Validity of the Neck Disability Index and Neck Pain and Disability Scale for measuring disability associated with chronic, non traumatic neck pain
Neck pain has a lifetime prevalence of about 70% in the general population. Although acute neck pain often resolves, about 19% of the population may suffer from chronic neck pain at any given time. Measurement of the impact of neck pain on the sufferer presents a challenge due to the variability between patients in pain intensity, and the effect of the disorder on physical and psychological functions. Measures of pain intensity and tissue sensitivity have been used to quantify the sensory dimension of neck pain disorders, while range of motion and muscle function has been used to measure impairments of physical function. However, recent recommendations place greater emphasis on functional status and quality of life more broadly, in the evaluation of neck pain disorders.
Measurement of function has been a developing theme in neck pain research as this shifts the focus away from signs and symptoms towards the specific effects of the symptoms on patient function. In relation to neck pain, this includes neck function, physical function more generally, and psychological function. A range of neck pain specific questionnaires have been developed for this purpose, and have been incorporated into recent clinical studies. The value of questionnaires is dependent on a range of factors but of primary importance is the validity, particularly in relation to construct and content. A recent review of neck pain specific questionnaires concluded that most have not been extensively validated, and recommended a comparative study to better define the psychometric properties of the commonly used instruments.
The Neck Disability Index is the most commonly used questionnaire for the measurement of neck pain disability. It was originally developed to evaluate the activities of daily living in patients with disabling neck pain, particularly that resulting from whiplash trauma. The Neck Disability Index includes 10 questions of which 7 examine functional activities, 2 ask about symptoms and the final question considers concentration. The Neck Pain and Disability Scale was developed to provide clinicians with a tool to assess the multi dimensional effects of the neck pain disorder. The scale consists of 20 questions relating to 4 domains (neck function, pain intensity, emotion/cognition and activities of daily living) which look at the effects of the neck pain disorder on patients’ physical and emotional functions. The potential limitation of these questionnaires, and others with fixed questions, is that they constrain the scope of the evaluation to the specific issues included. Therefore, the questionnaire may include questions not relevant to some patients, and may not include issues of importance.
An alternative to the fixed-item questionnaire are the patient specific techniques which require patients to generate their own, possibly unique, set of problems or items. The patient specific methods offer the advantage of identifying the problems or issues relevant to each individual, and are therefore consistent with the approach to patient evaluation commonly employed in clinical practice. Two patient specific techniques which have been used to evaluate neck pain are the Problem Elicitation Technique and the Patient Specific Functional Scale. The disadvantage of this approach, particularly in research, is that without standardisation of content, the scale is different for each patient. The level of statistical correlation between patient specific scales and fixed-item questionnaires has been found to be only moderate.
Clinical studies in which multiple neck pain questionnaires are applied simultaneously in the same patient population have been identified as an important focus for research in this area. Specifically, patient specific questionnaires will help identifying the problems which are most common and relevant to specific sub-groups of patients with neck pain. This may assist the development or modification of fixed-item questionnaires, and enhance the psychometric evaluation, particularly the content and construct validity. Hoving et al. used the Problem Elicitation Technique to evaluate the validity of the Neck Disability Index and Northwick Park Neck Pain questionnaire in patients with neck pain associated with whiplash injury. They found that the two fixed item questionnaires did not fully cover the problems considered important in patients with whiplash injury, especially those concerning emotional and social functions. More recently, the Neck Disability Index has been shown to have poor construct validity and to be less responsive to change than the Patient Specific Functional Scale, in patients with cervical radiculopathy. Further, the Neck Disability Index has been shown to be less responsive to change than previously reported in patients with non traumatic neck pain. These findings suggest that analysis of the psychometric properties of the Neck Disability Index and other fixed item questionnaires in different groups of patients with neck pain should be an on-going process.
To date there has been little evaluation of the common problems associated with chronic, non traumatic neck pain, particularly in older patients. Recent studies of this patient group have examined patient variability and treatment dose, but an evaluation of the common functional problems and validity of fixed item questionnaires has not been conducted. The purpose of this study was to examine the content and construct validity of two fixed item questionnaires as measures of disability in patients with chronic, non traumatic neck pain. This was achieved through a comparison of the Neck Disability Index and Neck Pain and Disability Scale questionnaires in a cohort of patients with this disorder, and comparison of the responses to the fixed item questionnaires with a patient specific questionnaire, the Problem Elicitation Technique.
In the development of neck pain questionnaires, assumptions were made as to the nature of the functional limitations associated with neck pain. However, patient input is considered paramount in the development and evaluation of an outcome measure. While there was some input from patients in the construction of the Neck Disability Index and Neck Pain and Disability Scale, some questionnaires have been developed with little or no input from patients with neck pain. Establishing the validity of a questionnaire is important to ensure that it reflects the nature and spectrum of the problems experienced by the majority of patients. The validity of the Neck Disability Index and Neck Pain and Disability Scale has been investigated in patients with whiplash-related neck pain, but this is the first study to specifically examine the validity of two commonly used disability questionnaires in an older cohort of patients with chronic, non traumatic neck pain.
