Download Screening for Psychological Factors in Patients With Low

Screening for Psychological Factors in
Patients With Low Back Problems:
Waddell's Nonorganic Signs
or the majority of patients with low back pain (LBP), the cause of their
pain is unknown.' Psychological factors, which may include behavioral, cognitive, or somatoform components, can be just as important
as the diagnosis of pathology affecting the low back in a patient's
recovery from a low back p r ~ b l e r n . ~A- ~
recent US Agency for Health Care
Policy and Research clinical practice guideline recommends exploration of
psychological factors when an individual with an acute low back problem is
having difficulty regaining his or her tolerance to a~tivity.~
Feuerstein and Beattie5 discussed several biobehavioral instruments that can
be used to identify psychological factors in individuals with LBP. If factors are
identified that are potential contributors to the low back problem, the
physical therapist can then refer the patient to the appropriate professional.
Routine application of these instruments, however, may be impractical during
physical therapy examinations because of the time required for administration and scoring as well as the expertise needed to interpret the results. Thus,
there is a need for a brief screening tool to help identify patients who may
require more detailed psychological testing. A review of the description and
diagnosis of psychological disorders that may relate to LBP is beyond the
scope of this update. For further information on these areas, the reader is
referred
Signs of organic problems are findings from the physical examination that
indicate the presence of pathology or disease. Paresthesia over the lateral
border of the foot, for example, is a sign for S1 nerve root involvement. Signs
of nonorganic problems, in contrast, are findings that deviate from the usual
presentation of d i s e a ~ eBoth
. ~ organic and nonorganic signs may be present
in a patient with LBP. Therefore, the presence of nonorganic signs should not
be equated with malingering or the presence of a psychological problem, but
only with the need for further investigation.
Scalzitti DA. Screening for psychological factors in patients with low back problems: Waddell's nonorganic signs. Phys
Thm. 1997;77:306-312.1
Key Words: Assessment, Low back problems, Nonorganic signs, Psychosocial.
David A Scalzitti
306
Physical Therapy. Volume 77 . Number 3 . March 1997
The presence of
nonorganic signs
Waddell et aI8 described a group of signs that indicate
the presence of nonorganic problems for patients with
LBP. Waddell has also referred to these signs as "behavTesting for these
ioral signs" or "inappropriate ~igns."2.~
signs is performed as part of the physical examination
and takes less than 1 r n i n ~ t e Nonorganic
.~
signs have
been used to describe different characteristics of
patients with LBP. The purpose of this update is to
describe the use of Waddell's nonorganic signs as a
screening tool for psychological factors in patients with
LBP. Additionally, the relationship between the nonorganic signs and physical impairments, disability, and
treatment outcomes will be discussed.
Waddell's Nonorganic Signs
In the early 1900s, nonorganic signs were frequently
used to detect malingering in patients with LBP.lOJ1As
medical and psychological knowledge progressed, it
became clear that the diagnosis of malingering may have
been based on overly simplistic assumptions, and the use
of these nonorganic signs fell out of favor. The modern
use of nonorganic signs for patients with low back
problems increased greatly after 1980, when Waddell et
a18 grouped eight signs into five types. These five types,
or categories of signs, are tenderness, simulation, distraction, regional disturbances, and overreaction (Table).
Waddell and colleagues investigated 16 other signs,
including grip strength, lumbar sensory changes, and
pretibial tenderness, but did not include them in their
final battery because of poor intertester and intratester
reliability, overlap with other signs, and difficulty for the
examiner to learn.
According to Waddell et al,s a nonorganic sign (an
indication of a nonorganic contribution to a patient's
low back problem) observed during the physical exami-
should alert the
clinician to the
need for more
nation is scored as positive. If a sign is positive,
then that type of nonorganic sign is present.
One nonorganic sign in
comprehensive
isolation may be present
with some organic contesting.
ditions
and
should
therefore be discounted.
A sensory regional disturbance, for example, may be present in persons with
spinal stenosis with multiple nerve root involvement.
Waddell et als found that the presence of three or more
types of nonorganic signs correlated with the results of
psychological tests indicating problems. According to
Waddell et al, the presence of a single sign is not
associated with an indication of psychological problems.
