Exploring the Impact of Quality of Life on Survival: A Case Study in Total Knee Replacement Surgery

Background. There is growing evidence that quality of life (QoL) has a strong association with mortality. However, incorporation of QoL is uncommon in standard survival modeling. Methods. Using data extracted from a registry of patients undergoing total knee replacement (TKR), the impact of incorporating QoL in survival modeling was explored using 4 parametric survival models. QoL was incorporated and tested in 2 forms, which are baseline and change in QoL due to intervention. Life expectancy and quality-adjusted life years (QALYs) were calculated and comparisons made to a reference model (no QoL) to translate the findings in the context of modeled economic evaluations. Results. A total of 2858 TKR cases (2309 patients) who had TKR between 2006 and 2015 were included in this analysis. Increases in baseline and change in QoL were associated with a reduction in mortality. Compared to the reference model, differences of up to 0.32 life years and 0.53 QALYs were observed, and these translated into a 9.5% change in incremental effectiveness. These differences were much larger as the strength of the association between QoL and mortality increased. Conclusions. This work has demonstrated that the inclusion of QoL measures (at baseline and change from baseline) when extrapolating survival does matter. It can influence health outcomes such as life expectancy and QALYs, which are relevant in cost-effectiveness analysis. This is important because neglecting the correlation between QoL and mortality can lead to imprecise extrapolations and thus risk misleading results affecting subsequent decisions made by policy makers.