A New Evaluation Method for
Lumbar Spinal Instability:
Passive Lumbar Extension Test

Background and Purpose. Although many studies have described clinical
examination measures for the diagnosis of lumbar spinal instability, few of
them have investigated the sensitivity and specificity of the measures that were
used. The authors devised a passive lumbar extension (PLE) test for assessing
lumbar spinal instability. The purpose of this study was to investigate the
sensitivity, specificity, and positive likelihood ratio of this test. Subjects and
Methods. The PLE test as well as the instability catch sign, painful catch sign,
and apprehension sign tests were done for 122 subjects with lumbar degen-
erative diseases. The subjects were divided into 2 groups—instability positive
and instability negative— on the basis of findings on flexion-extension films of
the lumbar spine. The sensitivity, specificity, predictive values, and positive
likelihood ratio of each test were investigated. Results. The sensitivity and
specificity of the PLE test were 84.2% and 90.4%, respectively. These values
were higher than those of other signs. The positive likelihood ratio of the PLE
test was 8.84 (95% confidence interval

⫽4.51–17.33). Discussion and Conclu-

sion. The PLE test is an effective method for examining patients for lumbar
spinal instability and can be performed easily in an outpatient clinic. [Kasai Y,
Morishita K, Kawakita E, et al. A new evaluation method for lumbar spinal
instability: passive lumbar extension test. Phys Ther. 2006;86:1661–1667.]

Key Words: Functional radiographs, Lumbar degenerative diseases, Lumbar spine, Physical examinations,

Segmental instability.

Yuichi Kasai, Koichiro Morishita, Eiji Kawakita, Tetsushi Kondo, Atsumasa Uchida

Physical Therapy . Volume 86 . Number 12 . December 2006

1661

Research

Report

䢇

ўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўў

ўўўўўў

ўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўўў

L

umbar spinal instability is defined as the loss of
ability of the spine to maintain its pattern of
displacement under physiologic loads with no
initial or additional neurological deficit, no

major deformity, and no incapacitating pain.

1

At

present, lumbar spinal instability is diagnosed on the
basis of findings on flexion-extension films obtained by
lateral lumbar radiography, but there is no consensus
regarding the diagnostic radiographic criteria, and the
clinical definition of lumbar spinal instability is ambigu-
ous.

2– 4

Although many studies

5–10

have described clinical

examination measures for the diagnosis of lumbar spinal
instability, few of them

9,10

have investigated the sensitiv-

ity and specificity of the measures that were used. Among
those few studies, Abbott et al

9

reported a passive

accessory intervertebral motion test with a sensitivity of
29% and a specificity of 89% and a flexion passive
physiological intervertebral motion test with a sensitivity
of 5% and a specificity of 99.5% for the diagnosis of
translational lumbar spinal instability. These studies
showed that there are no clinical examination measures
for assessing lumbar spinal instability with both high
sensitivity and high specificity. In this study, we investi-
gated the sensitivity, specificity, and positive likelihood
ratio of a newly devised passive lumbar extension (PLE)
test originating principally from prone instability tests
reported by Wadsworth et al

11

and Magee.

12

Method

Subjects
The subjects enrolled in this study were 122 consecutive
patients who visited the spine clinic of our hospital
between January and June 2001 and who were diagnosed
as having lumbar spinal canal stenosis (89 patients; 27
patients had the central type, 15 had the lateral type, and
47 had both lateral and central types), lumbar spon-

dylolisthesis (21 patients), or lumbar degenerative scoli-
osis (12 patients). The subjects, 43 men and 79 women,
had a mean age of 68.9 years (range

⫽39–88 years) at

the time of the initial consultation. The duration of
illness was between 1 month and 5 years (X

⫽11.2

months). The mean Japanese Orthopedic Association
( JOA) score (perfect score

⫽29 points), which was devel-

oped to clinically assess the efficacy of treatment for
lumbar spine diseases, was 22.6 points (range

⫽5–29

points). The assessment items of the JOA scoring system
evaluated in the interview and clinical examination are
pain, gait disturbance, sensory disturbance, muscular
power, activities of daily living, and bladder function.
Eighty-six patients (70.5%) had lumbago, 74 (60.7%)
had intermittent claudication, and 52 (42.6%) had neu-
rological symptoms in the lower legs. Many of our
patients are referred to us by other clinics for further
evaluation and surgical treatment; of the 122 patients
enrolled in this study, 45 (36.9%) underwent spinal
decompression and fusion within 1 year after the initial
visit.

