Bone pain and pressure in osteoarthritic joints.

Intraosseous hypertension has been associated with a deep aching bone pain, particularly at rest, in subsets of patients with osteoarthritis of the hip and knee. The pathophysiology of this problem remains uncertain, but intraosseous phlebography implicates outflow impairment at relatively distal venous sites. Although the issue has been controversial, intraosseous pressures rise normally, and painlessly, when epiphyseal bone is loaded and these pulses may be mechanically meaningful in the distribution and transmission of impact energy. Increased outflow resistance may amplify the episodic pressure response with subsequent intravasation of epiphyseal fat leading to 'marrow oedema' and altered mechanics. The relationship between persisting pain and pressure is an old but convincing association. Its precise mechanism in osteoarthritis remains in need of an adequate explanation.