Introduction: Implantation of a THA changes the strain distribution pattern in the proximal femur, with a massive loss of stress in the proximal part of the femur and an increase in stress at the distal part of the femoral component.

Aim: The purpose of this study was to quantify the changes in BMD during long-term follow-up, i.e. five years, after insertion of the collarless, two-side conical, cemented Exeter stem.

Material & Methods: Eighteen patients (all women), aged 55 to 80 years, undergoing THA were included in the study after informed consent. BMD was measured in 7 regions of interest according to Gruen et al., using Dual Energy X-ray Absorptiometry postoperatively, after 18 and 60 months of follow-up. At the same time, the contra lateral hip and spine were scanned. Results were tested using Wilcoxon matched-pairs signed-rank test. P values below 0.05 were considered significant.

Results: During the first 18 months, a significant decrease in BMD was present in Gruen zones 2, 3, 6, and 7. No significant changes were seen in BMD of the zones 4, and 5 in the contra lateral hip, nor at the spine. In zone 1 there was a small but significant rise in BMD.

From 18 to 60 months of follow up we observed a significant rise in BMD in all Gruen zones but zone 4 and 7. Despite this the total periprostetic BMD decreased during the study periode. There was no significant decrease in BMD in the contra lateral hip. In the spine, we observed a significant rise in BMD.

Conclusion: During short-term follow-up (i.e. 18 months) after THA, BMD decreased in Gruen zones 2, 3, 6 and 7. The bone loss is similar to findings in other implants and seems to be related to the changes in stress pattern within the proximal femur. During long-term follow-up (i.e. 5 years) BMD increased again in these zones, however, BMD remained lower than baseline.