Ændringer i knoglemineraldensitet i den proksimale femur 18 måneder efter total hoftealloplastik med Exeter-stem

Introduction: Total hip arthroplasty (THA) changes the strain distribution pattern in the proximal femur, decreasing the stress in the proximal part of the femur and increasing the stress at the distal part of the femoral component. The purpose of this study was to quantify periprosthetic changes in BMD 18 months after insertion of a THA with cemented Exeter stem. Materials and methods: Twenty-six women (55-80 years of age) undergoing THA with Exeter stem were included in this study. BMD was measured in seven regions of interest according to Gruen et al., using DXA postoperatively and after 18 months of follow-up. At the same time, the contralateral hip and lumbar spine were scanned. Results: At follow-up no arthoplasties were malfunctioning. A significant decrease in BMD ranging from 7.4 ± 0.7% to 13.6 ± 2.0% was present in zones 2, 3, 6 and 7 (p < 0.005). No significant changes were seen in BMD in zones 1, 4 and 5, in the hip, or in the lumbar spine. The total periprosthetic BMD decreased by 5.8 ± 1.3% over the course of 18 months (p < 0.005). Discussion: Significant bone loss was seen in zones 2, 3, 6 and 7 following THA. The degree of bone loss was similar to that found with other types of implants and seems to be related to the changes in stress pattern within the proximal femur. DXA is a useful tool for monitoring changes in the proximal femur after alloplastic surgery.