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The Neck Disability Index - State of the Art 1991-2008

The Neck Disability Index - State of the Art 1991-2008 - Clinical Hub, UW Health Clinical Tool Search, UW Health Clinical Tool Search, Questionnaires, Related


STATE-OF-THE-ART PAPERS
THE NECK DISABILITY INDEX:ST
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respect to the “use of tablets” (ie, medication for pain or
Canadian Memorial Chiropractic College, 6100 Leslie St., Toronto,
sleep). This was deemed unsuitable because many subjects
might not be taking such medications. The wording of all the
Ontario, Canada M2H 3J1 (e-mail: hvernon@cmcc.ca).
Paper submitted March 27, 2008.
were more commonly used at that time.
The first phase in the development of the new instrument,
later deemed the Neck Disability Index (NDI), consisted of
refined. Drafts were submitted to patients and health
practitioners for feedback, resulting in further revisions to
the wording of the items. A pilot test was then launched
using 5 whiplash-injured patients. This resulted in unan-
imous rejection of the OI item “sex life,” which was replaced
by an item for ‘recreation.’ A final revision involved changes
to the wording of 2 of the original OI items: pain intensity
and sleep. In the original OI, these items were rated with
Professor, Canadian Memorial Chiropractic College, 6100 Leslie
St., Toronto, Ontario, Canada.
Submit requests for reprints to: Howard Vernon, DC, PhD,
0161-4754/$34
Copyright ' 20
doi:10.1016/j.jm
s of daily living.” The inclusion of this type
hed the OI and similar instruments from the
‘reading,’ and ‘work.’
Rating scales for these items were then developed and
of item distinguis
simpler measures
rpose. Most of the items in the OI could be regarded as
ecific “activitie
addition of 4 new items: ‘headaches,’‘concentration,’
Before 1991, no instrument was available to assess the
lf-rated disability of patients with neck pain. In the
evious decade, a few of such instruments for patients with
w back pain had been developed, chiefly, the Oswestry
w Back Pain Index (OI)
1
and the Roland-Morris Low
ck Pain Questionnaire.
2
Recognizing the deficiency with
spect to neck pain, Vernon undertook to develop a similar
strument suitable for patients with neck pain. It was
cided to model this instrument on the OI, so permission
m its primary author, J. Fairbanks, was obtained for that
appropriateness and retained if deemed applicable to pat
with neck pain. Six items were initially thought to
suitable: ‘pain intensity,’‘personal care,’‘lifting,’‘sle
‘driving,’ and ‘sex life.’ Descriptive studies on patients
neck pain experiencing chronic pain were reviewe
identify additional daily activities or health aspects repo
to be importantly affected in these patients. Informal sur
of patients and a small consulting team of health practitio
supplemented this search for items upon which neck
was considered to have a significant impact. The consu
team then provided consensus ratings that resulted in
ISTORY OF THE NECK DISABILITY INDEX item selection. First, items from the OI were reviewed
Spine; Cervical Vertebrae
Howard Vernon, DC, PhD
ABSTRACT
Background: Published in 1991, the Neck Disability Ind
disability in patients with neck pain. This article reviews
its psychometric properties—reliability, validity, and res
presented into its use in studies of the prognosis of whip
conservative therapies for neck pain.
Special Features: The NDI is a relatively short, paper
research settings. It has strong psychometric characteristi
of late 2007, it has been used in approximately 300 pub
endorsed for use by a number of clinical guidelines.
Summary: The NDI is the most widely used and most st
patients with neck pain. It has been used effectively in b
common problem. (J Manipulative Physiol Ther 2008;31
Key Indexing Terms: Neck Pain; Treatment Outcome
.00
08 by National University of Health Sciences.
