The aim of this study is to evaluate periprosthetic bone mineral density (BMD) changes in the proximal femur after implantation of the Fitmore compared to the CLS stem.

After power analysis, 140 consecutive patients were prospectively included in the randomisation protocol receiving either a Fitmore short or a CLS straight stem. The short stem was assigned in 57 (37% females) cases and the straight stem in 83 (38% females) hips. Periprosthetic bone mineral density was measured before surgery, 7 days, 3, 12 and 60 months postoperatively, using dual energy x-ray absorptiometry (DEXA). The results of the first postoperative measurement served as the baseline value. Because of the different length of the two prostheses we used adapted Gruen zones to divide the periprosthetic bone in seven regions of interest (ROI) with equal length in the proximal zones 1,2,6 and 7, only the regions 3 and 5 featured different sizes. Clinical results were recorded using the WOMAC and the Harris hip score (HHS).

Inclusion Criteria:

• Primary or secondary osteoarthritis of the hip
• written informed consent
• indication for cementless total hip arthroplasty

Exclusion Criteria:

• previous surgery in the same hip
• femoral fracture
• metabolic bone disease
• drugs affecting bone quality
• contralateral THA within the study period
• infectious disease or bony tumor

Individual participant data will not be shared.