BONE-DENSITY AND LOCAL GROWTH-FACTORS IN GENERALIZED OSTEOARTHRITIS

Osteoarthritis is usually considered to be a primary disorder of chond rocyte function with secondary changes in bones. However, a defect in the subchondral bone resulting in loss of its shock absorbing capacity could transfer the stress of loading directly to the articular cartil age with secondary changes in the cartilage. Review of histomorphometr ic and bone densitometric studies at sites of osteoarthritis at the hi p or knee revealed that cartilage fibrillation could not be dissociate d from bony changes even in the earliest stages of osteoarthritis and that subchondral trabeculae are thickened and more spaced in osteoarth ritis. Microfractures of subchondral trabecular bone were less frequen tly seen in osteoarthritis compared to controls. Changes of the tidema rk were found to be multiform and metabolically active in the osteoart hritic process. Endochondral ossification depletes the calcified carti lage at the cartilage/bone interface and the tidemark has been thought of as a calcification front advancing in the direction of non-calcifi ed cartilage. Duplication of the tidemark is cited as evidence of this advancement. In the few experimental animal studies of subchondral bo ne in osteoarthritis, thicker trabeculae which were closer together we re found in guinea pigs already when only mild cartilage changes were present. In the dog, with cruciate ligament transection, changes in bo ne were later than in the cartilage, but the changes in bone could sti ll contribute to the progression of osteoarthritis. To study if bone c hanges may precede injury to the cartilage and if metabolic and system ic influences can also alter the subchondral bone, rendering it less a ble to withstand normal mechanical stresses, bone at different sites i n the body has been studied extensively by the authors. Epidemiologica l and case control studies have revealed that osteoarthritis cases hav e more bone at all sites than expected and that bone in cases with gen eralized osteoarthritis shows both quantitative and qualitative differ ences, including increased contents of growth factors and hypermineral ization. These findings suggest that a more generalized bone alteratio n may be the basis of the pathogenesis of osteoarthritis. (C) 1997 Wil ey-Liss, Inc.