The Problem Elicitation Technique simulates clinical practice by asking patients to identify physical, emotional and cognitive problems specific to their neck pain disorder. It serves to elicit the problems specific to each patient, thereby reducing the ‘noise’ created when items not relevant to the patient are included. The most commonly reported functional problems in the present study were disturbed sleep, driving, and lifting, while frustration was the most common emotional problem. In patients with whiplash, who were significantly younger than the patients in the current study, the most common functional problems identified were work for wages, fatigue during the day, participation in sports, and driving, while the most common emotional problem was depression. Driving or riding in a car was the only common functional problem experienced by both patient groups. This finding suggests that the impact of neck pain on physical and emotional functions may be somewhat different in older patients with non traumatic neck pain compared to younger patients who have whiplash related neck pain. This is consistent with the studies which have reported differences in the nature and severity of physical impairments in patients with neck pain of traumatic origin, compared to those with a non-traumatic onset.
Of the 10 most common problems identified by the Problem Elicitation Technique, 6 were included in the Neck Disability Index and 7 were included in the Neck Pain and Disability Scale, which supports the content validity of both questionnaires for this patient population. Sleep disturbance, driving and frustration were ranked as the three most commonly reported problems. All are included in the Neck Pain and Disability Scale, while frustration is not addressed in the Neck Disability Index. A significant impact on psychological function has been described in patients with chronic, non-traumatic neck pain, which was found to improve with improvements in pain intensity and functional limitation. The Neck Pain and Disability Scale differs from the Neck Disability Index in that it includes questions which relate specifically to emotion and social function. The Neck Pain and Disability Scale uses sub domains to identify more specifically the areas of physical and psychological functions most commonly indicated by the patient as being affected. While most of the common functional problems relevant to this patient group are included in the Neck Disability Index and Neck Pain and Disability Scale, the greater scope of the latter questionnaire may provide better information about the impact of the disorder on the patient more broadly. The results of the present study suggest that neck pain questionnaires should have a greater emphasis on neck function, activities of daily living and psychological function, and limited emphasis on symptoms such as pain intensity, tissue tenderness and movement restrictions which can be measured in other ways.
The high correlation between the Neck Disability Index and Neck Pain and Disability Scale scores suggests that they measure the same construct in this patient group. While the questionnaire format and scoring systems are different, the questionnaires address a range of common items, which relate to function rather than symptoms. Previous studies have shown high correlation between the Neck Disability Index and other fixed-item neck pain questionnaires, where the items in the questionnaires were very similar. The only previous study to directly compare the Neck Disability Index and Neck Pain and Disability Scale found a moderate correlation between questionnaires, in younger patients with neck pain of both traumatic and atraumatic origins.
Consistent with the study of Hoving et al., there was a moderate correlation between the Problem Elicitation Technique and both fixed-item questionnaires, which suggests that the Problem Elicitation Technique measures a somewhat different construct. This may be due to the Problem Elicitation Technique only scoring items of relevance to each patient. For this reason, the Problem Elicitation Technique reflects clinical practice as it identifies problems relevant to the individual, which may include issues not addressed in fixed item questionnaires. A recommendation based on the results of the present study is that the Problem Elicitation Technique should be used in conjunction with a fixed-item questionnaire, as each provides different information about the study population. While fixed item questionnaires are relatively simple to administer, the Problem Elicitation Technique requires some training and experience of the interviewer to ensure consistency in its application and adherence to the target concept.
During the study the relevance of the driving item in the Neck Disability Index was raised by some patients, as many of the subjects did not drive, either due to their age or the neck pain disorder. The applicability of the driving item in the Neck Disability Index to non drivers has not previously been considered and may be an area for review. Previous studies have chosen to modify the Neck Disability Index in an attempt to improve the relevance of the questionnaire to the specific study population. In the present study, the item was answered by either a driver or a passenger, consistent with the driving question in the Neck Pain and Disability Scale. This modification to the Neck Disability Index should be considered if the questionnaire is used in future studies with this patient group.
A potential limitation of this study is the relatively small study population. However, the characteristics of the patients were consistent with those of larger studies of patients with chronic, non traumatic neck pain. The higher proportion of women in this study (65%) is consistent with gender ratios in other neck pain studies where the proportion of female subjects has been between 60 and 70%. The age and symptom duration suggest that degenerative pathology and the effects of aging may be important in the development of the symptoms, however, a review of radiological examinations and correlation with symptoms were not part of the present study. The patients in the study were receiving treatment in a public health system, and the problems identified may not reflect those of all patients with non traumatic neck pain in the broader community.
In conclusion, the Neck Disability Index and Neck Pain and Disability Scale both identified the common problems considered important by the patients, and the Neck Pain and Disability Scale included all problems ranked as most important. Both questionnaires have good content validity and are therefore equally relevant for use in this patient group. The broader scope of the Neck Pain and Disability Scale, particularly in relation to emotional and social functions, may be an advantage in future studies. In future research involving chronic, non traumatic neck pain, it is recommended that a patient specific questionnaire such as the Problem Elicitation Technique should be used in conjunction with a fixed item neck pain questionnaire, as each seems to measure a somewhat different construct.