Reliability, Construct Validity, and Responsiveness of the Neck Disability Index, Patient-Specific Functional Scale, and Numeric Pain Rating Scale in Patients with Cervical Radiculopathy

Abstract

OBJECTIVE: To examine the psychometric properties of the Neck Disability Index, Patient-Specific Functional Scale, and the Numeric Pain Rating Scale in a cohort of patients with cervical radiculopathy. DESIGN: A single-group repeated-measures design. Patients (n = 165) presenting to physical therapy with cervical radiculopathy completed the Neck Disability Index, Patient-Specific Functional Scale, and Numeric Pain Rating Scale at the baseline examination and at a follow-up. At the time of follow-up, all patients also completed the Global Rating of Change, which was used to dichotomize patients as improved or stable. Baseline and follow-up scores were used to determine the test-retest reliability, construct validity, and minimal levels of detectable and clinically important change for the Neck Disability Index, Patient-Specific Functional Scale, and Numeric Pain Rating Scale. RESULTS: Both the Neck Disability Index and Numeric Pain Rating Scale exhibited fair test-retest reliability, whereas the Patient-Specific Functional Scale exhibited poor reliability in patients with cervical radiculopathy. All three outcome measures showed adequate responsiveness in this patient population. The minimal detectable change was 13.4 for the Neck Disability Index, 3.3 for the Patient-Specific Functional Scale, and 4.1 for the Numeric Pain Rating Scale. The threshold for the minimal clinically important difference was 8.5 for the Neck Disability Index and 2.2 for both the Patient-Specific Functional Scale and Numeric Pain Rating Scale. CONCLUSIONS: In light of the varied distribution of symptoms in patients with cervical radiculopathy, future studies should investigate the psychometric properties of other neck-related disability measures in this patient population.