Comparison of hip force calculations and measurements in the same patient.

Many investigations report hip-contact-force estimates based either on mathematical models or on the output of instrumented implants. Data from instrumented implants have been consistently lower than mathematical predictions. The authors compared mathematical estimates derived from gait laboratory observations made in a patient with an instrumented hip implant. Appropriate modifications to past models resulted in force predictions that were reasonably similar to the output of the instrumented implant. Peak resultant forces were in the range of 2.5-3.5 body weight during level walking at a freely selected speed, while peak out-of-plane forces ranged from 0.6 to 0.9 body weight. Previous parametric hip-force predictions resulting from mathematically modeled surgical alterations may be high insofar as absolute peak values, but trends are likely correct.