The reliability, validity, interpretability, and responsiveness of the Norwegian version of the Anterior Knee Pain Scale in patellofemoral pain

Purpose To determine the reliability, validity, responsiveness, and interpretability of the Norwegian Anterior Knee Pain Scale (AKPS) in patients with patellofemoral pain (PFP). Methods The AKPS was translated into Norwegian. One hundred and twelve patients with PFP participated in a randomized controlled trial. Fifty stable patients completed the AKPS at a one-week interval for test-retest reliability. Smallest detectable change (SDC) and floor/ceiling effects were evaluated. Validity and responsiveness were assessed using hypothesis testing for correlations with other scores and known-group validity. Minimal important change (MIC) and responsiveness were evaluated at three months. Results Intraclass correlation coefficient (ICCagreement) for sum score was 0.83. Smallest detectable change was 13. No floor/ceiling effects were found for total score, but ceiling effects were found on eight of 13 individual items. Hypothesis testing for construct validity and responsiveness was largely confirmed but correlations were moderate to low. The MIC was 11. Area under receiver operating characteristic curve was 0.66 (95% CI 0.56-0.77) indicating moderate responsiveness. Conclusions The Norwegian AKPS had comparable measurement properties to other versions, with acceptable reliability and construct validity. We found moderate responsiveness which may be related to ceiling effects on several items. Implications for rehabilitation The Anterior Knee Pain Scale (AKPS) is a commonly used outcome measure in patellofemoral pain, having acceptable reliability and moderate responsiveness. A change in AKPS total score of 11 points would be considered important by the patient, although changes up to 13 points may be due to measurement error. The AKPS has limitations including ceiling effects on most individual items in this patient population, and low correlation between pain and AKPS that questions the validity of the score. A revision of the score should be considered.