pt.2008.08.006
ATE-OF-THE-ART, 1991-2008
x (NDI) was the first instrument designed to assess self-rated
e history of the NDI and the current state of the research into
nsiveness—as well as its translations. Focused reviews are
ash-injured patients as well as its use in clinical trials of
encil instrument that is easy to apply in both clinical and
and has proven to be highly responsive in clinical trials. As
cations; it has been translated into 22 languages, and it is
ngly validated instrument for assessing self-rated disability in
th clinical and research settings in the treatment of this very
491-502)
eliability and Validity; Outcome Assessment (Health Care);
detractors in these 2 items was then revised to reflect either
intensity, for pain, or duration, for sleep. This final version
491

Table 1. Systematic review of studies of the psychometric properties of the NDI
Author (first author) NP/WAD Sample Reliability Internal consistency Factor analysis Responsivity
Knapp [5] NP 46 0.91 at 1 d 0.81
Wallace [6] NP 38 12 wk ES = 1.35 (59% reduction)
Jette [7] ES = 0.75
Hains [8] NP 237 Item order has
no effect
0.92 1
Westaway [9] NP • c/w NDI and clinician's prediction
of change = 0.54
Riddle [10] NP 146 • Positive for change
• Equivalent to SF-36 Physical and
Mental scales for most issues
Stratford [11] NP 48 • MDC = 5
• MCIC = 5
Chok [12] NP 46 0.9 pre-post tx: z = −3.88,
P b .001
Ackelman [13] NP 59 2 d: 0.97 NDI c/w DRI = 0.95
3 wk: 0.95 NDI c/w SF-36 Phys = −0.88
3 mo: 0.94 NDI c/w VAS activity = 0.86
Modified NDI at
2 d: 0.97
NDI c/w VAS pain = 0.60
Wlodyka-Demaille [14] NP 101 0.93 at 1 d 0.93 at 1 d 2 factors
Hoving [15] WAD 71 c/w NDI and Problem Elucidation
Technique = 0.57
Bolton [16] NP 102 ES = 0.80/0.88
4-6 wk
Wlodyka-Demaille [17] NP 71 ES = 0.55
SRM = 0.55
c/w GPC = 0.48
Cook [18] NP 203 0.92 at 1 d; 0.74 1
0.48 at 7 d
Cleland [19] Cervical
radiculopathy
38 • MDC= 10.2
• MCID = 7.0
• Change in stable patients: r = 0.68
Lee [20] NP, controls 301 0.90 0.92 ES = 1.04;
SRM = 1.17
AUC re: GPE = 0.79
Baseline pats vs controls:
32.8 vs 9.1 P b .01
Vo s [21] WAD 187 0.90 at 1 wk • Responsiveness
Ratio = 1.82
• MDC = 1.66
McCarthy [22] NP 160 0.93 at 1-2 wk 0.86
492 Journal of Manipulative and Physiological TherapeuticsVernon
September 2008The Neck Disability Index

te
88
85
493VernonJournal of Manipulative and Physiological Therapeutics
The Neck Disability IndexVolume 31, Number 7
Mousavi [24] NP 30 0.90 0.
Pool [25] NP 183
Trouli [26] NP 65 0.93 (0.84;0.97) 0.
Table 1. (continued )
Author (first author) NP/WAD Sample Reliability In
Stewart [23] WAD 132
was submitted to the pilot group and was unanimously
endorsed as relevant and easy to use.
Since the original publication in 1991,
3
only 1 small
change has been made to the original English version,
namely, the addition of the qualifier “neck” was added in all
places where the sole term “pain” hadbeenpresent,
clarifying that the detractor was concerned with the patient's
“neck pain” (items 1, 2, and 3).
SCORING AND INTERPRETATION
Each item is scored out of 5 for a maximum total score of
50. Care should be taken in reporting the score as either out of
50 or as a percentage out of 100.Most studies have reported the
scores out of 50. Several strategies for dealing with missing
data or noncompliance with an item have been developed.
When only 1 item is missing, some authors have scored the
NP indicates neck pain; ES, effect size; c/w, correlated with; DRI, Disability R
patient evaluation; pats, patients; GROC, global rating of change; GPC, globa
Fig 1. Translations of the NDI available on the MAPI Web site
(www.proqolid.com).
• English for Australia
• English for the United States
• English for the UK
• Danish
• Dutch
• Finnish
• French
• French Canadian
• French for Switzerland
• German
• German for Switzerland
• Italian
• Italian for Switzerland
• Norwegian
• Polish
• Portuguese
• Spanish for Spain
• Spanish for the US
NDI out of 45 and converted the score to a percentage. When
several items are missing, some authors have used the mean
value of the scored items and inserted this into the missing
items. If 3 or more items are missing, the overall score may be
suspect and, especially in research studies, may be invalid.
The scoring interpretation for the NDI is slightly different
than for the OI, as follows: 0-4 = none; 5-14 = mild; 15-24 =
moderate; 25-34 = severe; over 34 = complete. These 5
categories have been revised by several authors in
subsequent studies, especially in the effort to determine a
dichotomous cutoff for “disabled” vs “not disabled” or
“recovered” vs “not recovered” (see below).
rnal consistency Factor analysis Responsivity
• 6 wk: ES = 0.77,
• Improved = 0.95,
• SRM = 0.91,
• Improved = 1.16;
• AUC c/w GPE = 0.76
• c/w SF-36
• c/w pain VAS = 0.71
• MDC = 10.5
• AUC = 3.5


= preferred method
1 factor: • MDC = 1.78
EV = 4.48 • SEM = 0.64
Var. = 44.8% • c/w GROC = 0.30
ating Index; tx, treatment; SRM, standardized response mean; GPE, global
l perceived change; EV, eigenvalue; Var, variance.
THE ORIGINAL 1991 REPORT
The original study reported on test-retest reliability over
a 2-day period, obtaining a value of 0.89 (P b .05). Internal
consistency was measured using Cronbach α, with a total
index value of .80. The highest scoring items (average out
of 5) were the following: headaches = 2.6; lifting = 2.2;
recreation = 2.2; reading = 2.1; and driving = 2.0. The total
index scores of the study sample were normally distributed,
as follows: 0 to 4 (none) = 2%; 5 to 14 (mild) = 35%; 15 to
24 (moderate) = 48%; 25 to 34 (severe) = 15%; and greater
than 35 (complete) = none. The convergent validity was
assessed by comparing the NDI scores to the scores of
the McGill Pain Questionnaire (MPQ)
4
: NDI/MPQ total
score = 0.70; NDI/MPQ-number of words = 0.69. The
responsiveness of the NDI was assessed by comparing, in a
small group of patients who have whiplash undergoing
chiropractic treatment, the change in NDI scores over 3
weeks to a Visual Analogue Scale (VAS) for “pain
improvement” at 3 weeks. These scores were moderately
strongly correlated (0.60). The average change in NDI score
was 33.2%; the average VAS improvement score was 56%.

