Background: This two-year randomized clinical trial was performed to examine whether the geometry of the cemented femoral prosthesis affects the pattern of strain-adaptive bone remodeling in the proximal aspect of the femur after primary total hip arthroplasty.
Methods: One hundred and twenty patients were randomized to receive a Charnley (composite-beam), Exeter (double-tapered), or C-Stem (triple-tapered) prosthesis. The change in proximal femoral bone mineral density over two years was measured by dual x-ray absorptiometry (DXA). Bone turnover markers were measured in urine and serum samples collected at the preoperative baseline and during the first postoperative year. N-telopeptide of type-I collagen was measured in urine as a marker of osteoclast activity, and osteocalcin was measured in serum as a marker of osteoblast activity. Clinical outcome was measured with use of the Harris and Oxford hip scores and prosthesis migration was measured with use of digitized radiographs during the first two postoperative years.
Results: The baseline characteristics of the subjects in each group were similar (p > 0.05). Decreases in femoral bone mineral density were observed over the first year for all prosthesis designs, with no further loss during the second year. The decreases were similar in regional distribution and magnitude between the composite-beam and sliding-taper designs (p > 0.05). Bone loss was greatest (14%) in the proximal medial aspect of the femur (Gruen zone 7). Transient increases in both N-telopeptide of type-I collagen and osteocalcin activity also occurred over the first year, and these increases were similar in pattern among the three prosthesis groups (p > 0.05). All prostheses showed migration patterns that were consistent with their design type, and similar improvements in clinical hip scores were observed over the two-year course of the study.
Conclusions: Differences in the mechanism of load transfer between the prosthesis and host bone in composite-beam or sliding-taper cemented femoral prosthesis designs were not a major determinant of proximal femoral bone loss after total hip arthroplasty, and the design that included a third taper exhibited a remodeling profile that was similar to those of the double-tapered design.