Fixation and Migration in Total Hip Arthroplasty

Abstract

Early implant migration in cemented total hip arthroplasty (THA) is a strong surrogate for later aseptic loosening; thus, precise, repeatable micromotion measurements are central to safe, stepwise evaluation of new cements and emerging imaging methods. This thesis addresses two linked needs: (i) clinical and experimental validation of low‑dose CT–based radiostereometric analysis (CT‑RSA) compared to marker‑based RSA (MBRSA), and (ii) RSA‑based, randomized comparison of a reformulated gentamicin‑loaded cement (Refobacin Bone Cement R, 2016) versus the widely used Palacos R+G. Study I was a prospective sub‑study that showed that CT‑RSA matched MBRSA for assessing acetabular cup migration, with precision and method agreement within clinically relevant bounds at 1 year. Study II was a single‑centre randomized comparison of Refobacin Bone cement R and Palacos R+G, also examining two vacuum mixing systems. 2‑year femoral stem subsidence, cement mantle quality, stem alignment, and patient‑reported outcomes (PROM) were similar across groups, no revisions occurred, and mixing system choice had no measurable effect. Study III was a second prospective sub‑study that found CT‑RSA comparable to MBRSA for measuring femoral stem subsidence at 1 year, meeting a predefined minimal important difference. Moreover, CT‑RSA demonstrated excellent intra‑ and inter‑observer reliability. Study IV was an experimental phantom study with controlled known translations that confirmed sub‑tenth‑millimetre precision and accuracy for CT‑RSA and excellent observer reliability; performance was maintained even after coordinate‑system transformation. In conclusion, across clinical and experimental settings, CT‑RSA provided cup and stem migration measurements comparable to MBRSA, with good clinically relevant precision and excellent intra‑/interobserver reliability, while enabling a marker‑free workflow. The reformulated Refobacin Bone Cement R performed equivalently to Palacos R+G at 2 years with a force‑closed stem and cement and mixing system choice did not influence migration or PROM. Taken together, these studies support CT‑RSA as a validated alternative for early migration surveillance in cemented THA and reaffirm the value of RSA‑based, stepwise introduction when assessing new cements and measurement methods.