Table 2. Studies of prognosis in WAD using the NDI
Author (first author) Sample size Baseline NDI Follow-up time(s) Results
Atherton [39] 480 N/A 1, 3, and 12 mo 1. NDI N 19 was 1 of only 5 factors in a multivariate model
predicting persistent pain
2. Relative risk ratios
NDI
0-14 = 1.0
15-22 = 1.6 (0.99-2.5)
N22 = 2.8 (1.8-4.2)
Sterling [40] 65 6 mo = 17.67 (16.5) 2-3 y 1. NDI N 30 c/w:
24-36 mo = 15 (14.1) Hi autonomic measures
Hi TSK
Hi GHQ-28
- hi IES
2. Odds ratio for persistent pain at 2-3 y
NDI N 30 = 1.0-1.1 (ss)
3. Predictive model of
Initial NDI score
Age
Cold pain threshold
IES score
explained 56% of variability of follow-up NDI scores
For moderate/severe group (at follow-up) this model
had an 84.6% accuracy
4. Low initial NDI significantly predicted likelihood of
recovery (only variable)
5. NDI is a better predictor of outcome than pain score alone
Crouch [41] 170 N/A 4-6 wk 1. At 4 wk (according to NDI score)
No disability = 37%
Mild disability = 37.6%
Moderate = 21.2%
Severe = 4.1%
2. Variables correlated to NDI score
Seatbelt use = 0.038
x-ray obtained = 0.004
Midline tenderness = 0.008
Saw a GP = 0.001
Sterling [42] 76 34.15 (2.4) 6 mo 1. Significant corr. with NDI at follow-up
High initial NDI
Cold hyperalgesia
Older age
Acute stress
Bunketorp [43] WAD =108 N/A 17 years 1. Persistent neck pain @ 17 yrs:
CON = 931 WAD = 55%
CON = 29%, P = .001
NDI scores at 17 y:
WAD = 22 (21.7)
CON = 10.6 (15.2), P = .001
Lankester [44] 277 N/A 9 mo-5 y 1. NDI score corr. with:
GHQ = 0.58 (P b .01)
Gargan/Bannister Scale = 0.72 (P b .01)
Joslin [45] 85 1. NDI score is corr. with litigation status (P = .000)
Sterling (from 2003
paper) [46]
76 6 mo 1. NDI score corr. with recovery categories:
a. Recovered = b8
b. Mild disab. = 10-28
c. Mod/severe = N30
494 Journal of Manipulative and Physiological TherapeuticsVernon
September 2008The Neck Disability Index

up time(s) Results
1. NDI scores at 24 wk:
a. Recovered = 14.2 (4.6-25.4)
b. Persistent pain = 27.9 (15.4-40). P b .000
2. Cutoff for recovery = b15
3. Initial NDI score predicted recovery status at 53%
4. Addition of TSK score predicted a further 29% = 83.3%
1. Recovery cutoff = 20
2. Univariate OR for NDI N20 to predict
non-recovery = 7.4 (P b .05)
3. Multivariate analysis = only NDI score signif.
(P b .05) predicted poor outcome: OR = 11.2
1. NDI scores used to create recovery categories:
a. Recovered = 38%
b. Mild disab. = 39%
c. Mod/Severe = 23%
495VernonJournal of Manipulative and Physiological Therapeutics
The Neck Disability IndexVolume 31, Number 7
Table 2. (continued )
Author (first author) Sample size Baseline NDI Follow-
Nederhand [47] 82 24.4 (7.1) 24 wk
Miettinen [48] 144 3 years
Sterling [49] 76 6 mo
METHODS
The search strategy for the current report for articles
using or referring to the NDI was conducted as a citation
search of the 1991 publication using Science Citation
Index, through the Scholar's Portal Web of Science.
Articles were retrieved from 1991 to December 2007.
Articles were reviewed to insure that the instrument used in
assessing the self-rating of disability by patients with neck
pain was actually the NDI. This resulted in 287 qualified
citations. These articles were then classified according to
the following categories: psychometric studies, diagnosis,
prognosis, treatment designs (clinical trials, case series, and
case studies), treatment type (surgical, conservative,
injections), patients with whiplash, patients experiencing
chronic pain, translation studies, and systematic reviews/
practice guidelines.
Various subsets of articles on specific topics have been
reviewed systematically by conducting quality reviews (see
2. At 1 mo, all groups had signs of hypersensitivity.
At 6 mo., only Mod/severe group showed these signs.
