Exercise and gait effects on in vivo hip contact pressures.

Virtually all hip rehabilitation programs include exercise for muscle force development. The specific effects of various exercise modes on the hip joint itself are unknown. We will report on the effects of common exercise modalities on in vivo hip pressures. Four years prior to data collection, a pressure-instrumented Austin-Moore-type endoprosthesis was implanted in an otherwise healthy 73-year-old woman with a traumatic right hip fracture. Hip pressures during various experimental maneuvers were recorded periodically over a 5-year period. We compared measurements of peak pressure and rate of pressure rise obtained during gait with those obtained during isokinetic, isometric, and isotonic lower-limb exercises. Maximal exercise generated greater peak pressures than did gait, and tripling the angular velocity during exercise roughly tripled the rate of pressure rise. Torque production and resultant in vivo hip pressures varied directly during all experiments. Peak pressures and rate of pressure rise apparently can be controlled by varying the subject's exertion. The results reported are from a single subject; therefore, little generalizability is possible for these data. We suggest, however, that articular pressures may be important to rehabilitation planning; these data provide a direct insight into this potentially important exercise prescription consideration.