A proposed method for measuring pressures on the human hip joint

Abstract

A method of measuring the spatial and temporal pressure variations on the cartilage surfaces in the human hip joint has been developed. A suitably instrumented standard hip prosthesis replaces the ball portion of the joint and serves as the means by which a number of small pressure transducers are placed in contact with the cartilage surface in the hip socket. This arrangement allows the pressures to be measured as the subject stands, walks or runs.

The instrumented prosthesis must satisfy several requirements. Obviously, the method of measuring pressures must be such that the normal or true pressure distribution is not seriously affected by the measuring technique. The pressuresensing devices must be physiologically acceptable and must have excellent fatigue-life characteristics. Directwire connection from the instrumented prosthesis to external recording equipment is not acceptable due to the danger of infection; so, a radio telemetry link is necessary to monitor pressure-transducer signals.

A pressure-transducer design which satisfies the above requirements is presented, together with a stress analysis of the critical pressure-sensing elements and a description of the proposed telemetry system.