Experimental temperature rise in human hip joint in vitro in simulated walking

Although reported frictional coefficients in synovial joints are very low, a computer model of the human hip joint in simulated walking predicted a temperature rise of several degrees Celsius. To confirm this prediction, physical experiments were conducted in vitro on intact human hip joints dynamically loaded and articulated as in walking. Thermisters were placed in subchondral bone in both the acetabulum and femoral head, just below the cartilage layers. The surrounding saline bath was maintained at 37 degrees C. Measured temperatures as high as 2.5 degrees C above the 37 degrees C were recorded in the subchondral bone. Loading that simulated the stance/swing phases of gait but without articulation produced no significant increase in temperature; thus fluid flow per se is not significantly energy dissipative; the prime source is friction at the articulating surfaces.