We present the results of a prospective longitudinal follow-up study of Dual X-ray Absorptiometry (DXA) measurements of the evolution of bone mineral density (BMD) of acetabulum and femur in 86 patients who underwent total hip arthroplasty (THA). A standard uncemented cup and intra-operatively manufactured stem prosthesis was used in all patients. Stem fixation was determided by the bone quality Thirthy patients received cementless and 56 patients received cemented stem prosthesis. Post-operative DXA scans were obtained in peri-prosthetic bone at 10 days, 6 weeks, 3, 6 and 12 months after THA. Peri-prosthetic BMD values in the proximal femur were obtained in the 7 Gruen zones. In the acetabulum a 4 region of interest model (ROI) was used.

Bimodal significant femoral BMD changes are found in all Gruen zones except for zone 1 of the cemented group where an immediate recovery is observed. The recovery mostly starts after 6 months of follow-up and the highest remodelling is found in the calcar region reaching even values of −16% at 6 months but no statistical significance was observed between the two groups. Significant linear losses (p< 0.0001) are observed in the pelvis region independent of type of fixation except the opposite change (p< 0.01) in the inferior region observing an immediate recovery in the uncemented group.

We compared the impact of a cemented stem with a non cemented stem on the bone remodelling of the cup and found that there was a correlation between the type of fixation and the mode of remodelling at the acetabular level. This suggest that a parameter such as the flexibility my have an influence on the bone remodelling at the acetabulum level. The pattern of bone remodelling observed on the different Gruen zones reflects the local load transfer to peri-prosthetic bone.