Responsiveness of the Cervical Northern American Spine
Society Questionnaire (NASS) and the Short Form
36 (SF-36) in Chronic Whiplash

This section is compiled by Frank M. Painter, D.C.
Send all comments or additions to:    Frankp@chiro.org

FROM:   Clin Rehabil. 2012 (Feb); 26 (2): 142–151

Felix Angst, Martin L Verra, Susanne Lehmann, Françoise Gysi,
Thomas Benz, André Aeschlimann

Research Department,
Rehabilitation Clinic 'RehaClinic' Zurzach,
Bad Zurzach, Switzerland.

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Clinical messages The NASS was consistently less responsive in function than the SF-36 and cannot be recommended as a specific instrument to measure pain and function more responsively than the SF-36 in chronic whiplash disorder. The SF-36 seems to be a powerful, responsive instrument in chronic pain.

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Objective:   To determine and compare the sensitivity to change of the condition-specific cervical Northern American Spine Society (NASS) and the generic Short Form 36 (SF-36).

Design:   Prospective cohort study.

Subjects:   One hundred and seventy five patients after whiplash injury.

Interventions:   Four-week inpatient interdisciplinary pain management programme.

Main measures, analysis:   Responsiveness of the NASS and the SF-36 was quantified by effect size and standardized response mean and compared within the same construct by the modified Jacknife test. Ability to detect improvement was compared using sensitivities determined from receiver operating characteristics curves.

Results:   In pain, the NASS was comparable responsive to the SF-36 at the one-month follow-up (n = 175): effect sizes: 0.62 (NASS) versus 0.61 (SF-36), P = 0.914. The NASS was less responsive than the SF-36 in function: 0.23 versus 0.63, P < 0.001 and in pain+function: 0.35 versus 0.58 (P = 0.001). These relationships remained consistent using standardized response means, at the six-month follow-up (n = 103), and in the comparison of the sensitivities. Sensitivities at one month, pain: 70% (NASS) versus 62% (SF-36), P = 0.234; function: 65% versus 80%, P = 0.002; pain+function: 68% versus 78%, P = 0.035. The six-month data were similar.

Conclusions:   The generic SF-36 was more responsive in function and equally responsive in pain when compared to the condition-specific NASS. The SF-36 can be recommended as a responsive instrument for measurement of pain and function in chronic whiplash syndrome.

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From the FULL TEXT Article:

Introduction

Whiplash injury causes a complex paindominated syndrome in some victims of accidents leading to high demands on therapy management and costs per case. [1] Whiplash-associated pain syndrome has consequences in all aspects of biopsycho- social health and quality of life and comprehensive assessment is required. [2, 3] As in various chronic pain conditions, improvements due to treatment or in the natural course are often small and, by that, difficult to detect and to quantify. Condition-specific assessment instruments are expected to be more specific and thus more sensitive to measure small changes than generic, comprehensively measuring ones. [4] Sensitivity to measure change over time, synonymous responsiveness, is a major property of an instrument and an important part of its validity. [5] It is further a key criteria for outcome instruments established by the quality classification process of the Outcome Measures in Rheumatology Clinical Trials (OMERACT) carried out by World Health Organization (WHO), the American College of Rheumatology (ACR), and the European League Against Rheumatism (EULAR). [6]

Comparative data about responsiveness are often lacking when instruments’ properties and qualities are rated and compared. [7] This is especially true for instruments assessing neck pain syndromes. [7] The most often used specific instruments for neck pain syndromes are the Whiplash Disability Questionnaire (WDQ), the Neck Pain and Disability Scale (NPDS), the Oswestry Disability Index, cervical module (ODI), the Roland-Morris Questionnaire (RMQ), and the cervical version of the Northern American Spine Society questionnaire (NASS). [7]

When our interdisciplinary rehabilitation programme started in 2003, only the NASS had been translated and cross-culturally adapted into German: Whiplash Disability Questionnaire: not yet translated, Neck Pain and Disability Scale: translated in 2008, [8] Oswestry Disability Index, cervical module translated in 2006 [9], Roland-Morris Questionnaire: only the low back pain version translated in 1999. [10] While there are data about reliability, validity and effects of the NASS, [11-15] responsiveness of the NASS has not been compared to other instruments, especially, not by statistical tests. [14, 15] Furthermore, responsiveness of the NASS was not examined in the separated constructs of pain and function up to date. [14, 15] The need for testing the responsiveness of the NASS in non-surgical settings has especially been stated.7 The Short Form 36 (SF-36) is the most widely accepted and most frequently used generic instrument, also for comparative studies of responsiveness.

