Evaluation of periprosthetic bone-remodeling after cementless total hip arthroplasty - The influence of the extent of porous coating

Background: Total hip arthroplasty changes the levels of stress within the proximal part of the femur, and the femur remodels adjacent to the prosthes is. The stem size and the initial bone-mineral density around the distal po rtion of the stem affect postoperative bone-remodeling after the insertion of a fully porous-coated metal-cancellous prosthesis. The purpose of this s tudy was to evaluate the influence of the extent of porous coating of this prosthesis on femoral bone-remodeling. Methods: A longitudinal examination of sixty-one hips in-fifty-four patient s was performed. Thirty-one hips in twenty-seven patients with a fully poro us-coated stem (Group A) and thirty hips in twenty-seven patients,vith a pr oximally porous-coated stem (Group B) were followed for twenty-four to thir ty months. Periprosthetic bone-mineral density was measured,vith dual-energ y x-ray absorptiometry at specific intervals after the operation. Results: In both groups, the greatest loss of bone-mineral density, compare d with the initial (three-week) vialue, was approximately 20 percent in zon e 7 at twelve to eighteen months. In other zones, bone-remodeling appeared to cease by twelve months. At the last followup evaluation, the loss of bon e-mineral density in the distal and middle regions in Group A was significa ntly greater than that in Group B (p < 0.01 for zone 3 and p < 0.05 for zon e 6). In contrast, with the numbers available, there were no significant di fferences in loss of bone-mineral density in the proximal regions (zones 1 and 7) between the two groups at any follow-up period. Conclusions: The extent of porous coating affects bone-remodeling in the di stal periprosthetic region rather than in the proximal region. The results in the present report are specific to the particular implants that mere stu died.