Validation of a new symptom outcome for knee osteoarthritis: the Ambulation Adjusted Score for Knee pain.

OBJECTIVE: Validation of a symptom measure for early knee OA may help identify new treatments and modifiable risk factors. Symptom measures that consider pain in the context of activity level may provide better discrimination than pain alone. Therefore, we aimed to compare sensitivity to change for radiographic progression between Ambulation Adjusted Score for Knee pain (AASK), which accounts for self-reported ambulation, and Western Ontario McMaster Osteoarthritis (WOMAC) knee pain score.

DESIGN: Participants were assessed annually up to 48 months using WOMAC, Physical Activity Scale for the Elderly (PASE) ambulation, and knee radiographs. AASK was defined as ((WOMAC pain) + 1)/((average daily hours of walking) + 1). Radiographs were scored for Kellgren-Lawrence (KL) grade. Linear regression, stratified by OA status, evaluated relationships between changes in AASK and WOMAC pain and KL grade over time.

RESULTS: For 4191 people (8030 knees), the mean age was 61.2 (+ 9.2) years old and BMI was 28.6 (+ 4.8) kg/m2 ; 58% female. Over 40% of knees had WOMAC pain scores of 0; by design, no knees had AASK scores of 0. Annual changes in AASK were more sensitive to changes in KL than changes in WOMAC in those without baseline OA (0.20 and 0.16 change per unit KL change, p = 0.005 and 0.070 respectively), but performed similarly in knees with OA.

CONCLUSION: AASK is simple to assess using existing validated questionnaires. AASK performs well in individuals with and without OA and should be considered in clinical trials and observational studies of early knee OA.