So: Hi NDI scores c/w persisting hypersensitivity
Sterling [50] 66 3 mo 1. NDI scores used to create recovery categories:
a. Recovered = 38%
b. Mild disab. = 33%
c. Mod/Severe = 29%
2. At 1 mo, all groups had signs of hi EMG, lo JPE.
At 3 mo., only Mod/severe group showed
So: Hi NDI scores c/w persisting motor dysfunction
Bunketorp [51] 108 17 y 1. Recovered vs persisting pain NDI: 8.5 (16) vs
32 (20), P = .000
2. NDI scores c/w radiating arm pain: r = 0.61
Moog [52] 43 22.4 6 mo NDI score NOT c/w:
litigation status
presence of vibration-induced pain
N/A indicates not applicable; c/w, correlated with; TSK, Tampa Scale for Kinesiophobia; GHQ-28, Global Health Questionnaire-28; IES, Impact of Events
Scale; ss, statistically significant; disab., disability; GP, general practitioner; corr., correlation; CON, control patient; Mod., moderate; OR, odds ratio; JPE,
joint position error; EMG, electromyography.
Table 3. Cutoff or category values for the NDI
Study Findings
Atherton et al
[39], 2006
• NDI N 18: 1 of only 5 factors in a multivariate
model predicting persistent pain at 1 and 3 and
12 mo.
• relative risk ( RR) for persisting pain:
▪ 0-14 = 1.0
▪ 15-22 = 1.6 (0.99;2.5)
▪ N22 = 2.8 (1.8;4.2)
Sterling et al
[40], 2003-2005
• Established recovery categories:
▪ Recovered = b4
▪ Mild disability = 5-14
▪ Moderate/Severe disability = N15
Nederhand
et al [47], 2004
At 24 wk, cutoff value of 15 (0-14 vs 15N) strongly
correlates with outcome
Miettinen
et al [48], 2004
At 24 wk cutoff value of 20 strongly correlates with
outcome

ea
th
F
4
7
4
2
2
Van Schalkwyk -B [66] 15 50 SMT (cont.) 27.7 53 4
6
6
ea
496 Journal of Manipulative and Physiological TherapeuticsVernon
September 2008The Neck Disability Index
Wood -A [67] 15 50 SMT (instr.) 33
Wood-B [67] 15 50 SMT 40
QS indicates quality score; Tx, treatment; M, male; F, female; T1, T2, T3, m
Table 4. RCTs of manipulation + NDI (high quality)
Author (first name/group) n QS Tx Age % M
Bronfort-A [56] 64 89 SMT + low tech exer 45 41
Bronfort-B [56] 64 89 SMT + sham elec 44.3 42
Evans-A [57] 64 89 SMT + rehab exer 45 41
Evans-B [57] 64 89 SMT + sham elec 44.3 42
Giles-A [58] 35 84 SMT 39 51
Hurwitz-A [59,60] 171 74 SMT ± heat 46 32
Hurwitz-A [59,60] 171 71 SMT ± elec 46 32
Cleland-A [61] 19 68 SMT (thor) 36 26
Cleland-B [61] 17 68 SMT (sham thor) 35 26
Muller-A [62] 23 58 SMT 39 48
Giles-B [63] 20 58 SMT 42.5 53
QS indicates quality score; Tx, treatment; M, male; F, female; T1, T2, T3, m
manipulative therapy; tech, technical; exer, exercise; elec, electrical therapy;
Table 5. RCTs of manipulation + NDI (low quality)
Author (first name) n QS Tx Age M
Cilliers-A [64] 15 50 SMT (super. seg) 33 53
Cilliers-B [64] 15 50 SMT (both segs) 29.3 27
Parkin-Smith -A [65] 13 47 SMT (cerv) 33.8 54
Parkin-Smith-B [65] 17 47 SMT (cerv and thor) 37 71
Van Schalwyk-A [66] 15 50 SMT (ipsil.) 33.1 80
below for details for each category) and then extracting the
relevant data, summarizing these into evidence tables.
DISCUSSION
Psychometric Properties
Since 1991, 22 additional publications have reported on the
psychometric properties of the NDI.
5-26
Eight of these were
published before 2002
5-12
and most of these were included in
the only systematic review to date.
27
In that review, it was
acknowledged that (1) the NDI was the most widely used of
the several scales for self-rating disability in patients with neck
pain, which had been developed since 1991, and (2) the NDI
was the most well-validated of these instruments. Table 1
displays the results of 21 studies with original data on the
psychometric properties of the NDI up to 2007.
With regard to reliability, 8 studies in addition to the
original paper have reported test-retest correlations between
0.90 and 0.93.
5,12,14,18,20,21,22,24,26
Hains et al
8
reported that
item order did not affect the responses. The internal
consistency has been reported in 7 additional studies, with
Cronbach α values ranging from .74 to .93.
5,14,18,20,22,24,26
Four studies have calculated the factor structure of the
NDI,
8,14,18,26
with 3 agreeing that only 1 factor—physical
disability—is present. The reliability, internal consistency,
and factor structure of the NDI are now considered to be well
described in the literature and to be of very high quality.
superior segment; segs, segments; cerv, cervical; ipsil., ipsilateral; cont., contr
manipulative therapy.
