Demostenis Kiritopoulos: Periprosthetic bone and uncemented total hip arthroplasty

Abstract

Uncemented total hip arthroplasty (THA) has continuously increased in recent decades. Biological fixation of the implant is achieved initially by press-fit and secondary by osseointegration. However, uncemented THA is associated with loss of periprosthetic bone mineral density (pBMD), reduced mechanical strength and increased risk of periprosthetic fractures. The goals of this thesis were to study the short-term results of treatment with an antiresorptive drug for an uncemented THA (studies I and II) and the 8-year follow-up of an uncemented acetabular implant (study III). In addition, the reliability, agreement and precision for the periprosthetic standardized uptake value (pSUV) with [18F] fluoride PET/CT (F-PET) were evaluated (study IV). 

We conducted a randomized controlled trial (RCT) to investigate the effect of 2 subcutaneous injections of denosumab, 6 months apart postoperatively, on pBMD by dual-energy x-ray absorptiometry (DXA), pSUV by F-PET and serum markers for bone turnover for an uncemented THA with the collum femoris preserving (CFP) stem and the Continuum cup. Our results show that denosumab prevents early pBMD loss around the stem (study I) and the cup (study II), but the effect is transient upon treatment discontinuation. Additionally, denosumab reduces periprosthetic and systemic bone turnover, but the effect is unsustainable.

Study III is a prospective study to evaluate the 8-year results of the trabeculae-oriented pattern (TOP) cup in terms of implant survival, pBMD measured by DXA and clinical outcomes. We found an overall implant survival for the TOP cup of 83% and that pBMD continued to decrease in the proximal regions around the cup. The clinical outcome in patients with unrevised cups was excellent. 

Study IV is a methodological study investigating F-PET's reliability, agreement and precision. 2 independent observers analyzed all F-PET scans from study II on 2 occasions, with a minimum interval of 3 weeks between each analysis. We found good reliability, high agreement and moderate precision between and within observers.  

This thesis concludes that 2 doses of denosumab effectively prevent pBMD loss around the CFP stem and the Continuum cup while also reducing bone turnover. However, the effect on pBMD is not enduring, and a rebound effect on bone turnover markers appears after treatment discontinuation. Moreover, the TOP cup shows inferior 8-year survival rates compared to other uncemented implants and continuous pBMD loss proximally. Finally, the F-PET of acetabular cups can be reliably performed with strong agreement and moderate precision.