Outcomes of cemented and hybrid primary total hip arthroplasty in osteoarthritis: A New Zealand regional study

Abstract

Introduction: Primary total hip arthroplasty (THA) for osteoarthritis (OA) success is typically assessed using implant survival as the primary outcome; however, revision surgery alone underestimates the true burden of suboptimal outcomes (e.g., pain or poor function). Secondary outcomes, or patient-reported outcomes (PROMs), therefore provide a complementary assessment of THA success. During the last two decades, fully cemented THAs have been progressively replaced by uncemented ones, despite limited long-term comparative evidence. Although national registry data allow analysis of broad implant category types, they may lack implant and PROM detail compared to regional registries. This Thesis evaluates whether changes in implant design and fixation strategy have translated into significant and meaningful improvements in implant survival and patient outcomes in the Bay of Plenty region of Aotearoa New Zealand (NZ).

Aims: This Thesis aimed to evaluate long-term survival and PROMs of an early generation cemented, modern cemented, and modern hybrid primary THA for OA, and identify patient factors or funding source associated with these outcomes. The work first synthesised existing evidence comparing cemented and hybrid fixation. It then compared survival between the earlier generation THA and its modern cemented successor of the same lineage. Thereafter, the work identified long-term PROMs in earlier generation cemented THA and then compared 10-year PROMs between the two cemented THA generations. Finally, survival and PROM outcomes of the hybrid THA were compared with the modern cemented. Influential patient and funding factors of primary and secondary outcomes were identified across all studies.

Methods: This Thesis comprised a systematic literature review and linked retrospective cohort studies using prospectively collected arthroplasty survival and PROM data from the NZ joint registry (NZJR) and Tauranga Orthopaedic Research Inc. registry for the Bay of Plenty region. Patients undergoing primary THA for OA between 2003 to 2023 with earlier generation cemented, modern cemented, or modern hybrid THAs were included. PROMs included the Oxford Hip Score (OHS), McMaster University Osteoarthritis index (WOMAC), and Veterans Rand 12-item health survey (VR-12). Baseline differences were addressed using propensity score weighting. Implant survival was analysed using Cox regression, and PROMs were analysed longitudinally including changes from baseline. Multivariable models examined the influence of sex, ethnicity, age at surgery, body mass index (BMI), American Anesthesiologist Society (ASA) rating, and funding source (public versus private) on outcomes.

Results: In the literature, five studies compared survival and three compared PROMs between cemented and hybrid primary THA for OA. Survival outcomes were no different between THAs in three studies, but cemented survival was superior in two studies. PROMs were no different in the three available studies.