Uncemented Total Hip Arthroplasty : Aspects on Bone Biology, Implant Fixation, Periprosthetic Bone Remodeling, Bone Mineral Density and Effects of Denosumab

Abstract: Uncemented total hip arthroplasty (THA) is associated with loss of periprosthetic bone mineral density (BMD). The collum femoris preserving (CFP) stem lost 28% of proximal BMD at 2 years. The overall purpose of this thesis was to study the long-term results of the CFP stem in BMD and implant stability (study III) and whether periprosthetic BMD can be preserved with denosumab (study I). Secondary objectives were to evaluate a CT-based technique as an alternative to radiostereometric analysis (RSA) and investigate the reliability, agreement, and precision of periprosthetic [18F]-fluoride PET/CT (F-PET). In study I, a randomized controlled trial, we studied the effect of denosumab on 1) periprosthetic BMD by dual-energy x-ray absorptiometry (DXA), 2) periprosthetic bone formation by F-PET, and 3) serum markers of bone turnover. We found that denosumab prevents early periprosthetic bone loss and reduces periprosthetic and systemic bone turnover. Study II is a methodologic-, multicenter study investigating the precision of low-dose CT-based implant motion analysis (CTMA). We determined the precision of CTMA by repeated measures and found it to be high. In study III we examined the long-term results of the CFP stem. The cohort from a previous, prospective study on the CFP stem was followed up for a minimum of 8 years with DXA and RSA. Periprosthetic BMD was not restored, and further bone loss was seen in the proximal part of the femur; however, the stems appeared stable on RSA. In study IV, we looked at the reliability, agreement, and precision of periprosthetic F-PET. F-PET investigations from study I were analyzed twice by two independent observers, at least 3 weeks apart. Reliability was excellent, agreement was high, and precision was moderate between and within observers. In conclusion, denosumab prevents periprosthetic BMD loss and the CFP stem shows continuous periprosthetic bone loss 8 years after surgery, but the implants remain stable. In addition, this thesis shows that CTMA is a precise method and a viable alternative to RSA. Finally, it demonstrates that periprosthetic F-PET is a reliable method with high inter- and intraobserver agreement.