The presence of three or more types of nonorganic signs
has been the most consistently used criterion for the
finding of a positive Waddell's nonorganic signs test,
although other methods have been proposed.12J3 Unless
otherwise specified in this update, therefore, a positive
test for nonorganic signs refers to finding the presence
of three or more types of nonorganic signs. A negative
nonorganic signs test is the finding of only one or two
types of signs, although a patient may have more than
three nonorganic signs because of multiple signs within
a specific type.
Reliability
Agreement was high (86%) for two examiners in detecting the presence of nonorganic signs in a group of 50
patients with chronic LBP.s Agreement between examinations in the same patients was 85%. (The mean length
of time between examinations was 23 days.) McCombe et
all4 reported poor intertester reliability between two
DA Scalzitti, PT, OCS, is Clinical Instructor, Department of Physical Therapy, University of Illinois at Chicago, 1919 W Taylor St (M/C 898),
Chicago, IL. 60612-7251 (USA) ([email protected]),and Specialist in Physical Therapy, Department of Physical Therapy, University of Illinois
Hospital, Chicago, IL 60612-7233. Address all correspondence to Mr Scalzitti at the first address.
Physical Therapy . Volume 77 . Number 3 . March 1997
Scalzitti
. 307
Table.
Waddell's Nonorganic Signsa
Type of
Nonorganic Sign
Nonorganic Sign
Description
Tenderness not related to a particular skeletal or neuromuscular structure; may be either
superficial or nonanatomic.
Tenderness
Superficial
The skin in the lumbar region is tender to light pinch over a wide area not associated
Nonanatornic
Deep tenderness, which is not localized to one structure, is felt over a wide area and
often extends to the thoracic spine, sacrum, or pelvis.
with the distribution of a posterior primary ramus.
These tests give the patient the impression that a particular examination is being carried
out when in fact it is not.
Simulation tests
Axial loading
Low back pain is reported when the examiner presses down on the top of the patient's
head; neck pain is common and should not be considered indicative of a nonorganic
sign.
Rotation
Back pain is reported when the shoulders and pelvis are passively rotated in the same
plane as the patient stands relaxed with the feet together; in the presence of root
irritation, leg pain may be produced and should not be considered indicative of a
nonorganic sign.
A positive physical finding is demonstrated in the routine manner, and this finding is then
Distraction tests
checked while the patient's attention is distracted; a nonorganic component may be
present if the finding disappears when the patient is distracted.
Straight leg raising
Dysfunction (eg, sensory, motor) involving a widespread region of body parts in a
manner that cannot be explained based on anatomy; care must be taken to distinguish
from multiple nerve root involvement.
Regional disturbances
Overreaction
The examiner lifts the patient's foot as when testing the plantar reflex in the sitting
position; a nonorganic component may be present if the leg is lifted higher than when
tested in the supine position.
Weakness
Demonstrated on testing by a partial cogwheel "giving way" of many muscle groups that
cannot be explained on a localized neurologic basis.
Sensory
Include diminished sensation to light touch, pinprick or other neurologic tests fitting a
"stocking" rather than a dermatomal pattern.
May take the form of disproportionate verbalization, facial expression, muscle tension
and tremor, collapsing, or sweating; judgments should be made with caution,
minimizing the examiner's own emotional reaction.
"Adapted from Waddell G, McCulloch J.4, Kurnmrl E, Venner RM. Nonorganic physical signs in low-back pain. Spine. 1980;5:117-125.
orthopedic surgeons and between a surgeon and a
physical therapist in detecting individual nonorganic
signs. Confidence intervals of Kappa coefficients
included zero for the nonorganic signs of tenderness
and regional disturbances, suggesting that agreement
was not better than chance. McCombe et al, however,
did not examine the reliability of the examiners in
determining the presence of three or more nonorganic
signs. This finding should caution clinicians regarding
the use of positive nonorganic signs in isolation.
