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Activity Reduces Bone Loss After Total Hip Replacement

In order to stay strong, bones need load and compression spread evenly across the bone. When bone is removed and replaced with a hip prosthesis, the implant changes how the load is placed on the femur (thighbone). This is called stress shielding.

Stress shielding can lead to thinning of the bone and decreased bone mineral density. Changes in the shape and amount of bone from stress shielding can occur. The result may be bone loss around the implant. That could be a problem later on if the total hip replacement has to be revised.

Using 10 cadavers with a total hip replacement (THR) on one side, researchers analyzed the bone after death. They compared changes in bone around the implant on the total hip side to bone on the nonimplanted side. Bone loss and bone density were measured.

They looked at patient activity level and walking ability before death. They also factored in age, implant size, and length of time the patient had the implant. The shape of the bone was measured using computer analysis of the bone cut cross-wise. This is called a cross-sectional analysis.

The authors report that reduced activity and to a lesser extent, patient weight were directly linked to greater bone loss. Age, implant size, and length of time the implant was in place didn't seem to make any difference in bone density.

Patients who limped put a smaller load on the implanted side compared to the nonimplanted hip. Patients who could walk more than six blocks without a limp had less bone loss after THR. This study supports the importance of activity (especially walking) after THR.

References: Teri G. Rosenbaum, PhD Candidate, et al. Ambulatory Activities Maintain Cortical Bone After Total Hip Arthroplasty. In Clinical Orthopaedics and Related Research. September 2006. No. 450. Pp. 129-137.

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