Radiological Evaluation of Lumbar Spinal Instability
Several radiographic diagnostic criteria have been pro-
posed for lumbar spinal instability

13–16

; however, at

present, there is no consensus in this regard. Therefore,
we reviewed the literature to check the cutoff values for
angular motion and translational motion used in the
evaluation of lumbar spinal instability. The reported
cutoff values for angular motion were 10 degrees
(Dupuis et al

2

), 15 degrees (White and Panjabi

1

and

Nachemson

4

), and 20 degrees (Hayes et al

17

); we

adopted the highest cutoff value, 20 degrees, for angular
motion. The reported cutoff values for translational
motion were 3 mm (Dvorak et al

18

and Knutsson

19

),

4 mm (Dupuis et al

2

), and 5 mm (Shaffer et al

15

and

Hayes et al

17

); we used the highest cutoff value, 5 mm,

Y Kasai, MD, is Associate Professor, Department of Orthopaedic Surgery, Mie University Graduate School of Medicine, Tsu City, Mie Prefecture,
Japan. Address all correspondence to Dr Kasai at: [e-mail].

K Morishita, MD, is Spine Surgery Fellow, Department of Orthopaedic Surgery, Mie University Graduate School of Medicine.

E Kawakita, MD, is Spine Surgery Fellow, Department of Orthopaedic Surgery, Mie University Graduate School of Medicine.

T Kondo, MD, is Spine Surgery Fellow, Department of Orthopaedic Surgery, Mie University Graduate School of Medicine.

A Uchida, MD, is Professor and Chairman, Department of Orthopaedic Surgery, Mie University Graduate School of Medicine.

Dr Kasai provided concept/idea/research design and writing. Dr Kawakita and Dr Kondo provided data collection, and Dr Morishita provided data
analysis. Dr Uchida provided project management.

An oral presentation of the results of this study was made at the 19th Annual Meeting of the North American Spine Society; October 25–30, 2004;
Chicago, Ill.

This article was received September 5, 2005, and was accepted August 7, 2006.

DOI: 10.2522/ptj.20050281

1662 . Kasai et al

Physical Therapy . Volume 86 . Number 12 . December 2006

for this parameter. With respect to angular motion,
Maigne et al

10

reported that patients showing an inter-

vertebral end-plate angle of less than

⫺5 degrees on the

flexion film had significant clinical symptoms relevant to
lumbar spinal instability; therefore, we also adopted a
cutoff value of

⫺5 degrees for the intervertebral end-

plate angle on the flexion film. Thus, we used the
following 3 criteria to assess radiological instability of the
lumbar spine: angular motion of 20 degrees, transla-
tional motion of 5 mm, and intervertebral end-plate
angle on the flexion film of

⫺5 degrees. We have no

evidence justifying the use of these 3 criteria for the
assessment of radiological instability of the lumbar spine;
however, because the cutoff values adopted for the
criteria are the highest among those previously reported,
we believe that they constitute a valid method. For
practical reasons, we distributed subjects who met 1 or
more of the 3 criteria into the lumbar spinal instability-
positive group and subjects who did not meet any of
those criteria into the lumbar spinal instability-negative
group.

The relationship between 2 vertebrae was assessed on
radiographic films for every lumbar vertebra from L1–2
to L5–S1 by 2 independent observers who were orthope-
dists and had 8 and 14 years of clinical experience. With
regard to the measurement methods, the end-plate angle
(Fig. 1) was defined as the angle generated by 1 line
drawn from the inferior margin of the superior vertebral
body and another line drawn from the superior margin
of the inferior vertebral body; angular motion was defined
as the difference between the end-plate angle obtained
from the extension film and that obtained from the
flexion film. Translation was calculated according to the

method of Stokes and Frymoyer

20

; the distance between

the 2 arrows shown in Figure 2 was measured, the
end-plate angle was obtained from 2 lines drawn from
the posterior margins of the superior and inferior verte-
bral bodies, and then the end-plate angle bisector was
drawn. The difference between the values measured by
the 2 observers was 0.3

