Modeling the need for hip and knee replacement surgery. Part 1. A two‐stage cross‐cohort approach

Abstract

Objective. To explore inequalities in the need for hip/knee replacement surgery using a 2-stage cross-cohort approach. Methods. In the first stage, a small-area population-based survey, the Somerset and Avon Survey of Health, was used to provide a high-quality measure of need for hip/knee replacement using the New Zealand (NZ) score. Receiver operating characteristic curve analyses were used to validate a simplified NZ score, excluding information from clinical examination. In the second stage, a nationally representative population-based survey, the English Longitudinal Study of Ageing, was used to explore inequalities in need for hip/knee replacement using the simplified NZ score. Multilevel Poisson regression modeling was used to estimate rates of need for surgery. Exposures considered were age, sex, social class, ethnicity, obesity, Index of Multiple Deprivation 2004 deprivation quintiles, rurality, and ethnic mix of area. Results. Rates of need for hip/knee replacement increase with age and are lower in men than in women (rate ratio [RR]0.7, 95% confidence interval [95% CI] 0.6 -0.9 for hips; RR 0.8, 95% CI 0.7-1.0 for knees). Those of lowest social class have greater need. Need was greatest for people living in more deprived areas. Individual ethnic group did not predict the need for surgery. For hip replacement, there was no rurality effect; for knee replacement, those in town and fringe areas had greater need. Obesity was a strong predictor of need for surgery (RR 2.3, 95% CI 1.9 -2.8 for hips; RR 2.4, 95% CI 2.0 -2.8 for knees). Conclusion. This study provides evidence of greater variations of inequalities in need for hip/knee replacement than previous studies. Further research should explore geographic variation and produce small-area estimates of need to inform local health planning. It is important to complement data on need with willingness to undergo surgery.

Obesity and the Relative Risk of Knee Replacement Surgery in Patients With Knee Osteoarthritis: A Prospective Cohort Study

“…In studies using general population cohorts (not specifically diagnosed as having OA), obesity (defined as a BMI of $30 kg/m 2 ) was associated with a 10-fold higher risk of knee replacement (24), and a relative risk of 2.4 (95% CI 2.0-2.8) for the need for surgery based on pain, function, and clinical assessment (23). A Swedish study found similar results using a lower BMI cutoff ($25 kg/m 2 ), with an RR of 6.9 for women and 4.4 for men compared to subjects with a normal BMI (42).…”

Involvement of different risk factors in clinically severe large joint osteoarthritis according to the presence of hand interphalangeal nodes

“…Cases of total joint replacement represent only a fraction of the overall population with severe, symptomatic large joint OA. Among subjects over the age of 60 years in the UK, the prevalence of the need for total joint replacement (excluding those who actually receive total joint replacement) is between 12.4% and 16% (20, 21), and the prevalence of receipt of total joint replacement is ∼6% (20), which, when added to the prevalence of the need for total joint replacement, yields a prevalence of total joint replacement with or without receipt of surgery of between 18.4% and 22%. Thus, 27–33% of individuals who require a total joint replacement receive one.…”

“…Our results should be applicable to at least one‐fourth of individuals with severe, symptomatic large joint OA, which is a high enough proportion of such cases to be of merit and is consistent with the rates of transition from hip pain to being listed for total joint replacement (23%) in primary care patients over a 4‐year period in a prospective UK cohort study (22). Factors such as wealth, education, geographic region, smoking status, obesity, and sex (21, 23) have been reported to influence rates of access to total joint replacement, and recent studies have revealed considerable heterogeneity in the radiographic severity, functional disability, and pain in candidates for total joint replacement (24). Thus, for example, patients undergoing total joint replacement may be generally fitter than people with both clinically severe large joint OA and severe comorbidity, and our conclusions may not hold among nonsurgical severe large joint OA cases.…”

Modeling the need for hip and knee replacement surgery. Part 2. Incorporating census data to provide small‐area predictions for need with uncertainty bounds

“…To identify whether or not a person is in need of joint replacement surgery in the ELSA data set, we used the New Zealand score out of 80, with a cutoff of 48 (19). Different choices of threshold will classify those with more/less severe disease as being in need of surgery.…”

“…We have previously described how a 2‐stage cross‐cohort approach can be used to identify people in need of hip and knee replacement and explored inequalities in the need for surgery (19). Briefly, the English Longitudinal Study of Ageing (ELSA) is a nationally representative population‐based sample of 11,392 people age ≥50 years living in private households in England.…”