KNEE-JOINT IMMOBILIZATION DECREASES AGGRECAN GENE-EXPRESSION IN THE MENISCUS

Aggrecan is the major proteoglycan of the meniscus, and its primary fu nction is to give the meniscus its viscoelastic compressive properties . The objective of this study was to determine the effect of joint imm obilization on aggrecan gene expression in the meniscus. The right hin dlimbs of six mature beagles were knee cast-immobilized in 90 degrees of flexion and supported by a sling to prevent weightbearing, while th e contralateral limb was left free to bear weight. The animals were sa crificed at 4 weeks, and the anterior and posterior halves of the medi al and lateral menisci were analyzed separately Analysis of aggrecan g ene expression by quantitative polymerase chain reaction showed decrea sed aggrecan gene expression in menisci from immobilized knees (P < 0. 01, two-way analysis of variance). Aggrecan gene expression decreased by a factor of 2 to 5.5 in the different regions examined, Analysis of the composition of the meniscus also showed decreased proteoglycan co ntent and increased water content with immobilization (P < 0.05, two-w ay analysis of variance). These results show that joint immobilization can significantly affect meniscal cellular activity and composition a nd can therefore potentially affect meniscal function.