% F T1 SD T2 SD ch ES T3 SD ch ES
59 26.4 8.5 18.6 9.2 7.8 0.89 14.1 8.7 12.3 1.43
58 27.8 10.3 20.2 11.5 7.6 0.70 15.8 12.3 12.0 1.06
59 26.3 8.4 15.5 10.5 10.8 1.4 15.6 11.8 10.7 1.06
58 27.9 10.2 19.5 12.9 8.4 0.72 20.5 13.5 7.4 0.65
49 26 16, 42 17 0, 36 9.0
68 13.1 6.2 10.0
68 13.1 6.2
74 28.4 11.9
74 33.6 14.2
52 28 18, 44 20 8, 40 8.0
47 32 22 18, 28 10.0
n scores at times 1, 2, and 3; ch, change scores; ES, effect size; SMT, spinal
or, thoracic spine.
1 SD 2 SD ch ES 3 SD ch ES
7
3
6 18.2 9.7 6.9 8.1 11.4
9 17.6 8.2 4.7 5.7 12.9
0 22.5 8.1 6 5.7 16.5 6.0 6.8 16.5
7 16.4 15.9 6.13 18.4 10.3 6.13 8 10.3
7 31.8 14.1 13.5 11.0 18.3
0 26.8 13.3 11.0 9.8 15.8
n scores at times 1, 2, and 3; ch, change scores; ES, effect size; super. seg.,
With regard to responsiveness, the minimum detectable
change (MDC) reported in 2 studies of patients with neck
pain is less than 2 points (out of 50, b4%),
21,26
although
Pool et al
25
reported an MDC of 10.4 points. Cleland et
al
19
reported on a small sample of patients with cervical
radiculopathy finding a much larger MDC; however,
because the NDI was not specifically designed for use in
this clinical group, these findings do not reflect on the NDI
in usual use. The minimum clinically important difference
or change (MCID/C) has been reported in 3 studies.
11,19,25
Stratford et al
11
determined an MDC and MCIC of 5 (5/
50) points by comparing NDI change scores with a
physician-rated change scale. Cleland et al
19
reported an
MCID of 10 points in the small sample of radiculopathy
patients. This clinical problem is generally more refractive
to treatment, so a larger MCID is not surprising. Pool et
al's
25
value of the area under the curve (AUC) comparing
NDI change vs global perceived change was 3.5 points.
This was deemed by these authors to be the more
appropriate value for MCIC.
Effect sizes, standardized response means and respon-
siveness ratios have been reported by 7 studies, with the
findings ranging from 0.80 to 1.82, all of which are large by
usual standards.
28
These studies report on variable treat-
ments over variable times and doses. The data on treatment
studies reviewed below is more precise for the effect sizes for
different treatment approaches.
alateral; instr., instrumented manipulation; thor, thoracic spine; SMT, spinal

6.8 7.5 7.2 6.4 0.91 7.4 5.9 6.5 1.02
6
7
1
4
1
1
an sc
enzie
497VernonJournal of Manipulative and Physiological Therapeutics
The Neck Disability IndexVolume 31, Number 7
Table 6. RCTs of exercise + NDI
Author (first name) n QS Tx Age M F 1
Bronfort-A [56] 63 89 Hi Int MedX 43.6 40 60 26.7
Evans-B [57] 63 89 Hi Int MedX 43.6 40 60 26.4
Hoving-B [68] 59 84 Active exer 45.9 30 70 13.9
Kjellman-A [69] 20 68 Active exer 46.8 20 80 16.5
Kjellman-B [69] 25 68 McKen 45.4 28 72 15
Ylinen-B [70] 59 82 Endur 46 0 100 22
Ylinen-C [70] 60 82 Streng 45 0 100 21
Hoving-B [71] 59 89 Active exer 45.9 30 70 13.9
Nikander-A [72] 60 82 Streng 45 0 100 17.5
Nikander-B [72] 58 82 Endur 45 0 100 19
Ylinen-A [73] 59 82 Streng 46 0 100 22
Kietrys-A [74] 72 61 Active exer 41.2 22 78 5.1
Ylinen-A [75] 57 84 Endur 46 0 100 20
Ylinen-B [75] 59 84 Streng 45 0 100 22
QS indicates quality score; Tx, treatment; M, male; F, female; T1, T2, T3, me
intensity; MedX, brand of exercise equipment; exer, exercise; McKen, McK
The NDI change scores correlate well with measures of
global change, with r values ranging from 0.30 to 0.76.
9,20,23,26
Finally, the NDI has been employed in numerous studies
of other instruments designed to evaluate patients with neck
pain. In the following list, the NDI was used as one of the
primary measures for determining the construct validity of
these new instruments. As all of these studies reported
acceptably high correlation coefficients, these studies
provide evidence for the convergent validity of the NDI
with other instruments whose purpose is more or less
equivalent (the reference cited is the first one to use the
NDI for comparison):
• The Copenhagen Neck Functional Disability Scale
(Jordan et al
29
)
• The Patient-Specific Scale (Neck) (Riddle and Stratford
10
)
• The Neck Pain and Disability Scale (Wheeler et al
30
)
• The Functional Rating Index (Feise et al
31
)
• The Aberdeen Back Scale (Neck) (Williams et al
32
)
Tra
ND
Po
tra
of
ar
of
m
an
Table 7. RCTs of mobilization + NDI
Author (first name) n QS Tx Age M F
Hoving-A [68] 60 84 Mobs 44.6 43 57
Hurwitz-B [60] 165 71 Mobs w/w.o heat 46 30 70
Korthals de Bos-A [76] 60 79 Mobs 44.6 43 57
Hurwitz-B [59] 165 74 Mobs w/w.o elec 46 30 70
Hoving-A [71] 60 89 Mobs 44.6 43 57
QS indicates quality score; Tx, treatment; M, male; F, female; T1, T2, T3, mea
mobilization; w/w.o, with or without; elec, electrical therapy.
