Total hip arthroplasty (THA) could be associated with a higher failure rate in patients after osteonecrosis of the femoral head (ONFH) compared to a patient population with primary osteoarthritis prior THA, especially regarding the acetabular component. One major reason could be the compromised acetabular bone quality. Therefore, we performed a retrospective case matched study to assess: 1) Is there a difference in periprosthetic bone mineral density between patients with an ONFH prior THA and controls? 2) Do patients with an ONFH prior THA have a lower bone mineral density compared to controls? 3) Which region in the periprosthetic bone stock is more likely to present differences in periprosthetic bone mineral density between both groups?

We hypothesized that there is a poorer bone mineral density (BMD) in the periacetabular bone stock in patients with an ONFH prior THA compared to controls receiving a THA due to primary osteoarthritis.

We compared the BMD of 50patients with ONFH to 50controls with primary osteoarthritis prior THA using the same implant in mean 5years after surgery by means of dual energy X-ray absorptiometry (DXA). We analysed 3acetabular ROIs according to DeLee and Charnley in a modified measurement technique.

In ROI 3, representing acetabulum's upper aspect, statistically significant lower BMD values for the ONFH group could be found (P<0.05). No difference was found for the modified ROIs 1 and 2 (respectively medial and lower acetabulum).

The results indicate a poorer periacetabular BMD in patients with ONFH prior THA, which might be responsible for premature loosening of the acetabular cup in THA. Due to a lack of literature, further clinical investigations are required to confirm our results.

III: retrospective case-control study.