Elsevier

The Spine Journal

Volume 9, Issue 10, October 2009, Pages 802-808
The Spine Journal

Clinical Study
Responsiveness of the Neck Disability Index in patients with mechanical neck disorders

https://doi.org/10.1016/j.spinee.2009.06.002Get rights and content

Abstract

Purpose

Report the test-retest reliability, construct validity, minimum clinically important difference (MCID), and minimal detectable change (MDC) for the Neck Disability Index (NDI).

Study design/setting

Cohort study of patients presenting to outpatient physical therapy clinics.

Patient sample

Ninety-one subjects with a primary complaint of neck pain, with or without concomitant upper extremity (UE) symptoms, who were participants in a randomized clinical trial.

Outcome Measures

NDI and the 15-point Global Rating of Change (GRC) self-report measures.

Methods

All subjects completed the NDI at baseline and at a 3-week follow-up. Additionally, subjects completed the GRC scale, which was used to dichotomize patients into improved or stable groups. Changes in the NDI were used to assess test-retest reliability, construct validity, MCID, and MDC.

Results

Test-retest reliability was moderate for the NDI (intraclass correlation coefficient, 0.64; 95% confidence interval, 0.19–0.84). For the NDI, the MCID was 7.5 points and the MDC was 10.2 points.

Conclusions

The NDI appears to demonstrate adequate responsiveness based on statistical reference criteria when used in a sample that approximates the high percentage of patients with neck pain and concomitant UE referred symptoms. Because the MCID is within the bounds of measurement error, a 10-point change (the MDC) should be used as the MCID.

Introduction

Evidence & Methods

The Neck Pain Disability Index (NPDI) is a popular standardized questionnaire providing a self-report of perceived neck symptoms and impact at one point in time.

The authors found that baseline NPDI scores declined more in subjects who felt, compared to baseline, they were globally “better,” than in subjects who did not feel they were “better.” But there was considerable overlap. The statistically determined minimum detectable change (MDC), calculated from the standard error of measure, appeared to be larger than the minimal clinically important difference in the NPDI.

What constitutes meaningful improvement in spinal disorders remains a controversial area, and statistically derived values based upon a patient's global report of being “better” apparently varies with method of calculation and the population being studied.

The Editors

It is estimated that up to 54% of the population has experienced neck pain within the past 6 months [1], with up to 42% seeking care from general practitioners [2]. Fifteen percent of a physical therapist's caseload consists of patients with neck pain [3]. Several self-report functional outcome or disability measures have been developed for the assessment of disability in patients with neck pain [4], [5], [6], [7], [8], [9], [10]. Of interest to clinicians is the clinical utility of self-report measures to accurately reflect patient-perceived status and identify when that status has changed through a course of treatment.

The Neck Disability Index (NDI), originally modeled after the Oswestry Low Back Pain Disability Questionnaire [4], [11], is the most studied and well established of the outcome measures for neck pain [12] and assesses both subjective symptoms and activities of daily living. Several researchers [4], [8], [13], [14] have assessed the reliability and validity of the NDI. Three studies [8], [13], [15] have reported on the responsiveness of the scale or the ability of the scale to accuretly detect when change has indeed occurred [16]. Responsiveness is often reported in two ways. The first is the minimum detectable change (MDC), that is defined as a change in a patient's score that is greater than measurement error [17]. The second is the minimum clinically important difference (MCID) or the smallest change in an instrument that is perceived to be beneficial by the patient and thus would bring about a change in patient management [18]. Prior MDC scores for the NDI have been reported to be between 4.2 and 9.8 raw score points [8], [13], [15]. Prior MCID scores for the NDI have been reported to be between 5 and 9.5 raw score points [13], [15].

Sixty-five percent of patients with pain referable to the cervical spine report both axial and upper extremity (UE) radicular symptoms [19]. However, prior reports of the psychometric properties of the NDI have yet to be reported in a sample which approximates this high percentage of patients with neck pain and concomitant UE referred symptoms. Therefore, the primary purpose of this study was to report the psychometric properties of the NDI in a large sample of patients with a primary complaint of mechanical neck pain, presenting with or without concomitant UE radicular symptoms. A secondary purpose was to assess if there is a difference in the amount of change in NDI scores relative to baseline scores between patients with and without unilateral UE symptoms who were rated as improved, as well as between those rated as stable.

Section snippets

Subjects

This study is a secondary analysis of a larger multicenter randomized clinical trial of physical therapy interventions for patients presenting with mechanical neck pain [20]. In the overall trial, patients were randomized to receive manual physical therapy and exercise or a treatment approach comprising advice to remain active, range-of-motion exercise, and subtherapeutic ultrasound. For the purpose of this secondary analysis, treatment groups were collapsed into a single cohort. Patients were

Neck Disability Index

The NDI [4], [11] is a 10-item, 50-point index that assesses different aspects of daily functioning in patients with neck pain. The NDI assesses four items regarding subjective symptoms (pain intensity, headache, concentration, sleeping), four items regarding activities of daily living (lifting, work, driving, recreation), and two items regarding discretionary activities of daily living (personal care, reading) [8], [13]. Each item is scored 0 to 5, with the total reported as either a raw score

Data analysis

Patients with an average GRC rating ≥3 (“somewhat better”) were considered to have improved. Patients with an average rating <3 to >−3 were considered to have remained stable. Patients with an average rating of ≤−3 (“somewhat worse”) or smaller were considered to have worsened. Because no patients were classified as worsened in our sample, we classified all the patients into two groups, improved and stable, for data analysis.

Patient variables for the improved and stable groups were compared at

Results

Data from 91 patients (mean age, 47.8 years; SD, 14.6 years; 61 female) were used in this analysis. The mean GRC (average of patient/clinician) for all patients was 3.9 (SD, 2.3), with an ICC of r=0.69 (p<.000) between the patient and clinician GRC. At the 3-week follow-up, 66 patients (73%) were classified as having improved (≥3), and 25 patients (27%) were classified as remaining stable (<3 to >−3). No patients were classified as worsening. These groups did not differ in their baseline

Discussion

The results of this study show that a change of 7.5 out of 50 points (or 15 points if referencing a 100-point scale) is the MCID for the NDI when used to collectively assess outcomes in patients presenting with primary mechanical neck pain both with and without concomitant UE symptoms. However, the MCID is within the bounds of measurement error as indicated by an MDC of 10.2 points [26]. These results are similar to those of Cleland et al. [15] and are higher than those previously reported by

Conclusions

The NDI demonstrates satisfactory responsiveness in our study. In application to clinical practice, one should consider NDI changes of 10 points to be clinically meaningful for patients with mechanical neck pain presenting both with and without concurrent UE symptoms.

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    FDA device/drug status: not applicable.

    Author disclosures: none.

    The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the U.S. Air Force, U.S. Public Health Service, U.S. Army, or Department of Defense.

    The study was approved by the Brooke Army Medical Center/Wilford Hall Medical Center Joint Institutional Review Board.

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