IS STAIRCASE WALKING A RISK FOR THE FIXATION OF HIP IMPLANTS

Considerable forces and moments act at hip prostheses during most kinds of physical activities. High torque around the stem axis may contribute to implant loosening. With instrumented hip prostheses the joint force and its direction, the bending moment in the frontal plane and the torque were measured in two patients during upstairs, downstairs and level walking. The data give information on whether or not stairclimbing causes a more severe loading situation for the implants than walking. While going upstairs at normal speed the joint force is 10% higher than during walking at 3 km h(-1). Downstairs it increases by 20%. The bending moments change by nearly the same amounts. Upstairs the torsional moment is about twice as high as during slow walking. But walking at 5 km h(-1) or slow jogging causes forces and moments of similar magnitudes. Even higher loads were observed when the patients stumbled without falling. Although torque during staircase walking is high, extreme values exclusively during stairclimbing are not confirmed by our data. The torsional moments now observed in vivo are close to or even exceed the experimentally determined limits of the torsional strength of implant fixations, found in the literature. Obviously, torsional moments play an important role for the potential loosening of hip prostheses.