ARTHRITIS NOT IMMOBILIZATION CAUSES BONE LOSS IN THE CARRAGEENAN INJECTION MODEL OF INFLAMMATORY ARTHRITIS

One suggested cause of the high turnover osteopenia of experimental in flammatory arthritis is disuse of affected joints. To compare the infl uence of immobilization or disuse, or both, with that of inflammatory arthritis on bone turnover, rabbits were placed into four groups. In g roup 1, arthritis was induced in the right knee by seven intra-articul ar injections of 1% carrageenan, over 49 days; in group 2, a plaster c ast was applied to immobilize the right hindlimb in flexion; in group 3, arthritis was induced and the hindlimb was immobilized; and in grou p 4, nothing was done (control). The fluorescent label calcein was adm inistered in drinking water (0.05%) ad libitum to all groups on days 2 2-36. On day 49, specimens were prepared for analysis of bone volume a nd new bone volume at a near site (right femur) and at remote sites (c ontralateral femur and ipsilateral humerus). The data were analysed by multiple regression and Bonferroni tests. In group 1, new bone volume was three times higher than in group 2 or 4 (p < 0.05 for each compar ison); this indicated increased bone remodeling in the right femur. Th is contrasted with group 2, in which neither index of bone remodeling was changed. The combination of immobilization with arthritis resulted in more intense osseous effects of inflammatory arthritis, with a one -quarter decrease in bone volume (group 3, 30.99 +/- 2.50; group 4, 42 .07 +/- 2.38, p < 0.05), as well as a 4-fold increase in new bone volu me (p < 0.001) compared with group 1. A possible systemic effect in th is model of arthritis was evidenced by increased new bone volume in th e contralateral femur in the group that had arthritis and immobilizati on (4.66 +/- 0.57, p < 0.05).