[Periprosthetic mineral density in cement-free hip replacement arthroplasty]

We analysed the periprosthetic bone mineral density (BMD) in a prospective longitudinal study over two years after operation and in a separate cross-sectional study more than five years after implantation of cementless total hip arthroplasty (CLS-stem, Mecron threaded acetabular cup) by using dual-energy X-ray absorptiometry (DEXA).

In n = 53 patients (29 women, 24 men) we analysed the periprosthetic BMD prospectively in certain periods. All patients had an uncomplicated postoperative course and good clinical outcome (Merle d'Aubigne score > 12). In the cross-sectional study we analysed 23 patients (13 women, 10 men). Regions of Interest (ROI) were defined according to Gruen et al. for the periprosthetic femur and to De Lee and Charnley for the periprosthetic acetabulum.

BMD significantly decreases in the periprosthetic femur as well as in the periprosthetic acetabulum during the first three months. In men BMD reaches its lowest values between six months (femur) and one year (acetabulum) after operation and then increases to 96.2% at the femur and 93.8% at the acetabulum. In women BMD decreases during the entire follow-up to 89.4% at the periprosthetic femur and 80.0% at the periprosthetic acetabulum. In the proximal zones 1 and 7 of the femur and the cranial-medial zone II of the acetabulum we observed the highest decrease of mineralisation. More than five years after implantation of the prosthesis BMD in the femur showed only little changes. On the other side BMD around the threaded acetabular cup significantly decreased to 67.4% in women and 79.1% in men.

The results reflect the different stress on the periprosthetic bone after implantation of the prosthesis and fit to earlier reported good clinical results of the CLS-stem and to increased loosening rate of threaded acetabular cups after five years. Analysing changes of mineralisation in cementless total hip arthroplasty DEXA together with the analization scheme according to Gruen at the femur and to De Lee and Charnley at the acetabulum is a useful method and has been reliable in clinical practise.