Background Functional impairment of hip and knee osteoarthritis (OA) and associated co-morbidities can independently impact patient's health state utility (HSU), a useful indicator for valuing health in medico-economic studies.

Objectives This study aimed to examine the respective influence of the evolution of functional impairment and of burden of co-morbidities on a 5-year change in HSU for patients with OA.

Methods 548 patients (Mean age of 61.1 years, 66.6% of women and 68.1% with knee OA) from the KHOALA study with 5 years follow-up were included. Functional impairment, co-morbidities and HSU were measured annually using the WOMAC (0–100) [1], FCI (1–18) [2] and SF-6D (0–1) [3], respectively. First, baseline clinical patterns were identified using hierarchical clustering methods [4]. Then, the role of these patterns as determinants of 5-year change in HSU was analysed using hierarchical mixed models.

Results Two clusters were identified: cluster 1 “Low functional impairment and few co-morbidities” (65.3%) and cluster 2 “Severe functional impairment and many co-morbidities” (34.7%). Compared to the cluster 1, the functional impairment of cluster 2 significantly decreased (-14.5 [-18.1; -10.92]) at 5 year follow up, while the co-morbidity index significantly increased in the two clusters (+0.18 [-0.22; 0.57]). The mean baseline HSU score was 0.66 (0.70 for cluster 1 and 0.59 for cluster 2). Compared to cluster 1, patients in cluster 2 had a significantly higher increased in 5-year HSU (β=+0.0335 [0.0088; 0.0583]) (R²=21%). The difference of 5-year change in HSU was no more significant when adjusted for change in functional impairment (β=+0.0335; p=0.008 vs. -0.0153; p=0.30) (R²=42%) while it remained significant when adjusted for change in co-morbidity index (β=+0.0335; p=0.008 vs. +0.0386; p=0.002) (R²=27%).

Conclusions Cluster analysis showed that patients with severe functional impairment also had high rate of co-morbidities à baseline. The reduction of OA functional impairment is an important determinant of 5-year improvement of HSU while burden of co-morbidities was not associated with change in hip and knee OA HSU. This result highlights the importance of reducing functional impairment in clinical management of patients with hip and knee OA, and gives clues for interpretation of medico-economic analyses.

References

1. Bellamy N, Buchanan WW, Goldsmith CH, Campbell J, Stitt LW. Validation study of WOMAC: a health status instrument for measuring clinically important patient relevant outcomes to antirheumatic drug therapy in patients with osteoarthritis of the hip or knee. J. Rheumatol. 1988;15:1833–40.

2. Groll DL, To T, Bombardier C, Wright JG. The development of a comorbidity index with physical function as the outcome. J. Clin. Epidemiol. 2005;58:595–602.

3. Brazier J, Usherwood T, Harper R, Thomas K. Deriving a preference-based single index from the UK SF-36 Health Survey. J. Clin. Epidemiol. 1998;51:1115–28.

4. Everitt BS. Unresolved Problems in Cluster Analysis. Biometrics. 1979;35:169.

References

Disclosure of Interest None declared