[Changes in bone density of the femur after cement-free implantation of a modular hip prosthesis with a long shaft]. / Veränderung der Knochenmasse des Femurs nach zementfreier Implantation einer modularen Hüftprothese (MHP) mit langem Schaft.

Until now, no reports exist on the existence of femoral bone loss after hip arthroplasty using long-stem cementless prostheses in elderly patients. In a prospective evaluation the amount of bone loss (stress-shielding) after implantation of a long stem hip prosthesis in patients with femoral neck fractures (group A) or pertrochanteric femoral fractures (group B) was examined. Eleven patients (five from group A and six from group B) were treated with a long-stem modular hip prosthesis (MHP). Change of bone mass was evaluated using quantitative computed tomographie (QCT) immediately following and at six months (group A and B) and twelve months (group A) after implantation of the prosthesis. Clinical results, expressed with the modified Harris Hip Score, and relative changes of bone mass were compared with mean periprosthetic bone mass of the femur after operation. After implantation of the MHP, the maximum decrease of mean femoral bone mass was 19.1% at six months and 20.2% at twelve months for group A and 29.5% at six months for group B. Bone loss in the proximal periprosthetic area was higher than in the distal part. There was no correlation between baseline values of bone mass and the amount of stress-shielding or clinical outcome.