The nonorganic sign of overreaction requires the clinician to make judgments based on observations of the
patient's behavior. The other signs are from tests conducted during routine examinations. The presence of
overreaction, therefore, may be more difficult to identify
than other nonorganic signs. Several methods and
instruments can be used to quantify observation of a
patient's behavior during the physical examination.15
308 . Scalzitti
Keefe and Block16 described a method for observing
overt pain behaviors to provide a means of identifying
the presence of guarding, bracing, rubbing, grimacing,
and sighing during a physical examination. Waddell and
Richardsong obtained a Pearson product-moment correlation coefficient of .65 when examining the relationship
between the nonorganic signs test and overt pain behaviors in 120 patients who had LBP for at least 3 months.
Measurements obtained with the UAB Pain Behavior
Rating Scale, which is one instrument for measuring
pain behavior, were also highly correlated ( r =.73) with
the results of the nonorganic signs test in 103 patients
with LBP.I7
Nonorganic Signs and Psychological Findings
In their original study of nonorganic
al-eported
a correlation between
nonorganic signs and scores on the
depression, and hysteria scales of the
signs, Waddell et
the presence of
hypochondriasis,
Minnesota Multi-
Physical Therapy . Volume 77 . Number 3
. March 1997
phasic Personality Inventory. These scales of the Minnesota Multiphasic Personality Inventory traditionally represent a measure of psychological distress in patients
with LBP. In addition, correlations have been found
between the presence of nonorganic signs and other
psychological instruments, including the disease affirmation and hypochondria1 disturbance scales of the Illness
Behavior Questionnaire (IBQ),IRthe Distress and Risk
Assessment Method (DR,4M),I9 and pain drawing^.^.^^
Waddell et alRcaution, however, that nonorganic signs
should not be overinterpreted and used as substitutes for
comprehensive psychological assessment. Instead, they
should be used as part of an examination to identify
patients who require more detailed testing.
with LBP who were seeing an orthopedist for the first
time showed three or more nonorganic signs. The
authors reported three or more nonorganic signs in 33%
of two different samples of patients with chronic LBP
a n d in 50% of a third sample of patients with chronic
LBP. The three samples of patients had all been off from
work for many months with a high incidence of previously failed treatments. No positive tests were detected
among subjects without LBP. Factors responsible for the
increased occurrence of nonorganic findings in patients
with chronic LBP have not been identified. The likelihood of finding three or more nonorganic signs may
increase with the duration of the problem or because of
the failed treatments.
The sensitivity and the specificity of eight psychometric
instruments, including Waddell's nonorganic signs test,*
for detecting psychological disturbances in patients with
LBP were determined in a group of 264 persons.I2
Results from each instrument were compared with a
"gold standard" of psychological disturbance, which was
defined as a positive response to three or more of the
eight psychometric tests. Specificity of the nonorganic
signs for correctly identifying patients who were nonpsychologically disturbed was 86% in men and 84% in
women. Sensitivity of the nonorganic signs for correctly
identifying patients who were psychologically disturbed
was 44% in men and 48% in women. This study
was limited, however, by the lack of a universal "gold
standard" of psychological disturbances with which to
compare the different instruments. In the study,
measurements with each instrument were compared
with a compilation of measurements obtained with
the other instruments. Correlations among the eight
instruments may not have been found if the instruments
were measuring different aspects of psychological
disturbances.
Nonorganic Signs and Tests of
Musculoskeletal Performance
Nonorganic contributions to a patient's LBP may coexist
with organic contributions. Organic findings may be
influenced by nonorganic factors, and in some patients,
nonorganic findings may be influenced by organic factors. Waddell et a122 evaluated the relationship between
the presence of the nonorganic signs and 27 tests of
musculoskeletal impairments in 120 patients with
chronic LBP. Reproduction of the patient's pain during
hip and knee movements and limitations in passive knee
flexion, hip flexion force, hip abduction force, and
prone isometric trunk extension were positive more
frequently in the patients who had two or more nonorganic signs (29%) than in the patients who had only
one or no nonorganic signs (71%). The only impairments not correlated with a nonorganic component
were those related to spinal posture and lumbar flexion.
Based on these findings, the authors concluded that the
physical tests of musculoskeletal impairments that they
investigated were better indicators of illness behavior
than of physical impairment.
Nonorganic Signs and Demographics
Age, gender, occupation, or compensation status d o not
appear to influence the results of the nonorganic signs
test.Wayes et al," however, found nonorganic signs
more frequently in patients with LBP who were anticipating or receiving financial compensation as compared
with those who were not anticipating or receiving compensation. In this study, however, other factors differed
between the two groups of patients. Thus, the role of the
nonorganic signs is difficult to assess.