⫾0.2 mm (X⫾SD) for transla-

tional motion, showing little measurement deviation
between the observers and very few errors introduced by
magnification. The differences between the values mea-
sured by the 2 observers were 1.2

⫾0.6 degrees (X⫾SD)

for angle motion, 0.3

⫾0.2 mm (X⫾SD) for translational

motion, and 0.2

⫾0.1 mm (X⫾SD) for the intervertebral

end-plate angle on the flexion film, showing little mea-
surement deviation between the observers. Eventually,
the radiographic assessments of lumbar spinal instability
by the 2 physicians coincided for all 122 subjects, reveal-
ing a concordance rate of 100%.

The evaluation based on these criteria revealed that 38
subjects were instability positive and 84 subjects were
instability negative, as shown in Table 1. There were no
significant differences between the 2 groups with regard
to age, sex, diagnosis, JOA score, or the numbers of
subjects who had been surgically treated.

PLE Test
In the PLE test (Fig. 3) that we have devised, the subject
is in the prone position; both lower extremities then are
elevated concurrently to a height of about 30 cm from
the bed while maintaining the knees extended and
gently pulling the legs. The PLE test was implemented by
2 independent orthopedists who had 12 and 15 years of
clinical experience. The physicians were unaware of the

Figure 1.

The end-plate angle was defined as the angle generated by 1 line
drawn from the inferior margin of the superior vertebral body and
another line drawn from the superior margin of the inferior vertebral
body.

Figure 2.

Translation was calculated according to the method of Stokes and
Frymoyer

20

; the distance between the 2 arrows was measured, the

end-plate angle was obtained from 2 lines drawn from the posterior
margins of the superior and inferior vertebral bodies, and then the
end-plate angle bisector was drawn.

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results of the radiological assessment of lumbar spinal
instability. We surmised that hypermobility derived from
lumbar spinal instability would cause low back pain and
that because the PLE test was associated with severe
hypermobility of the lumbar region, it would induce low
back pain. The lumbar region was judged to be abnor-
mal when, during elevation of both lower legs during the
PLE test, the subjects complained of strong pain in the
lumbar region, including “low back pain,” “very heavy
feeling on the low back,” and “feeling as if the low back
was coming off,” and such pain disappeared when they
returned the lower legs to the initial position. In con-
trast, subjects’ complaints of an abnormal sensation,
such as mild numbness or a prickling sensation, during
this test was not considered abnormal. Because initially
the judgment of a positive result (complaint of pain in
the lumbar region) was thought to be ambiguous in the
PLE test, the test was conducted twice to examine the
reproducibility and reliability. The test was repeated 2 to
4 weeks after the first test for the convenience of a
follow-up visit. If the subjects complained of strong pain
or any abnormal sensation in the lumbar region during
the second PLE test, like they did during the initial visit,
then they were judged to have positive PLE test results. If
the results were evaluated as abnormal in 1 of the 2 PLE
tests, either at the initial or at the second visit, then the
subjects were judged to have equivocal PLE test results. If

no abnormality was detected in either test, then the
subjects were judged to have negative PLE test results.

Instability Catch Sign, Painful Catch Sign, and
Apprehension Sign Tests
The instability catch sign, painful catch sign, and appre-
hension sign tests were performed by an orthopedist
who had 20 years of clinical experience and who had not
implemented the PLE test. These 3 tests were done prior
to the PLE test. The PLE test and the other 3 tests for
lumbar spinal instability were assessed by different phy-
sicians because assessments may be influenced by pre-
conceived ideas if these tests are assessed by same
physician. In addition, the tester for these 3 tests also was
unaware of the results of the radiological evaluation of
lumbar spinal instability. These 3 tests for lumbar spinal
instability were described in detail by Kotilainen and
Valtonen.

