Do gait adaptations during stair climbing result in changes in implant forces in subjects with total hip replacements compared to normal subjects?

Background The study objective was to identify gait abnormalities and their relationships to hip loading during stair climbing after total hip replacement. Hypotheses: (1) total hip replacement subjects would have significantly lower dynamic hip range of motion and peak external moments during stair climbing compared to normal subjects and (2) the peak twisting moment about the long axis of the implant and peak hip forces would be significantly reduced in subjects with total hip replacements compared to normal subjects. Methods Gait parameters during a stair climbing task were measured for 15 total hip replacement subjects and 15 matched normal subjects. Forces were predicted using an analytical model. Findings The peak external adduction moment for the total hip replacement subjects was 25% less than normal (P = 0.001). The external rotation moment was 26% less than normal (P = 0.029) but the extension moment was 77.5% higher in the total hip subjects than in normal subjects (P = 0.004). The peak twisting moment and first peak contact force were 18% and 14% lower in the total hip group compared to normal (P = 0.090 and P = 0.055, respectively). The second peak force was nearly equal (P = 0.424) between the two groups. Interpretation Stair climbing biomechanics differ from normal in subjects with total hip replacements, however these unconscious alterations do not abnormally increase the hip loads during this activity. More work is necessary to determine exactly what constitutes optimal stair climbing biomechanics for patients with total hip replacements.