Groups of patients with LBP with three or more nonorganic signs performed poorer on tests of force production, range of motion, and motor skills than did
groups of patients with LBP without nonorganic
signs.2"-'"hese
tests included tests of lumbar range of
motion and isometric force on an Isostation B-ZOOThf
lumbar dynamometert.2"24and tests of lifting, gripping,
and physical dexterity o n an ERGOSTMWork Simulator.x." Menard et a12Vound that patients with LBP with
nonorganic signs produced lower torques for isometric
elbow flexion and isometric knee extension than did
patients without nonorganic signs. The authors contended that musculoskeletal performance as measured
by dynamometers does not necessarily reflect maximum
physical capacity. Low values on any of these tests,
The length of time that a patient has had LBP appears to
increase the likelihood of finding a positive nonorganic
signs test. Waddell et alQeported that 12% of patients
'The seven othrr instrumenrs \+,err a pain drawing. the Slodified Somatic
Perception Questionnaire. the Hospital Anxiety Scale, the Hospital Depression
Scale, rhr Zung Depression Scale, the Illness Behavior Questionnaire. and a
nonorganic svmptoms test
Physical Therapy . Volume 77 . Number 3
. March 1997
Isotechnologies Inc, 328 Elizabeth Brady Rd. PO Box 1239, Hillsborough. NC
27278.
'Work Recovery Inc, 2341 S Friebus, Suite 14, Tucson, .42 85713.
Scalzitti
. 309
however, could not be used to identify individuals with
nonorganic problems, because some individuals with a
positive nonorganic signs test scored as well as some
individuals without nonorganic signs.
Cooke et a124 measured force and range of motion in
patients with chronic LBP, using a lumbar dynamometer. The same test was repeated after 4 weeks of an active
reconditioning exercise program. Patients with a positive
nonorganic signs test demonstrated improvements in
force that were greater than improvements that might be
expected as a result of physiologic changes or a learning
effect of the test procedure. The authors suggested that
the improved force generation might have been due to
alterations in illness behavior rather than to an improvement in physical capacity.
Findings that nonorganic components may contribute to
measures of musculoskeletal impairments suggest that
these measures, which are frequently used by physical
therapists for patients with LBP, may also reflect a
psychological component of disability. In addition, these
data suggest that physical therapists may want to continue measuring musculoskeletal impairments but need
to consider the influence of other factors, such as illness
behavior, on these tests. Likewise, benefits from treatment focused on physical reconditioning may result in
reducing disability by improving an individual's psychological status, and thus his or her tolerance to activity,
rather than just improvements in the measurement of
musculoskeletal impairments, such as peak torque of the
lumbar extensors.
patient's work status. A poor surgical outcome in this
study was defined as postsurgical episodes of disabling
back or leg pain, chronic use of narcotic medications,
further surgery, or inability to return to work. Relief
from pain and reduced disability depended on the
presence of an accurate diagnosis of a surgically treatable pathological condition without the presence of
nonorganic signs.
Outcomes of nonsurgical treatments of patients with
LBP have also been influenced by the presence of
nonorganic signs. Lehmann et also found that electroacupuncture treatment of patients with chronic LBP
who had three or more nonorganic signs was no more
effective for pain reduction than a sham treatment. In
contrast, the authors found that treatment of patients
with electroacupuncture, in the absence of nonorganic
signs, resulted in a greater decrease in pain than did the
sham treatments.
Patients with illness behavior as measured by the presence of nonorganic signs, nonorganic symptoms, and a
pain drawing received more treatments than did patients
who did not exhibit illness behavior in a study by
Waddell et al.31 These treatments included medication
use, lumbar injections, orthopedic supports, physical
therapy, spinal manipulation, and bed rest. Based on this
finding, a clinician should seriously consider whether
there is overutilization of treatments when patients who
test positive for nonorganic signs show no progress. For
these patients, treatment might be directed toward
addressing the illness behavior.
