Rasch Analysis of Psychometric Properties of Knee Pain and Function Scales in Adults with Non-Traumatic Non-Surgical Patellofemoral Pain: Implications for Military Personnel

Abstract

Introduction This study evaluates the psychometric properties of 3 widely used assessment tools for adults reporting patellofemoral pain (PFP): The Anterior Knee Pain Scale (AKPS), the Knee Injury and Osteoarthritis Outcome Score-Patellofemoral subscale (KOOS-PF), and the Pain Self-Efficacy Questionnaire (PSEQ), applying Rasch analysis to enhance measurement accuracy. Also, correlations among scores from these instruments were evaluated. Evaluating these tools for PFP is crucial because of their relevance to the military population. Materials and Methods Data from 160 participants with non-traumatic non-surgical PFP (70% female, average age 23) across 5 studies were analyzed using the Rasch measurement model to assess item fit, unidimensionality, and reliability. Relationships were estimated with Spearman correlation. Results The AKPS exhibited low reliability (0.61) and poor unidimensionality, with only 39.7% of variance explained, suggesting that it is not consistently effective in measuring pain severity. Two items (AKPS8 - prolonged sitting and AKPS10 - swelling) were inconsistent with the Rasch model, further questioning its utility in differentiating self-reported function. The KOOS-PF showed strong person reliability (0.84). The PSEQ demonstrated adequate reliability (0.79) and unidimensionality, with 56.8% of the raw variance explained. However, its ability to differentiate between high levels of self-efficacy was limited as a result of ceiling effects, suggesting that including more challenging items could improve its precision. Scores on AKPS and KOOS-PF had the strongest correlation, whereas PSEQ had weaker correlations with AKPS and KOOS-PF. Conclusions Although the KOOS-PF and PSEQ are reliable tools for assessing self-reported knee pain severity and self-efficacy in managing pain, the AKPS requires refinement. This study underscores the importance of Rasch analysis for improving assessment tools, especially for military personnel affected by non-traumatic non-surgical PFP. Considering the psychometrics strengths discussed in relation to the use of KOOS-PF and the issues identified in the AKPS, clinicians may consider focusing on using only KOOS-PF instead of both instruments.