Hydraulic Joint Function and Osteoarthritis.

» This review of bone perfusion work introduces a new field of subchondral physiology.» Intraosseous pressure (IOP) measured through an intraosseous needle reflects conditions only at the needle tip rather than being a constant for the whole bone.» Measurements of IOP in vitro and in vivo, with and without proximal vascular occlusion, show that at rest, bone is perfused at normal physiological pressures.» A subtraction perfusion range or bandwidth at the needle tip offers a better measure of bone health than a single IOP.» With ordinary loads, very great subchondral pressures are generated.» Subchondral tissues are relatively delicate but are microflexible with bone fat being essentially liquid at body temperature.» Collectively, the subchondral tissues transmit load mainly through hydraulic pressure to the trabeculae and cortical shaft.» White vascular marks on normal magnetic resonance imaging scans are present but are lost in early osteoarthritis.» Histological studies confirm the presence of those vascular marks and also choke valves capable of supporting hydraulic pressure load transmission.» Osteoarthritis seems to be at least partly a vasculomechanical disease.» Understanding subchondral physiology will be key to better classification, control, prognosis, and treatment of osteoarthritis.