The association between socioeconomic status and joint replacement of the hip and knee: a population-based cohort study of older adults in Tasmania

Background: A socioeconomic gradient exists in the utilisation of total hip replacements (THR) and total knee replacements (TKR) for osteoarthritis. However, the relations between socioeconomic status (SES) and time to THR or TKR is unknown.

Aim: To describe the association between SES and time to THR and TKR.

Methods: 1072 older-adults residing in Tasmania, Australia were studied. Incident primary THR and TKR were determined by data linkage to the Australian Orthopaedic Association National Joint Replacement Registry. At baseline, each participant's area-level SES was determined by the Index of Relative Socioeconomic Advantage and Disadvantage (IRSAD), from the Australian Bureau of Statistics' 2001 census data. IRSAD was analysed in two ways; 1) categorised into quartiles, whereby quartile 1 represented the most socioeconomically disadvantaged group, 2) the cohort dichotomised at the quartile 1 cut-point.

Results: The mean age was 63.0 (±7.5) years, and 51% were women. Over the median follow-up of 12.9 (Interquartile range: 12.2-13.9) years, 56 (5%) participants had a THR, and 79 (7%) had a TKR. Compared to the most disadvantaged quartile, less disadvantaged participants were less likely to have a THR (i.e. less disadvantaged participants had a longer time to THR) (HR: 0.56, 95% CI 0.32, 1.00) but not TKR (HR: 0.90, 95% CI 0.53, 1.54). However, the former became non-significant after adjustment for pain and radiographic osteoarthritis, suggesting that the associations may be mediated by these factors.

Conclusions: This study suggests that time to joint replacement was determined according to the symptoms/need of the participants rather than their SES.