Table 8. RCTs of physiotherapy + NDI
Author (first name) n QS Tx Age M F 1
Korthals de Bos-B [76] 59 79 Physio 45.9 30 70
Gustavsson-B [77] 16 71 Physio (indiv) 36 6 94 14
QS indicates quality score; Tx, treatment; M, male; F, female; T1, T2, T3, mean
physiotherapy; indiv, indivualized.
.5
6, 30 19 17, 22 3 13 10, 16 9
.4 4.6 3.6 .52 0.13
6, 28 14 6, 20 6 14 6, 20 6
6, 26 14 6,20 8 12 4, 22 10
ores at times 1, 2, and 3; ch, change scores; ES, effect size; Hi, high; int,
protocol; endur, endurance; streng, strength.
SD 2 SD Ch ES 3 SD ch ES
10.4 17.1 10.3 9.6 0.93 12.4 9.9 14.3 1.42
10.2 15 11.6 11.4 1.05 16.6 12.4 9.8 0.87
6.8 7.9 7.9 6 0.81
8 10.5 8 6 0.75 8.5 8.5 8 0.98
6 8 6 7 1.17 7.5 6 7.5 1.25
16, 28 14 11, 16 8
16, 26 12 10, 14 9
• The Cervical Spine Outcomes Questionnaire (BenD-
ebba et al
33
)
• The Bournemouth Questionnaire—Neck (Bolton et al
34
)
• TheWhiplash-Specific Disability measure (Pinfold et al
35
)
• The Core Outcomes for Neck Pain (White et al
36
)
• The Whiplash Disability Questionnaire (Willis et al
37
)
• The NHANES-ADL (neck) (Cook et al
38
)
nslations
As of late 2007, there were 6 published translations of the
I into French,
14
Dutch,
15
Swedish,
13
Korean,
20
Brazilian
rtuguese,
18
and Iranian.
24
In addition to these published
nslations, the author has worked with the MAPI Company
France to produce the numerous translations (Fig 1) that
e available at the MAPI website (www.proqolid.com). All
the MAPI translations were conducted using standardized
ethodologies of linguistic validation, including forward
d backward translations by linguistic experts, pilot testing
1 SD 2 SD ch ES 3 SD ch ES
13.6 7 5.8 5.8
13.3 6.3
7.5 7.2
13.3 6.3
13.6 7 6.4 6.9 6.4 6.1 7.2
n scores at times 1, 2, and 3; ch, change scores; ES, effect size; mobs,
SD 2 SD ch ES 3 SD ch ES
8 6.3
10, 24 14.5 8, 20 −0.5 14 6.8, 23 0
scores at times 1, 2, and 3; ch, change scores; ES, effect size; physio,

4.2
ean
QS, quality score; Tx, treatment; M, male; F, female; T1, T2, T3, mean score
m
498 Journal of Manipulative and Physiological TherapeuticsVernon
September 2008The Neck Disability Index
with clinicians and nonexperts in multiple iterations, final
confirmation by the original author, and standard formatting
and proof-reading. No separate psychometric studies were
Table 11. RCT of cervical pillow + NDI
Author (first name) n QS Tx Age M F 1
Erfanian-A [80] 14 55 Pillow 34.1 14 86 1
QS indicates quality score; Tx, treatment; M, male; F, female; T1, T2, T3, m
adv, advice.
Table 10. RCTs of medication + NDI
Author (first name) n QS Tx Age M F
Hoving-C [68] 64 84 Meds + adv 45.9 44 56
Giles-C [58] 40 84 Meds 39 58 42
Korthals de Bos-C [76] 64 79 Meds + adv 45.9 28 72
Muller-C [62] 19 89 Meds 39 58 42
Hoving-C [71] 64 89 Meds + adv 45.9 44 56
acupuncture; wash, washout period.
Table 9. RCTs of acupuncture + NDI
Author (first name) N QS Tx Age M F
Zhu-A [78] 14 80 Acup + Wash + Sham 50 64 36
Giles-B [58] 34 84 Acup 37.5 56 44
White-A [79] 70 89 Acup 53.9 34 66
Muller-B [62] 20 89 Acup 38 55 45
QS indicates quality score; Tx, treatment; M, male; F, female; T1, T2, T3,
conducted by the MAPI group on any of these translations.
Overlap exists between the separate French and Dutch
studies
14,15
which did conduct psychometric testing in their
respective languages.
As of December 2007, 2 other translations involving the
author are in preparation: Greek
26
and Gujarati (personal
communication, Sabapathy, 2007).
