Association between knee symptoms, change in knee symptoms over 6-9 years, and SF-6D health state utility among middle-aged Australians

Objectives: Health state utilities (HSUs) are an input metric for estimating quality-adjusted life-years (QALY) in cost-utility analyses. Currently, there is a paucity of data on association of knee symptoms with HSUs for middle-aged populations. We aimed to describe the association of knee symptoms and change in knee symptoms with SF-6D HSUs and described the distribution of HSUs against knee symptoms' severity.

Methods: Participants (36-49-years) were selected from the third follow-up (completed 2019) of Australian Childhood Determinants of Adult Health study. SF-6D HSUs were generated from the participant-reported SF-12. Association between participant-reported WOMAC knee symptoms' severity, change in knee symptoms over 6-9 years, and HSUs were evaluated using linear regression models.

Results: For the cross-sectional analysis, 1,567 participants were included; mean age 43.5 years, female 54%, BMI ± SD 27.18 ± 5.31 kg/m². Mean ± SD HSUs for normal, moderate, and severe WOMAC scores were 0.820 ± 0.120, 0.800 ± 0.120, and 0.740 ± 0.130, respectively. A significant association was observed between worsening knee symptoms and HSUs in univariable and multivariable analyses after adjustment (age and sex). HSU decrement for normal-to-severe total-WOMAC and WOMAC-pain was - 0.080 (95% CI - 0.100 to - 0.060, p < 0.01) and - 0.067 (- 0.085 to - 0.048, p < 0.01), exceeding the mean minimal clinically important difference (0.04). Increase in knee pain over 6-9 years was associated with a significant reduction in HSU.

Conclusion: In a middle-aged population-based sample, there was an independent negative association between worse knee symptoms and SF-6D HSUs. Our findings may be used by decision-makers to define more realistic and conservative baseline and ongoing HSU values when assessing QALY changes associated with osteoarthritis interventions.