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Factors Affecting Bone Remodeling after Cementless THA:
A Report of Two Cases

CA Engh Jr, Sychterz CJ, and Engh CA Sr.

This postmortem study of two patients with cementless total hip arthroplasties illustrates the effect of stem stiffness on bone remodeling.

Methods: We performed a postmortem comparison on femurs from two patients who had cementless total hip arthroplasties with femoral prostheses of different stiffness implanted in the right and left hips.

Results: All four femoral arthroplasties were bone ingrown distally. The femurs with the stiffer prosthesis had a 65-79% greater loss of proximal bone mineral density than the femurs with the more flexible prosthesis. The femurs with the stiffer prosthesis also had decreases in cortical area and cortical bone density. However, the second case had a dramatically greater loss of bone from side to side that could not be attributed to either bone quality or stem stiffness. This patient had clinical diagnoses that affected the bone remodeling pattern more than the differences in stem stiffness.

Finally, although the femurs with the stiffer prostheses had greater bone loss, the more flexible prostheses demonstrated cantilever bending and failure of proximal osseointegration. We are not aware of another bilateral human postmortem analysis that illustrates the effect of stem stiffness on bone remodeling.

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