Background: Total hip arthroplasty changes
the levels of stress within the proximal part of the femur, and
the femur remodels adjacent to the prosthesis. The stem size and
the initial bone-mineral density around the distal portion of the
stem affect postoperative bone-remodeling after the insertion of
a fully porous-coated metal-cancellous prosthesis. The purpose of
this study 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 patients was performed. Thirty-one hips in twenty-seven
patients with a fully porous-coated stem (Group A) and thirty hips
in twenty-seven patients with a proximally porous-coated stem (Group
B) were followed for twenty-four to thirty months. Periprosthetic
bone-mineral density was measured with dual-energy x-ray absorptiometry at
specific intervals after the operation.
Results: In both groups, the greatest loss of
bone-mineral density, compared with the initial (three-week) value,
was approximately 20 percent in zone 7 at twelve to eighteen months.
In other zones, bone-remodeling appeared to cease by twelve months. At
the last follow-up evaluation, the loss of bone-mineral density
in the distal and middle regions in Group A was significantly greater
than that in Group B (p < 0.01 for zone 3 and p < 0.05 for
zone 6). In contrast, with the numbers available, there were no
significant differences 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 distal periprosthetic region rather than in
the proximal region. The results in the present report are specific
to the particular implants that were studied.