Clinical Guidelines
The NDI is explicitly endorsed as the instrument of choice
in the following guidelines for the treatment of whiplash-
associated disorder (WAD):
1. NHS Library:
- Clinical Knowledge Summaries
- Prodigy Guidelines
http://www.cks.library.nhs.uk/neck_pain
2. TransportAccidentCommission, Victoria State,Australia
http://www.tac.vic.gov.au/jsp/corporate/homepage/
home.jsp
3. New South Wales Motor Accidents Authority, Guide-
lines for the Management of Acute Whiplash-Asso-
ciated Disorders, 2nd Edition, 2007.
https://www.cebp.nl/media/m393.pdf
4. Clinical Practice Guidelines for the Physiotherapy
treatment of Patients with Whiplash-Associated Dis-
Wh
th
pr
or
Sa
ex
ac
ac
su
pr
sc
in
da
(3
de
(m
m
orders. Leigh et al, 2004. British Columbia Physiother-
apy Association
http://www.bcphysio.org/pdfs/wad.pdf
SD 2 SD ch ES 3 SD ch ES
7.8 14 7.1 0.18 11.9 5.5 3.1
scores at times 1, 2, and 3; ch, change scores; ES, effect size.
1 SD 2 SD ch ES 3 SD ch ES
15.9 7.1 10 7.2 5.6
23 16, 27 21 10, 25 5
7.4 8.5
21 6, 25 18 8,25 3
15.9 7.1 9.4 8.8 6.5
s at times 1, 2, and 3; ch, change scores; ES, effect size; meds, medication;
1 SD 2 SD ch ES 3 SD ch ES
10.2 4.7 6 4.5 4.2 0.91 6.1 4.8 4.1 0.85
18 10, 25 14 7, 21 8
16.8 6.34 11.8 6.59 5.06 0.79 10.9 6.27 5.82 0.92
18 11, 25 12 0, 16 12
ean scores at times 1, 2, and 3; ch, change scores; ES, effect size; Acup,
5. Clinical Practice Guidelines for Physical Therapy in
Patients with Whiplash-Associated Disorders. Bekker-
ing et al, 2003, Royal Dutch Society for Physical
Therapists.
http://www.ifomt.org/pdf/Guidelines/WhiplashGln.pdf
iplash-Associated Disorder: Prognosis Studies Using the NDI
There have been 41 studies involving patients with WAD
at have used the NDI. Seventeen of these involved the
ognosis of patients with whiplash, 14 of which reported
iginal data.
39-52
These studies were rated according to
ckett et al.
53
Studies rated in categories 3-5/5 were
cluded. The quality of these studies ranged from 2b-2c
cording to the classification by Sackett et al (all were
ceptable for inclusion). Data retrieval included numbers of
bjects, baseline NDI scores, follow-up NDI scores,
ognostic indicators, and where applicable, correlation
ores between NDI and other variables.
The groups within these reports were classified accord-
g to categories by Cote et al,
54
as follows: source of
ta—emergency department (n = 11), general practice
), insurance database (2), population study (1); study
sign—univariate (9), multivariate (7), or explanatory
odeling) (1).
The median follow-up time in these studies was 6
onths (1-204 months) (Table 2). The mean (SD) sample

1
1
e
4
e
499VernonJournal of Manipulative and Physiological Therapeutics
The Neck Disability IndexVolume 31, Number 7
Table 14. Change scores (/50) for various treatment modalities
Treatment (n) Mean change SD SEM
Manipulation:
NDI 2 (9) 8.8 1.2 .39
NDI 3 (4) 10.6 1.1 2.2
Exercise:
NDI (12) 7.8 3.8 1.09
NDI 3 (8) 10.8 3.8 1.36
Mobilization
Table 13. RCT of relaxation therapy + NDI
Author (first name) n QS Tx Age M F
Gustavsson-A [77] 13 71 Relaxation 43 0 100
QS indicates quality score; Tx, treatment; M, male; F, female; T1, T2, T3, m
Table 12. RCT of laser + NDI
Author (first name) n QS Tx Age M F
Dundar-A [81] 32 29 Low-level laser 40.8 16 8
QS indicates quality score; Tx, treatment; M, male; F, female; T1, T2, T3, m
size was 137 (120). One case control study
51
included
931 controls. Several recovery categorizations were
reported, all of which correlated with the original NDI
categories (Table 3). Recovery cutoffs range from 10-20/
50, with the average being 15/50. Odds or relative risk
ratios for high initial NDI and poor recovery were
reported from 1.1 to 11.2. Several predictive models
including high initial NDI scores were reported, account-
ing for up to 84.6% of variability in recovery status.
Several studies reported that NDI score was the best
predictor of outcome: low initial NDI predicts recovery;
high initial NDI recovery predicts chronicity.
The NDI has been shown to be highly useful in the
prognostication of outcome after WAD injury either alone or
within multivariable models. The NDI appears better than
‘pain level’ as a measure of symptom/disability status for
prognostic purposes. High NDI scores (N15/50) at 3 to 36
months postaccident are strongly correlated with several
important measures of physiologic dysfunction and physical
impairment, indicating that psychosocial and accident-
related factors are not the only correlates of high self-rated
disability in patients who have chronic WAD and that
attention to pathophysiologic factors such as muscular
dysfunction and central sensitization is warranted.
