Evaluative Measurement Properties of the Patient-Specific Functional Scale for Primary Shoulder Complaints in Physical Therapy Practice

STUDY DESIGN: Clinical measurement, longitudinal. OBJECTIVES: To assess the test-retest reliability, construct validity, and responsiveness of the Patient-Specific Functional Scale (PSFS) in patients with a primary shoulder complaint. BACKGROUND: Health measurement outcomes have become increasingly important for evaluating treatment. Patient-specific questionnaires are useful tools for determining treatment goals and evaluating treatment in individual patients. These questionnaires have not yet been validated in patients with nonspecific shoulder pain. METHODS: Patients completed the PSFS, the numeric pain rating scale, and the Shoulder Pain and Disability Index at baseline, and after 1 week and 4 to 6 weeks. Test-retest reliability was determined using intraclass correlation coefficients. To assess convergent validity, change scores of the PSFS were correlated with the numeric pain rating scale and Shoulder Pain and Disability Index change scores. Responsiveness was assessed by calculating the area under the curve, the minimal clinically important change, and minimal detectable change, using the global rating of change as an external criterion. RESULTS: Fifty patients (37 men; mean age, 47.7 years) participated in the study. Reliability was high (intraclass correlation coefficient = 0.87; 95% confidence interval [CI]: 0.72, 0.94). The correlations between the change scores of the PSFS and those of the Shoulder Pain and Disability Index and numeric pain rating scale were 0.45(95% CI: 0.17, 0.80) and 0.55 (95% CI: 0.29, 0.73), respectively. The area under the curve for the PSFS was 0.67 (95% CI: 0.51, 0.83). The minimal detectable change and minimal clinically important change were 0.97 and 1.29 points, respectively. CONCLUSION: These results suggest that the PSFS is a reliable, valid, and responsive instrument that can be used as an evaluative instrument in patients with a primary shoulder complaint.