Functional outcomes following knee replacement in community-dwelling older adults

Knee replacements are increasingly performed in older adults but uncertainty remains regarding their benefits in the context of age-related decline in physical function and other comorbidities. This study aimed to examine (1) the effect of knee replacement on functional outcomes in the context of age-related decline in physical function and (2) the factors associated with minimal important improvement in physical function after knee replacement in community-dwelling older adults aged ≥ 70 years.

This cohort study was performed within the ASPREE trial, with 889 participants undergoing knee replacement during the trial and 858 age- and sex-matched controls without knee or hip replacement identified from 16,703 Australian participants aged ≥ 70 years. Health-related quality of life was assessed annually using the SF-12, including its physical and mental component summary (PCS and MCS). Gait speed was measured biennially. Multiple linear regression and analysis of covariance were used to adjust for potential confounders.

Participants with knee replacement had significantly lower pre- and post-replacement PCS scores and gait speed compared with age- and sex-matched controls. Participants with knee replacement had significant improvement in PCS score following knee replacement (mean change 3.6, 95% CI 2.9-4.3) while PCS score remaining unchanged in age- and sex-matched controls (-0.02, 95% CI -0.6 to 0.6) during follow-up period. The greatest improvements were observed for bodily pain and physical function. Following knee replacement, 53% of participants experienced minimal important improvement in PCS score (increased by ≥ 2.7), while 24% experienced worsened PCS score (reduced by > 2.7). Participants experiencing improved PCS score postoperatively had significantly lower PCS and higher MCS scores pre-surgery.

Although community-based older adults experienced a significant improvement in PCS scores after knee replacement, their postoperative physical functional status remained significantly lower than age- and sex-matched controls. The degree of preoperative physical function impairment was a strong predictor of functional improvement, suggesting that this could be an important consideration when identifying older people most likely to benefit from knee replacement surgery.