This prospective cohort study aimed to determine and compare the responsiveness of the NASS and the SF-36 in patients who underwent a specific interdisciplinary rehabilitation programme for chronic pain syndrome after whiplash injury. It was hypothesized that the conditionspecific NASS was more responsive than the generic SF-36.

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Discussion

We examined the ability of the NASS and the SF- 36 self-assessment outcome instruments to sensitively measure changes in pain and function in chronic whiplash patients after a four-week inpatient interdisciplinary pain management program (n = 175) and at six-months’ follow-up (n = 103). Both instruments were similarly responsive in pain. In function, and by that in most comparisons in pain+function, the SF-36 was the significantly more responsive tool.

The results were consistent over two measurement time points and over two analyses, the comparison of the responsiveness measures (effect sizes and standardized response means), and the sensitivity analysis by receiver operating characteristics curves. The relatively low to moderate correlations of the score changes between the NASS and the SF-36 confirmed the difficulties in the ability to detect score change over time of the two instruments. The observed score changes were higher than so-called minimal important differences, an estimate for an effect which patients (on average) perceive as subjective change (that is, by that, clinically important), on the SF-36 but not on the NASS. In summary, the NASS was not able to detect higher score changes over time in clinical outcome assessment of chronic whiplash when the SF-36 already was in the set of instruments.

The hypothesis that a condition-specific instrument – the NASS – is more responsive than a generic one – the SF-36 – could not be confirmed in this condition. One explanation for this may be that the extensive, detailed explications of the item level responses of the NASS may be too complicated for certain users in contrast to the short and simple ones of the SF-36. This may cause uncertainties in the response and blur effects. Secondly, overall functionality in the activities of daily living, particularly ambulation, may be more important than neck pain dependent tasks in chronic whiplash in contrast to acute neck pain.

The findings of this study stay in line with those of other studies.After three to four weeks comprehensive rehabilitation in cervical spine disorders, the effect size of SF-36 pain was 0.9 versus 0.54 of NASS pain+function in 42 inpatients and 1.31 versus 0.96 in 98 outpatients. [14] Effect data of SF- 36 function scales were not reported and statistical comparison of effect sizes between the NASS and the SF-36 was not performed. [14, 15] The pain+function score correlated with 0.70 to 0.80 to the SF-36 physical functioning, 0.28 to 0.65 to SF-36 bodily pain, and 0.56 to the SF-36 physical component summary score showingmoderate (for pain also small) construct overlap. [12, 14, 15] A second study about a rehabilitation programme with physiotherapy and spa pool therapy of 92 cervical pain patients reported effect sizes in SF-36 pain of 0.64 and SF-36 function of 0.32 while the effect size of the NASS pain+function was 0.55. [15] In 273 chronic soft tissue and back pain patients, the SF-36 showed similar responsiveness (bodily pain: effect size = 0.72) when compared to the pain numeric rating scale (effect size = 0.62) and to the pain severity scale of the Multidimensional Pain Inventory (MPI) (effect size = 0.85, all differences not significant). [25] One may thus hypothesize that the SF-36 is generally as responsive as condition- specific tools for pain in chronic (back) pain.

Astrength of the present study is the large, prospective cohort of subjects with consistent characteristics treated by a standardized therapy programme. The SF-36 and the NASS are well known worldwide, valid, profoundly tested selfassessment instruments and permit standardized measurement and comparison between cohorts of different conditions, countries, and cultures. To our knowledge, this is the first study which compared the effects/score changes of both instruments in the separated constructs of pain and function.

The following limitations have to be taken into account. To further examine the score changes in relation to minimal clinically important differences, a retrospective global health rating, the so-called transition question would have to be applied in addition.30 A second limitation arises from the fact that newer, more widespread instruments as the Whiplash Disability Questionnaire, and so on, have not been used because data collection for the present study started before the publication of their German versions. Further, the high drop-out rate of 41% between the onemonth and the six-month follow-up may be a limitation when comparing effects between groups but less when comparing effects within subjects. In the outcome paper, post-hoc analysis of the drop-outs detected low possible bias caused by the high rate of dropped-out subjects. [16] Finally, acute neck pain may result in different responsiveness findings than chronic neck pain and newer neck-specific instruments may be more responsive than both examined tools.

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