5

For the instability catch sign test, subjects

were asked to bend their bodies forward as much as
possible and then return to the erect position; subjects
who were not able to return to the erect position because
of sudden low back pain were judged to have lumbar
spinal instability. For the painful catch sign test, subjects
were asked to lift both lower legs in the knee extension
position and then return their legs slowly to the exami-
nation table; subjects whose legs fell down instantly to
the examination table because of sudden low back pain
were judged to have lumbar spinal instability. For the
apprehension sign test, subjects were asked whether they
had felt a sensation of lumbar collapse because of
sudden low back pain when they performed ordinary
acts, including bending back and forth or from side to
side and sitting down or standing up; subjects who had
experienced such a sensation were judged to have
lumbar spinal instability. As for other tests, there are no
publications reporting the sensitivity and specificity of
these 3 clinical examinations for assessing lumbar spinal
instability. Because these 3 tests are commonly used in
clinical practice to assess lumbar spinal instability at our
clinic, we investigated their sensitivity and specificity and
compared the results with those of the PLE test.

Table 1.

Clinical Data for Lumbar Spinal Instability-Positive and Lumbar Spinal Instability-Negative Groups

a

Parameter

Lumbar Spinal Instability-Positive
Group (n

ⴝ38)

Lumbar Spinal Instability-Negative
Group (n

ⴝ84)

Age, y, X

⫾SD

68.3

⫾12.3

69.1

⫾10.5

Sex

9 men and 29 women

34 men and 50 women

Diagnosis (no. of subjects)

LSCS (26), LS (8), LDS (4)

LSCS (63), LS (13), LDS (8)

JOA score, points, X

⫾SD

20.8

⫾7.3

23.6

⫾9.6

No. (%) of surgically treated subjects

18 (47.4)

27 (32.1)

a

Diagnosis: LSCS

⫽lumbar spinal canal stenosis, LS⫽lumbar spondylolisthesis, LDS⫽lumbar degenerative scoliosis. JOA⫽Japanese Orthopedic Association.

Figure 3.

Passive lumbar extension test.

1664 . Kasai et al

Physical Therapy . Volume 86 . Number 12 . December 2006

Data Analysis
The numbers of subjects who had positive results in the
PLE test or the 3 clinical tests for lumbar spinal instabil-
ity in the instability-positive and instability-negative
groups were determined. The sensitivity, specificity, pos-
itive and negative predictive values, and positive likeli-
hood ratios of the PLE test and the 3 clinical tests for
lumbar spinal instability also were determined. For the
data analysis, we created a 2

⫻ 2 table from the data

obtained and calculated sensitivity, specificity, preva-
lence, positive predictive value, and negative predictive
value. The positive likelihood ratio was calculated with
the following formula: sensitivity/(1

⫺ specificity). The

95% confidence interval of the natural logarithm of the
positive likelihood ratio was calculated with the follow-
ing formula: standard deviation of natural logarithm of
the positive likelihood ratio

⫾ natural logarithm of the

positive likelihood ratio.

Results

PLE Test
Of the 38 subjects in the lumbar spinal instability-
positive group, 32 had positive PLE test results and 6 had
negative results (Tab. 2). Of the 84 subjects in the
lumbar spinal instability-negative group, 8 had positive
PLE test results and 76 had negative results. No subjects
had equivocal results, for instance, normal results in the
first evaluation and abnormal results in the second
evaluation. Table 3 shows the sensitivity, specificity,
positive and negative predictive values, and likelihood
ratio of the PLE test.

Instability Catch Sign, Painful Catch Sign, and
Apprehension Sign Tests
Table 2 shows the numbers of subjects who had positive
or negative results in the 3 clinical tests for lumbar spinal
instability. The sensitivity, specificity, predictive values,
and positive likelihood ratio of the PLE test were higher
than those of the instability catch sign, painful catch
sign, and apprehension sign tests, as shown in Table 3.

Discussion
The results of this study revealed that as a test for
evaluating lumbar spinal instability, the PLE test was
more sensitive and specific than the instability catch
sign, painful catch sign, and apprehension sign tests. For
the PLE test, we believe that the judgment was valid
because contradictory results, such as a positive assess-
ment in the first test and a negative assessment in the
second test, were not obtained, and the results were
assessed similarly. Thus, this test was considered to be
highly reproducible.

Many of the subjects with positive PLE test results were
women, probably because many of the subjects with
lumbar spondylolisthesis were women, many of whom
were lumbar spinal instability positive. The results of the
PLE test did not correlate with those of the JOA score
and the presence or absence of neurological symptoms
and intermittent limping. Because low back pain proba-
bly is attributable to lumbar spinal instability in subjects
with positive PLE test results, the data from the PLE test
for subjects with lumbar degenerative diseases can be
very useful for determining treatment strategy, that is,
whether to provide conservative treatment with a corset
or to perform procedures such as spinal fusion and

Table 2.