NDI 2 (3) 7.4
Acupuncture
NDI 2 (5) 7.05 3.1 1.38
Medication
NDI 2 (6) 5.02 3.1 1.39
The NDI in Random Clinical Trials (RCTs) of Conservative Treatment
In nonsurgical treatment studies, treatment groups were
classified as follows: manipulation, mobilization, physiother-
apy, exercise, acupuncture, medication, cervical pillow, laser,
and relaxation therapy. Each trial report was rated for quality
by 2 raters using the Maastricht-Amsterdam Rating Scale,
55
which gives a score out of 19. Studies attaining a score of
50% or more were considered of high quality.
Tables 4 to 13 display data on the different groups reported
in trials of conservative treatments for neck pain,
56-83
which
employed the NDI as an outcomemeasure (no. of groups N no.
of trials). Table 14 shows the mean (SD) and the SEM of
change scores at various intervals postbaseline for several of
these treatment modalities.
This review has only focused on those treatment studies
that have used the NDI; the purpose was not to conduct a
systematic review of all RCTs of conservative treatments
for neck pain. The primary purpose of this review was to
describe (not systematically analyze) the responsiveness of
the NDI as an outcome measure in these trials. The mean
changes obtained in the categories shown in Table 14 all
exceed the MCIC reported by Stratford et al,
11
although the
groups receiving medications appear to improve the least.
These mean changes range from 5 to 10 points or from 10%
to 20%. By way of interpreting these changes, Farrar et al
82
have reviewed the change scores on the 11-point pain scale
in 10 clinical trials for a variety of chronic pain complaints
(2724 subjects) and have determined that a 2-point or 20
SD 2 SD ch ES 3 SD ch ES
7 9, 25 15 7, 22 2 14 10, 22.5 3
an scores at times 1, 2, and 3; ch, change scores; ES, effect size.
1 SD 2 SD ch ES 3 SD ch ES
14.7 6.1 9.4 5.5 5.3
an scores at times 1, 2, and 3; ch, change scores; ES, effect size.
out of 100 mm change (20%) is clinically relevant for
chronic pain patients.
It could be argued that these change scores represent the
natural history of chronic neck pain or the placebo effect
within a trial and therefore do not reflect the influence of the
treatments provided. Vernon et al
83
investigated the average
change in pain scores in a separate group of controlled
clinical trials of conservative treatments for chronic neck pain
and found that these are not generally greater than 15mm on a
100-mmVAS (around 15% improvement). In several of these
studies, there was no change at all in pain scores in the control
groups over up to 10 weeks posttreatment. Considering the
findings of Farrar et al
82
and Vernon et al
83
with respect to
changes in pain scores of patients with chronic pain, the

oswestry low back pain disability index. Physiotherapy
1980;66:271-3.
and scoring methods. Pain 1975;1:275-99.
500 Journal of Manipulative and Physiological TherapeuticsVernon
September 2008The Neck Disability Index
5. Knapp S, Langworthy J, Breen AC. The use of the Neck
Disability Index in the evaluation of acute and chronic neck
pain. Proc. 12th Intern Conf Spinal Manip, Palm Springs, CA.
Boston (Mass): Foundation for Chiropractic Education and
Research; 1994. p. 10.
2. Roland M, Morris R. A study of the natural history of low back
pain. Part I. Development of a reliable and sensitive measure of
disability in low back pain. Spine 1983;8:141-4.
3. Vernon H, Mior S. The Neck Disability Index: a study of
reliability and validity. J Manip Physiol Ther 1991;14:409-15.
4. Melzack R. The McGill Pain Questionnaire: major properties
changes in disability/NDI scores obtained in this descriptive
review would appear to exceed what could be ascribed to
either the natural history or the placebo effect.
Other Treatment Modalities
The NDI has been used as a primary outcome measure in
57 surgical trials and 3 trials of injection-type therapies
(references available from author on request).
CONCLUSION
The current “state-of-the-art” of the NDI has been
reviewed here. The NDI is the oldest and most widely
used instrument for self-reporting of disability due to neck
pain. Its internal psychometric properties have been well
established in numerous cultural groups with neck pain: it is
highly reliable, strongly internally consistent, and with a 1-
factor structure for “physical disability.” It has strong and
well-documented convergent and divergent validity with
other instruments used in the evaluation of patients and
subjects with neck pain. Clinicians can confidently apply a
“minimum clinically important change” value of 3 to 5
points in their practice settings,
11
whereas researchers can
make use, in future clinical trials, of the large number of
reports of the responsiveness of the instrument to various
therapies over various time frames and according to various
indices of responsiveness.
The NDI has been translated into 22 languages, with 6
published reports and 1 large Web-based resource with 18
readily available versions. It has been used in 52 surgical
clinical trials and 3 trials of injection therapies as well as
RCTs of numerous conservative therapies, chiefly manipula-
tion and exercise. In this regard, it has served to expand the
range of outcome measurements of neck pain patients
beyond the limited use of pain scales and has enriched the
yield of these clinical trials.
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