybridization of vehicle- and hyaluronan-treated menisci revealed a high level of type I procollagen mRNA expression and minor expressions of types II and III mRNA. Expression of the type I collagen gene appeared to be more pronounced in the hyaluronan-treated menisci than in the vehicle-treated menisci. The tibial plateaus revealed mild cartilage fibrillation after partial meniscectomy. A statistically significant difference between vehicle- and hyaluronan-treated cartilage was not demonstrated in the present study because of the slow development (i.e., 12 weeks) of osteoarthritis after partial meniscectomy in the rabbit model. These results suggest that in the rabbit model, hyaluronan enhances collagen remodeling and inhibits meniscal swelling after partial meniscectomy in the avascular region.