Relationship Between Nonorganic Signs and
Treatment Outcomes
Ability of Nonorganic Signs to Predict
Return to Work
Nonorganic phenomena can interact with expected
treatment outcomes in patients with LBP. Several investigators"-29 have described poorer results from lumbar
surgery in patients with nonorganic signs. McCull0ch2~
found that 97 of 109 patients with a nonorganic compe
nent who underwent chemonucleolysis continued to
have back or leg pain that prevented their return to full
activity. One hundred eighty-six of 327 patients without
nonorganic signs, in contrast, were free of pain or had
minimal limitations in activity following the chymopapain injection. Dzioba and DoxeyZ8found that only 49%
of patients with two or more nonorganic signs were
approved to return to work by a physician 12 months
after various forms of lumbar surgery, as compared with
78% of patients who had only one or no nonorganic
signs following surgery.
A common goal in the rehabilitation of workers with
LBP is to return them to work. There is conflicting
evidence about the ability to use nonorganic signs for
predicting return to work. Bradish et a132reported that a
positive nonorganic signs test at initial assessment in a
group of workers with a low back injury (N= 120) did not
correlate with work status between 12 and 18 months
after injury. In contrast, 0hlund et all7 found a relationship (r=.34) between nonorganic signs and the time
needed by a group of automobile workers (N=103) to
return to work. In this study, return to work was defined as
the return to the same job at least half-time.
In a prospective study by Waddell et al,Z9 psychological
factors, including the presence of a positive test for
nonorganic signs, correlated with a poor surgical outcome, as assessed by a physician, the patient, and the
3 10 . Scalzitti
, ~a~study of 134 patients with
Lancourt and K e t t e l h ~ tin
LBP, found that the nonorganic signs of axial loading,
simulated rotation, distraction, and a sensory regional
disturbance were among the factors that were better
predictors of return to work than were ankle and knee
reflexes, motor loss, and sensory loss in a dermatomal
pattern. This relationship was seen for patients who
returned to work within the first 6 months after injury
Physical Therapy
. Volume 77 . Number 3 . March 1997
but not for patients who were off work for greater than
6 months. Recently, KummelS4described two new nonorganic signs: lumbar pain during isolated cervical movement and lumbar pain limiting active shoulder movement. The presence of these two signs in addition to the
presence of three or more of Waddell's nonorganic signs
improved the ability to predict patients who failed to
return to work in this retrospective study of 717 patients.
The treatment received by injured workers may influence their return to work. Werneke et all3 evaluated a
physical conditioning program designed to meet each
patient's job requirement for 170 workers with LBP. One
hundred fifteen of the patients showed work status
improvement within 3 months of completing the program. At least one nonorganic sign was present in 47%
of the patients whose work status did not improve, as
compared with 12% of the patients who demonstrated
improvement. The number of nonorganic signs present
at discharge from the program was reduced for 82% of
the patients whose work status improved. In contrast to
the high su.ccess rate from physical conditioning, when
patients with nonorganic findings received treatments
described as "symptomatic and at the discretion of the
physician," less than 40% returned to work.92
Other factors, besides the presence of nonorganic signs,
may influence an injured worker returning to previous
job duties. Waddell et alZ9 found return to work after
lumbar surgery was predicted by physical, psychological,
and occupational factors. Physical therapists should consider the relationship of these factors in the treatment of
injured workers. The referral to an appropriate professional or multidisciplinary team should be made for
management of any confounding factors when a
patient's work tolerance fails to improve from physical
therapy.
as a malingerer does little to help the patient enhance
his or her tolerance for activity. Instead, the factors that
are limiting the patient from recovering his or her
tolerance for activity should be identified, and interventions should be targeted toward modification of the
limiting factom5
Classification of movement dysfunction in patients with
LBP may help clinicians to identify individuals who will
benefit from specific treatments. Failure to account for
the presence of nonorganic findings may lead to the
misclassification of patients, because nonorganic factors
may influence patients' performance on tests used to
classify them. Delitto et a135 screen for nonorganic signs
in their treatment-based classification scheme and suggest referral to an appropriate practitioner when screening is positive. Marras et alS6developed a classification
scheme for patients with low back disorders based on the
higher derivatives of trunk velocity. Using this method,
Marras et a1 found that patients with nonorganic findings were distinguishable from patients in nine other low
back disorder categories.