Data from Passive Lumbar Extension (PLE) Test and Instability Catch Sign, Painful Catch Sign, and Apprehension Sign Tests

Group

No. of Subjects With Indicated Test Result:

PLE

Instability Catch Sign

Painful Catch Sign

Apprehension Sign

Positive

Negative

Positive

Negative

Positive

Negative

Positive

Negative

Instability positive

32

6

10

28

14

24

7

31

Instability negative

8

76

12

72

23

61

10

74

Table 3.

Sensitivity, Specificity, Predictive Values, and Likelihood Ratios of Each Test for Lumbar Spinal Instability

Test

Sensitivity
(%)

Specificity
(%)

Positive
Predictive
Value (%)

Negative
Predictive
Value (%)

Positive Likelihood
Ratio (95%
Confidence Interval)

Passive lumbar extension

84.2

90.4

80.0

92.7

8.84 (4.51–17.33)

Instability catch sign

26.3

85.7

45.5

65.5

1.84 (0.87–3.89)

Painful catch sign

36.8

72.6

37.8

71.8

1.35 (0.78–2.32)

Apprehension sign

18.4

88.1

41.2

70.5

1.55 (0.64–3.76)

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surgery with spinal instrumentation such as a pedicle
screw system and plate fixation.

Twenty-five (62.5%) of 40 subjects with positive PLE test
results in this study eventually underwent spinal fusion
surgery. We cannot conclude only from the results of
this study that surgery always is indicated for subjects
with positive PLE test results, but we suggest that not
simply spinal decompression but spinal fusion should be
performed for subjects with positive PLE test results.

The radiological assessment of lumbar spinal instability
with the criteria established in this study showed that 38
of the 122 subjects had lumbar spinal instability, with a
pretest probability (prevalence) of 31.1%. This high
prevalence may have occurred because the number of
patients at our clinic who were referred from other
clinics or requested surgical treatment for lumbar spinal
instability at the initial visit was higher than the number
of patients with common lumbar degenerative diseases.
If a similar study were conducted with general patients
with lumbar degenerative diseases, it is thought that the
prevalence and the positive predictive value would
decrease and the negative predictive value would
increase. To assess the external validity, therefore, we
suggest that a study needs to be conducted with general
patients with lumbar degenerative diseases in the future.
On the basis of the sensitivity, specificity, and positive
likelihood ratio of the PLE test conducted in this study,
however, we believe that the PLE test has high validity.

With regard to the evaluation of lumbar spinal instabil-
ity, some studies have reported that radiographic find-
ings are not always consistent with clinical symp-
toms.

10,21–23

The reason may be that when patients

perform flexion and extension of the lumbar spine, they
use their discretion, fearing the occurrence of lumbar
pain, and thus may not actually perform maximal flexion
or extension. When the PLE test is conducted, lumbar
spinal extension is strong, leading to tension in the
anterior longitudinal ligament or the fibrous ring of the
intervertebral disk and relaxation in the zygapophyseal
capsule, to which surrounding mechanoreceptors or
nociceptors react strongly and induce lumbar pain. In
this respect, the PLE test serves to assess the reappear-
ance of painful clinical symptoms at the time of simple
extension of the lumbar spine because pain is caused by
passive extension of the lumbar spine.

The limitations of this report are as follows. The sam-
pling was unique because many of the subjects of this
study had relatively severe clinical symptoms; the assess-
ment of the pain in the lumbar region by the PLE test
was ambiguous; the subjects elevated their lower extrem-
ities to a height of about 30 cm in the PLE test, but the
height was somewhat variable; and the mechanism of a

positive PLE test result in lumbar spinal instability-positive
subjects was not clarified. Therefore, we suggest that stud-
ies to solve these limitations are needed in the future.

Conclusion
The sensitivity and specificity of the PLE test were 84.2%
and 90.4%, respectively. These values were higher than
those of other tests. The positive likelihood ratio for the
PLE test was 8.84; therefore, this test is an effective
method for evaluating lumbar spinal instability and can
be performed easily in an outpatient clinic.

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