Do subchondral bone changes exacerbate or precede articular cartilage destruction in osteoarthritis of the elderly?

Research into the aetiology of osteoarthritis has for several decades been concentrated on the destruction of the articular cartilage, the initiating events being believed to be changes in the proteoglycans and subsequently in the supporting collagenous framework, whereafter the disease is irreversible. Recent evidence has supported an old contention that the underlying bone may be involved, namely, increased technetium scintigraphy correlated with increased severity of the osteoarthritis as demonstrated by joint narrowing, and a demonstration of increased metabolism of cancellous bone collagen compared to age-matched controls. These studies have not been able to answer the question of the primary initiating event: does increased bone metabolism initiate cartilage destruction or vice versa? However. recent detailed studies on animal models, particularly the macaque, have demonstrated that in this case thickening of the subchondral bone precedes fibrillation of the cartilage, which is possibly due to increased resistance of the bone to compression. Further, MRI studies on the guinea pig suggest that the initial site of activity is at the ligament bone insertion site, prior to endochondral bone sclerosis. We propose that the biomechanics of the joint are perturbed by the loss of tension from the ligament following trauma, leading to remodelling of the subchondral bone. Certainly in humans damage to the cruciate ligament often results in osteoarthritis. It may be that subclinical damage also ultimately results in osteoarthritis. Although the results from animal models will need to be treated with caution, the concept that bone ligament changes precede articular cartilage destruction should lead to a redirection of research, and perhaps therapy, for this important and cruelly disabling disease.