The utility of Waddell's nonorganic signs has been
described for patients with LBP. To date, nonorganic
signs tests for musculoskeletal problems in other regions
of the body are not commonly used. Development of
nonorganic signs tests for patients with other musculoskeletal problems may help to guide management of
these patients.
Nonorganic signs are found more frequently in persons
with chronic LBP as compared with persons with acute
LBP. Further investigation may reveal how nonorganic
behaviors increase and develop in patients with chronic
LBP. Treatment focused on prevention of the development of nonorganic signs may reduce the occurrence of
chronic LBP and back-related disability.
Clinical Implications
A physical problem may coexist with the presence of
nonorganic signs. Thus, the presence of nonorganic
signs does riot eliminate the need for a complete physical examination. A patient with a cauda equina syndrome, for example, may be classified as exhibiting
nonorganic behavior based on sensory and motor losses
and overreaction to the examination because of the
intensity of symptoms. Physical examination, however,
should identify the structural etiology of the problem,
and appropriate treatment should be directed toward
the pathological condition.
According to Waddell et al,8 nonorganic signs by themselves should not be equated with malingering or the
presence of a psychological problem. Rather, the finding
of nonorganic signs should alert the clinician to the
need for more comprehensive testing. Labeling a patient
Physical Therapy . Volume 77 . Number 3
. March 1997
Summary
The role of Waddell's nonorganic signs test as a screening tool for psychological factors in the examination of
patients with low back problems has been described. The
presence of nonorganic signs should alert the physical
therapist to the need for additional psychological tests
and should not necessarily be considered an indicator of
malingering. Nonorganic signs may coexist with organic
findings. An illness behavior role of the nonorganic signs
is suggested, as they have been related with disability in
addition to physical impairments. Physical therapy management for these patients should focus on treatment of
illness behavior and on combating disability.
Scalzitti . 3 1 1
Acknowledgments
I thank Louise J White, PT, and Pamela J Woodall, PT,
for their kind assistance with the preparation of this
update.
References
1 Spitzer WO. Diagnosis of the problem (the problem of diagnosis):
scientific approach to the assessment and management of activityrelated spinal disorders-a monograph for clinicians: report of the
Quebec Task Force on Spinal Disorders. Spine. 1987;12:S16-S21.
2 Waddell G, Main CJ, Morris EW, et al. Chronic low-back pain,
psychologic distress, and illness behavior. Spine. 1984;9:209-213.
3 Delitto A. Are measures of function and disability important in low
back care? Phys Ther. 1994;74:452-462.
4 Bigos S, Bowyer 0 , Braen G, et al. Acute Low Back Problems in Adults:
Clinical Practice Guideline No. 14. Rockville, Md: Agency for Health Care
Policy and Research, Public Health Service, US Department of Health
and Human Services; 1994. AHCPR publication 95-0642.
5 Feuerstein M, Beattie P. Biobehavioral factors affecting pain and
disability in low back pain: mechanisms and assessment. Phys Ther
1995;75:267-280.
6 Diagnostic and Statistical Manual of Mental Disorders. 4th ed. M'ashington, DC: American Psychiatric Association, 1994.
7 McCahill ME. Somatoform and related disorders: delivery of diagnosis as first step. Am Fam Physician. 1995;52:193-203.
8 Waddell G, McCulloch JA, Kummel E, Venner RM. Nonorganic
physical signs in low-back pain. Spine. 1980;5:117-125.
9 Waddell G, Richardson J. Observation of overt pain behaviour by
physicians during routine clinical examination of patients with low
back pain.] Psychosom Res. 1992;36:77-87.
10 Collie J. Malingering and Feigned Sickness. London, England: Edward
Arnold (Publishers) Ltd; 1913.
11 Hoover CF. A new sign for the detection of malingering and
functional paresis of the lower extremities. J A M . 1908;51:746-747.
12Greenough CG, Fraser RD. Comparison of eight psychometric
instruments in unselected patients with back pain. Spine. 1991;16:
1068-1074.
19 Main CJ, Wood PLR, Hollis S, et al. The Distress and Risk Assessment Method: a simple patient classification to identify distress and
evaluate the risk of poor outcome. Spine 1992;17:42-52.
