Neck Solutions

Disability in subacute whiplash patients: Usefulness of the Neck Disability Index

From: Spine J. 2008 August ;33(18)630-635

Whiplash describes a process of hyperextension and hyperflexion of the cervical musculature that may result from motor vehicle collisions. The incidence of whiplash has been estimated to be of 1 case per 1000 habitants per year in Western societies, nevertheless available studies report conflicting rates. Symptoms associated with whiplash problems typically resolve in a relatively brief time (days or weeks), but chronic pain, and long-term disability may occur in 10% to 40% of the cases.

The prevention and treatment of chronic disabling pain in whiplash patients has shown to be elusive. On the one hand, predictive factors of chronic disabling problems in whiplash patients are far from being completely elucidated. Although one can hypothesize that factors from different levels (i.e., physiology, thoughts, feelings, and behavior) and units (i.e., individual, dyad, and context) of analysis play a role, very few and inconsistent findings are available. On the other hand, there is limited evidence about what is the most beneficial treatment for whom and under what circumstances. The use of many different outcome variables and assessment instruments may be responsible, in part at least, of the problems encountered in this area of research to compare results across studies and extract definitive conclusions.

One instrument that could be used as a standardized outcome in the whiplash field is the neck disability index. The neck disability index was constructed to assess disability due to neck pain, especially in whiplash injuries. It is a 10-item self-report questionnaire derived, in part, from the Oswestry low back pain index, assessing the extent to which neck pain interferes with patients’ daily functioning in ten different areas. Although other measures are available to assess disability in patients with neck pain, and recently, a specific measure for whiplash patients has been developed (the Whiplash Disability Questionnaire), the neck disability index has become one of the most used questionnaires in the neck pain field, and recommended to be used in the whiplash field because of its positive assets and strengths. Specifically, the neck disability index has adequate psychometric properties: it has shown good internal consistency, test-retest reliability, and construct validity. Another interesting and valuable characteristic of this measure is that it has been translated into several languages (i.e., Dutch, French, Korean, Brazilian-Portuguese, Swedish, and Turkish), with these new versions of the instrument showing appropriate psychometric values too. Thus facilitating transcultural studies in this field.

Although the neck disability index has shown some good psychometric properties, has been translated into different languages, and extensively used with whiplash patients, its usefulness has not been assessed in this population. Only a few studies examining the psychometric properties of the neck disability index have included small subsamples of whiplash participants, but none of them have studied the neck disability index in a sample of whiplash patients. It is also worthwhile to mention that while the neck disability index has shown acceptable psychometric properties in neck pain patients, its factorial structure has rarely been analyzed. Indeed, just 3 studies have addressed this issue, and shown inconsistent results. Hains et al found a unique factor for the original version of the neck disability index, which was later replicated with the Brazilian-Portuguese version of the neck disability index. More recently, however, Wlodyka-Demaille et al found a 2-factor structure for the French version of the neck disability index.

The main aim of our work was to study the psychometric properties of the neck disability index, including its factorial structure, in a sample of Catalan-speaking subacute whiplash patients, and its usefulness. Specifically, the study was designed to analyze the following psychometric properties of the neck disability index: (1) items properties, (2) factorial structure, (3) internal consistency, and (4) criterion-related validity.

The aim of this investigation was to study the usefulness of the neck disability index with subacute whiplash patients. Our work was designed to assess the psychometric properties of the neck disability index too, with a special emphasis in its factor structure. The results are in agreement with previous reports that showed that the neck disability index has good psychometric properties. Briefly said, the Catalan version of the neck disability index is a measure with robust psychometric properties, useful to assess disability in patients with subacute whiplash problems: (1) it is easily self-administered as it so has been supported by a very low rate of missing values, (2) individual items and total scores are normally distributed, (3) the internal consistency is good, and (4) the criterion-related validity has generously been supported too, by the correlations with the outcome variables (i.e., pain intensity, pain interference, and depression).

In relation to the factor structure of the neck disability index, our results are in agreement with Wlodyka-Demaille et al’s work, who also found a 2-factor structure. Specifically, they found that the items concerning personal care, lifting, concentration, work, driving, and recreation mainly loaded in a factor which they labeled as function and disability. The rest of the items, those referring to neck pain, reading, headache, and sleeping mainly loaded in a factor which they labeled as pain intensity. There are, however, 2 differences between the 2-factor structure reported in this study and the one found by Wlodyka-Demaille et al. First, Wlodyka-Demaille et al found that although item 6 (concentration) had loadings in both factors the highest loading was in the factor that they called function and disability. In our study, however, this item showed the highest loading on the other factor, the one which they called pain intensity. On the basis of our results, we have labeled the 2 factors in a slightly different way. Thus, the subscale originally referred to as pain intensity by Wlodyka-Demaille et al has been relabeled as pain and interference with cognitive functioning. This subscale besides the items that allude to neck pain and headache intensity, contains items that allude to the extent to which neck pain interferes with a person’s cognitive functioning (e.g., concentration and reading). The other factor that is almost equivalent to that labeled as function and disability by Wlodyka-Demaille et al, except for item 6, has been relabeled as functional disability. In this subscale, the items mainly refer to the extent to which neck pain influences on the performance of a person’s usual physical activities (e.g., work and lifting).

The second difference has to do with the correlation between the 2 factors. Wlodyka-Deamille et al used an orthogonal rotation procedure, so they did not allow the factors to correlate, whereas we have used an oblique rotation procedure and found, in fact, that the 2 factors are highly correlated.

Although our results showed that the Catalan version of the neck disability index is a useful instrument to assess disability in patients suffering from a subacute whiplash problem, further research is needed to determine the factor structure of the neck disability index. If future studies confirm this 2-factor structure, this could have clinical and research implications. That is, specialists could not only use the total neck disability index scores but also benefit from the 2 more specific scores of the subscales. The subscale scores would allow more concrete analyses, and explore specific relationships with potential relevant outcomes (e.g., pain intensity, quality of life). Similarly, additional works are warranted to analyze additional psychometric properties, that is, test-retest reliability and construct-related validity.

The neck disability index was developed to assess neck pain related disability, and several relevant components of whiplash injuries are left out of the scope and interest of this instrument (e.g., headache, shoulder pain, low back pain, dizziness). Moreover, important issues that have shown to be relevant in whiplash injuries (e.g., sleep, concentration, emotional impairments) are not targeted by the neck disability index. Thus, researchers and clinicians that would like to go beyond the boundary and scope conditions for which the neck disability index was created would have to use it within a comprehensive net of assessment instruments taping those additional levels and/or units of interest.