Objective: To describe the changes in subchondral bone that occur with the onset and progression of osteoarthritis (OA) from macroradiographic assessment of patient's hand and knee joints.
Design: The high magnification and spatial resolution of macroradiography permits detailed anatomical changes to be detected in OA joints. Data on the subchondral cortical and cancellous bone, recorded from both cross-sectional and longitudinal studies of hand and knee OA, are described and discussed with reference to recent findings on the altered biomechanical properties of OA bone.
Results: In OA joints, both subchondral cortical plate and subjacent horizontal trabeculae increase in thickness early, prior to joint space narrowing (JSN). With progression, cortical plate sclerosis increased in 60% of OA hands and did not change in knee OA until JSN <1.5mm in the medial diseased compartment. In knee OA, trabeculae, at sites of tibial subchondral sclerosis, increased in number and extent, changes that overlay a subarticular region that was osteoporotic. With cartilage loss, the articular surfaces in some knees appeared corrugated, and later, with bone-on-bone, the surfaces became flattened and deformed.
Conclusions: The weaker than normal bone within thickened subchondral cortical plate and trabeculae of OA joints leads, in advanced OA, to deformation of the articular surfaces and absorption of local stresses producing an effect similar to stress-shielding. This effect, it is suggested, results in the subarticular osteoporosis.