20 Chan CW, Goldman S, Ilstrup DM, et al. The pain drawing and
Waddell's nonorganic physical signs in chronic low-back pain. Spine.
1993;18:1717-1722.
21 Hayes B, Solyom CAE, Wing PC, Berkowitz J. Use of psychometric
measures and nonorganic signs testing in detecting nomogenic disorders in low back pain patients. Spine 1993;18:1254-1262,
22 Waddell G, Somerville D, Henderson I, Newton M. Objective
clinical evaluation of physical impairment in chronic low back pain.
Spine. 1992;17:617-628.
23 Hirsch G, Beach G, Cooke C, et al. Relationship between performance o n lumbar dynamometry and Waddell score in a population
with low-back pain. Spine. 1991;16:1039-1043.
24 Cooke C, Menard MR, Beach GN, et al. Serial lumbar dynamometry
in low back pain. Spine. 1992;17:653-662.
25 Cooke C, Dusik LA, Menard MR, et al. Relationship of performance
on the ERGOS work simulator to illness behavior in a workers'
compensation population with low back versus limb injury. J Occup
Med. 1994;36:757-762.
26 Menard MR, Cooke C, Locke SR, et al. Pattern of performance in
workers with low back pain during a comprehensive motor performance evaluation. Spine. 1994;19:1359 -1 366.
27 McCulloch JA. Chemonucleolysis.] Bone Joint Surg [Br]. 1977;59:4552.
28 Dzioba RB, Doxey NC. A prospective investigation into the orthopaedic and psychologic predictors of outcome of first lumbar surgery
following industrial injury. Spine. 1984;9:614-623.
29 Waddell G, Morris EW, Di Paola MP, et al. A concept of illness
tested as an improved basis for surgical decisions in low-back disorders.
Spine. 1986;11:712-719.
30 Lehmann TR, Russell DW, Spratt KF. The impact of patients with
nonorganic physical findings on a controlled trial of transcutaneous
electrical nerve stimulation and electroacupuncture. Spine. 1983;8:
625-634.
31 Waddell G, Birchner M, Finlayson D, Main CJ. Symptoms and signs:
physical disease or illness behaviour? BMJ. 1984;289:739-741.
13 Werneke MW, Harris DE, Lichter RL. Clinical effectiveness of
behavioral signs for screening chronic low-back pain patients in a
work-oriented physical rehabilitation program. Spine. 1993;18:24122418.
32 Bradish CF, Lloyd GJ, Aldam CH, et al. Do nonorganic signs help to
predict the return to activity of patients with low-back pain? Spine.
1988;13:557-560.
14 McCombe PF,'~airbankJCT, Cockersole BC, Pynsent PB. Reproducibilit~of physical signs in low-back pain. Spine. 1989;14:908-918.
33 Lancourt J, Kettelhut M. Predicting return to work for lower back
pain patients receiving worker's compensation. Spine. 1992;17:629640.
15 Solomon PE. Measurement of pain behaviour. Physiotherapy Canada.
1996;48:52-58.
16 Keefe FJ, Block AR. Development of an observation method for
assessing pain behavior in chronic low back pain patients. Behau Ther.
1982;13:363-375.
17 0hlund C, Lindstrom I, Areskoug B, et al. Pain behavior in industrial subacute low back pain, part I: reliability-concurrent
and
predictive validity of pain behavior assessments. Pain. 1994;58:201-209.
34 Kummel BM. Nonorganic signs of significance in low back pain.
Spine. 1996;21:1077-1081.
35 Delitto A, Erhard RE, Boling RW. A treatment-based classification
approach to low back syndrome: identifying and staging patients for
conservative treatment. Phys Ther. 1995;75:470-489.
36 Marras WS, Parnianpour M, Ferguson SA, et al. The classification of
anatomic- and symptom-based low back disorders using motion measure models. Spine. 1995;20:2531-2546.
18 Waddell G, Pilowsky I, Bond IMR. Clinical assessment and interpretation of abnormal, illness behaviour in low back pain. Pain. 1989;39:
41-53.
Physical Therapy. Volume 7 7 . Number 3 . March 1997