Maintenance of bone mineral density after implantation of a femoral neck hip prosthesis

Background: Stress shielding of the proximal femur has been observed in a number of conventional cementless implants used in total hip arthroplasty. Short femoral-neck implants are claiming less interference with the biomechanics of the proximal femur. The goal of this study was to investigate the changes of bone-mineral density in the proximal femur and the clinical outcome after implantation of a short femoral-neck prosthesis. Methods: We prospectively assessed the clinical outcome and the changes of bone mineral density of the proximal femur up to one year after implantation of a short femoral neck prosthesis in 20 patients with a mean age of 47 years (range 17 to 65). Clinical outcome was assessed using the Harris Hip Score. The WOMAC was used as a patient-relevant outcome-measure. The bone mineral density was determined using dual energy x-ray absorptiometry, performed 10 days, three months and 12 months after surgery. Results: The Harris Hip Score improved from an average preoperative score of 46 to a postoperative score at 12 months of 89 points, the global WOMAC index from 5,3 preoperatively to 0,8 at 12 months postoperatively. In contrast to conventional implants, the DEXA-scans overall revealed a slight increase of bone mineral density in the proximal femur in the 12 months following the implantation. Conclusion: The short femoral neck stem lead to a distinct bone reaction. This was significantly different when compared to the changes in bone mineral density reported after implantation of conventional implants.