Lower-limb joint mechanics after total hip arthroplasty during sitting and standing tasks.

While the effect of total hip arthroplasty on the operated limb mechanics is well documented, little is known on its effect on the contralateral limb. The purpose of this study was to measure the joint mechanics of both lower limbs during the tasks of sit-to-stand and stand-to-sit. Twenty total hip arthroplasty patients and 20 control participants performed three trials of each task from which 3D lower-limb joint kinematics and kinetics were obtained. Total hip arthroplasty patients exhibited lower operated-hip joint flexion, extension moments, and power, occurring most frequently near seat-on and seat-off. Despite these reduced kinetic variables in the operated hip, the joints of the non-operated limb generated similar joint kinetics as the matched control participants. These results indicated the patients who underwent total hip arthroplasty could adopt a strategy that allowed them to reduce moments and power generated at the operated lower-limb joints without overcompensating with the non-operated leg. Although such a strategy may be desirable given that higher loads can increase friction and accelerate wear of the prosthesis, reduced loading may be an indication of inadequate muscle strength that needs to be addressed.