Reliability and Responsiveness of the Lower Extremity Functional Scale and the Anterior Knee Pain Scale in Patients With Anterior Knee Pain

STUDY DESIGN: Prospective methodological study of repeated measures using a sample of consecutive patients. OBJECTIVE: To determine the test-retest reliability and responsiveness of the Anterior Knee Pain Scale (AKPS) and the Lower Extremity Functional Scale (LEFS) in patients with anterior knee pain. BACKGROUND: Anterior knee pain is one of the most common orthopedic complaints affecting the knee. Yet there is currently no self-report outcome measure that has well-established reliability and responsiveness, specifically for this population. As a result, clinicians and researchers may be making inappropriate conclusions regarding patient outcomes by using questionnaires that are misleading. METHODS AND MEASURES: This multisite study involved 30 patients from 4 outpatient physical therapy clinics in Dallas, TX (24 women, 6 men; age range, 16-50 years; mean+/-SD age, 35.2+/-9.1 years). Patients receiving physical therapy for a chief complaint of anterior knee pain completed the AKPS and LEFS at their initial appointment and again 2 to 3 days later. Upon completion of physical therapy, the patients completed the AKPS, LEFS, and a global rating of change form. The treating therapist also completed a global rating of change form at the patient's final visit. The mean of the patient's and therapist's global rating of change was used as the criterion measure of change. RESULTS: Test-retest reliability was high for both questionnaires (ICC2,1 = 0.95 for the AKPS and 0.98 for the LEFS). A significant correlation was found between the criterion measure of change and both questionnaires. Receiver-operating characteristic curve analysis revealed that both questionnaires were moderately responsive with the area under the curve slightly higher for the LEFS (0.77) than the AKPS (0.69). CONCLUSION: The LEFS and the AKPS both demonstrated high test-retest reliability and appear to be moderately responsive to clinical change in patients with anterior knee pain. Reliability and responsiveness were slightly higher in the LEFS than the AKPS. Further research is needed to determine if these measures could be modified, or new measures created, to produce an even more sensitive tool for this population.