Subchondral physiology and vasculo-mechanical factors in load transmission and osteoarthritis

There is an inverse relationship between the number of MRI marks and Kellgren-Lawrence grade of osteoarthritis, both medially and laterally.²⁸ While cause and effect remain to be separated, the relationship between vascular disease, osteoarthritis (OA), and osteoporosis is of orthopaedic interest.^30–32 Vasculomechanical mechanisms may explain other orthopaedic phenomena, for example the generally mutually exclusive nature of osteoporosis and OA. Several studies have suggested a link between subchondral bone health and OA.^33–35 However, it may be that the softer subchondral bone of the osteoporotic patient flexes proportionately more and is thereby better perfused than the harder sclerotic bone found in OA.

In conclusion, we present a novel understanding of joint physiology and subchondral bone circulation. At rest, subchondral cancellous bone behaves as a perfused tissue with IOP being mainly due to arterial supply rather than venous back pressure or tissue turgor. A single measure of IOP is variable and meaningless, reflecting only conditions at the needle tip. The difference in IOP with proximal venous and arterial occlusion possibly offers a better method for assessing perfusion at the needle tip. A substantial proportion of the load applied to a joint is transmitted through hydraulic pressure to the trabeculae. Subchondral tissues and vascular structures are designed to support hydraulic forces. Vessels are lost in early OA, suggesting that vasculo-mechanical physiology in the subchondral region may play a role in the development of OA. Our proposition opens the door to novel means of research, diagnosis, surveillance, and prognosis and in due course potentially better treatments for OA.