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In a prospective longitudinal study over 2 years and a separate cross-sectional study more than 5 years after operation, we analyzed periprosthetic bone mineral density (BMD) after cementless total hip arthroplasty (THA) (press-fit cementless Spotorno stem, Mecron threaded acetabular cup) by dual-energy X-ray absorptiometry (DEXA). BMD was analyzed in a longitudinal prospective study (n = 53 patients: 29 women, 24 men) and in a separate cross-sectional study (n = 23 patients: 13 women, 10 men) with good clinical outcome (Merle d' Aubigne score > 12). Regions of interest were defined according to Gruen (ROI 1-7) and as netto average ROI (NETAVG I) for the periprosthetic femur, and according to De Lee and Charnley (ROI I-III) and as NETAVG II for the periprosthetic acetabulum. BMD during follow-up was compared with immediate postoperative values of the affected limb. Mean precision error (CV%) was 2.6 +/- 0.5% for ROI 1-7 and 1.3 +/- 0.9% for ROI I-III. BMD significantly decreased in the periprosthetic femur and acetabulum during the first 3 months after operation. At the femur, BMD (NETAVG I) for women and men, respectively, was 92.4% and 87.5% at 6 months, then 89.4% and 96.2% at 2 years. ROIs around the proximal stem showed the lowest absolute values and decreased most during follow-up (to 79.9% ROI 1 and 68.2% ROI 7, respectively). Mineralization around the cup (NETAVG II), respectively, amounted to 81.1%, 82.6% at 6 months, then 80.1% and 93.8% at 2 years. The medially placed ROI II demineralized most (respectively, 72.1% and 76.7%). More than 5 years after THA, BMD in the femur showed little change, but decreased significantly to 76.4% and 79.1%, respectively, around the cup (NETAVG II). DEXA is a useful method for analyzing changes of mineralization around cup and stem of cementless THA. The results reflect the different stress on the periprosthetic bone after implantation of THA in defined ROIs, supporting earlier reported good clinical results of the Spotorno stem and increased loosening rate of threaded acetabular cups after 5 years.

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