Primary and revision knee arthroplasty in Scotland: projected burden, survivorship, health-related quality of life and cost consequences

Abstract

The overarching aim of this thesis was to investigate the long-term survivorship, health-related quality of life and cost-consequences associated with primary and revision knee arthroplasty (KA) in Scotland. Using novel linkage of national and local datasets, this work provides a population-based evaluation of outcomes across the lifetime of patients undergoing knee replacement. The burden of primary KA in Scotland was projected using national data and multivariable modelling. Prior to the COVID-19 pandemic, annual case volume was expected to rise by 11% between 2020 and 2030 (7,905 (95% confidence intervals (CI) 7,609 to 8,214) in 2020 vs 8,806 (95% CI 8,476 to 9,150) in 2030). However, in 2020, the number of operations fell by 61% due to elective operating suspension. Since then, elective activity in the Scottish National Health Service has slowly recovered but there remains a large volume of patients waiting for surgery across the country. Long-term survival after primary and revision KA was analysed using linked registry and mortality data. Scottish patients who underwent KA had significantly lower mortality rates than age- and sex-matched peers in the general population (standardised mortality ratio (SMR) 0.74 (95% CI 0.73 to 0.74); p < 0.001; SMR 0.83 (95% CI 0.80 to 0.86); p < 0.001, respectively). Using Scottish cohort-specific mortality data, implant survivorship of primary and revision KA was assessed using Kaplan-Meier and Competing Risks methodology. The lifetime risk of revision following primary KA is significantly affected by the competing risk of death. Risk of revision is likely to be influenced by the patient’s sex, their age at surgery, underlying diagnosis, and implant type. Among 8,301 patients undergoing revision KA, approximately one in ten required a further re-revision within ten years (ten-year survival 87.3% (95% CI 86.5-88.1)). Male sex, younger age, infection, and surgery in low-volume hospitals were associated with higher re-revision risk, supporting the centralisation of complex revision procedures to high-volume centres. Health-related quality of life (HRQoL) was assessed using the three-level EuroQol-5 Dimension (EQ-5D-3L) questionnaire. In patients undergoing primary KA, the EQ-5D-3L showed good internal consistency (Cronbach’s α = 0.75 preoperatively, 0.88 postoperatively) and responsiveness, with a minimal clinically important difference (MCID) of 0.085 (95% CI 0.042 to 0.127) and the minimal important change (MIC) for the cohort was 0.289 for the Index score, respectively. Within one year of surgery, HRQoL improved by a mean of 0.32 (SD 0.33) and was restored to levels comparable with age-, sex-, and BMI-matched peers in the general population. Following revision KA, patients experienced meaningful but smaller gains in HRQoL and knee-specific function (One year Oxford Knee Score (OKS) mean change (MC), 12 (95% CI 11 to 14); and EQ-5D-3L MC, 0.214 (95% CI 0.11 to 0.31); Long-term OKS MC, 9 (95% CI 7 to 11); and EQ-5D- 3L MC, 0.172 (95% CI 0.09 to 0.23).). Outcomes were best after aseptic loosening and poorer following revision for infection or instability. A multi-state survival model estimated quality-adjusted life expectancy (QALE) and healthcare costs associated with primary and revision KA. The mean QALE following primary KA for patients aged between 45 and 95 years was 7.93 (95% CI 5.92-9.50). Revision KA was associated with reduced life expectancy and poorer health-status (aseptic revision KA mean QALE 3.89 (95%CI 1.52-6.22); septic revision KA mean QALE 2.70 (95% CI 0.28-5.29)). Compared to population norms for QALE, primary and revision KA were associated with measurable QALY shortfall. In septic revision KA, the magnitude of QALE shortfall would warrant increased severity weighting of QALYs in future health technology assessments. Lifetime cost-utility analysis demonstrated that primary KA is highly cost-effective compared with no surgical treatment, even when accounting for revisio