PERIPROSTHETIC BMD OF CEMENTLESS THA

Subject: 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 implantat ion of cementless total hip arthroplasty (CLS-stem, Mecron threaded ac etabular cup) by using dual-energy X-ray absorptiometry (DEXA). Materi als and Methods: 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 (Merl e d'Aubigne score > 12). In the cross-sectional study we analysed 23 p atients (13 women, 10 men). Regions of Interest (ROI) were defined acc ording to Gruen. et al. for the periprosthetic femur and to De Lee and Charnley for the periprosthetic acetabulum.Results: BMD significantly decreases in the periprosthetic femur as well as in the periprostheti c acetabulum during the first three months. In men BMD reaches its low est 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 ac etabulum. 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 zo ne II of the acetabulum we observed the highest decrease of mineralisa tion. More than five years after implantation of the prosthesis BMD in the femur showed only Little changes. On the other side BMD around th e threaded acetabular cup significantly decreased to 67,4% in women an d 79,1% in men. Conclusion: The results reflect the different stress o n the periprosthetic bone after implantation of the prosthesis and fit to earlier reported good clinical results of the CLS-stem and to incr eased loosening rate of threaded acetabular cups after five years. Ana lysing changes of mineralisation in cementless total hip arthroplasty DEXA together with the analization scheme according to Gruen at the fe mur and to De Lee and Charnley at the acetabulum is a useful method an d has been reliable in clinical practise.