Effect of femoral component offset on polyethylene wear in total hip arthroplasty

Seventeen staged, bilateral total hip arthroplasties performed in 17 patien ts were reviewed to compare side-to-side polyethylene wear. Implants used o n both sides were similar except for implant offset: one hip in each patien t was replaced using a femoral component having a standard implant offset, whereas the other side had a lateral offset implant. The mean followup was 5.70 years (range, 2-10.2 years) on the side with a standard femoral implan t and 5.67 years (range, 2-9.7 years) on the side with a lateralized femora l component. The only statistically different parameter between the sides w as the femoral component offset. All other parameters affecting polyethylen e wear, such as period of followup, head size, head type, cup size, cup inc lination, medialization of cup, and patient-related factors were similar on both sides, On the side with a standard femoral component, the mean actual prosthetic offset (determined by manufacturer's specifications) was 35.2 m m and the radiologic offset was 31.5 mm, On the side with a lateralized fem oral component, the actual prosthetic offset was 42.5 mm and the radiologic offset was 40.1 mm, The difference in offsets between the sides was statis tically significant. The mean preoperative offset of the femur was 38.8 mm. Regression analysis revealed that only femoral component offset and cup si ze correlated significantly with linear wear rate. On the side with a stand ard femoral component, the linear wear rate was 0.21 mm per year, whereas o n the side with a lateralized femoral component, the linear wear rate was 0 .10 mm per year. The differences in the linear wear rates were significant. Lateralization of the femoral component in this series more closely restor ed preoperative hip biomechanics and significantly decreased polyethylene w ear.