Changes in nerve root motion and intraradicular blood flow during intraoperative femoral nerve stretch test

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1. ONVENTIONALmedical therapy is based on a diagno-
sis made by synthesizing information acquired from
the patient’s history, physical examination, and spe-
cial investigations. Recent developments in diagnostic neu-
roimaging procedures such as MR imaging have made it
easy to visualize hernia-induced nerve root compression,
assisting in the diagnosis of lumbar disc herniation. A com-
pressed nerve root does not always cause pain. In approxi-
mately 20 to 30% of individuals with no history of radicu-
lar pain, abnormal findings are demonstrated on imaging
studies.
2,11,17,43
It is difficult to obtain information relevant
to pain from such diagnostic imaging, however, and thus
patient history and neurological examination remain im-
portant aspects of the workup. Nerve stretch examinations,
such as the FNST and SLR test, are performed to deter-
mine whether there is evidence of nerve root irritation, usu-
ally as a consequence of lumbar disc prolapse. Along with
anterior thigh pain, the FNST provides one of the most
important signs because it indicates mechanical fixation of
the nerve root, a state amenable to surgery.
1,12,27,31,37
Its ab-
sence is a discouragement to surgery. It is generally be-
lieved that nerve root compression is caused by the herni-
ated disc when the knee joint is flexed with the hip joint
kept in hyperextension, resulting in the onset of lumbar
pain or anterior thigh pain. It remains unclear, however,
exactly how the nerve roots of the upper lumbar region are
affected by the FNST in vivo. Additionally it must be noted
that false-positive FNSTs have been reported in association
with osteoarthritis of the hip, diabetic neuropathy,
4
ruptured
aortic aneurysm,
38
retroperitoneal hemorrhage,
39
epidural
hematoma,
20
anticoagulation therapy,
6
and retroperitoneal
tumors.
44
The FNST may compromise the nerve roots con-
tributing to the femoral nerve and even the L-5 nerve.
5
The circulatory dynamic of lumbosacral nerve roots is
obviously of great importance in degenerative disease of
J Neurosurg (Spine 3) 99:298–305, 2003
298
Changes in nerve root motion and intraradicular blood flow
during intraoperative femoral nerve stretch test
Report of four cases
SHIGERUKOBAYASHI, M.D., PH.D., YOSHIHIKOSUZUKI, M.D., PH.D., TAKAHIROASAI, M.D., PH.D.,
ANDHIDEZOYOSHIZAWA, M.D., PH.D.
Physiology Laboratory of Oxford University, Oxford, United Kingdom; and Department of Orthopedics,
Fujita Health University School of Medicine, Aichi, Japan
Object. It is not known whether changes in intraradicular blood flow (IRBF) occur during the femoral nerve stretch
test (FNST) in patients with lumbar disc herniation. An FNST was conducted in patients with lumbar disc herniation to
observe the changes in IRBF, and results were then compared with clinical features.
Methods. The study was composed of four patients with L3–4 disc herniation who underwent microdiscectomy.
Patients were placed prone immediately before surgery, so that their knee flexed on the operating table with the hip joint
kept in hyperextension, and the FNST was performed to confirm at which region pain developed in the anterolateral
thigh. During the operation, the hernia-affected nerve roots were visualized under a microscope. The needle sensor of
a laser Doppler flowmeter was then inserted into each nerve root immediately above the hernia, and the change in IRBF
was measured during the intraoperative FNST. After removal of the herniated disc, a similar procedure was repeated
and IRBF was measured again.
The intraoperative FNST showed that the hernia compressed the nerve roots and there was marked disturbance of
gliding, which was reduced to only a few millimeters. During the test, IRBF decreased by 92.8 to 100% (mean 96.9
3.7% [standard error of the mean]) relative to the blood flow before the test. This study demonstrated that the blood
flow in the nerve root is reduced when the nerve root is compressed in vivo.
Conclusions.The intraoperative FNST showed that the hernia compressd the nerve roots and there was marked distur-
bance of gliding, which was reduced to only a few millimeters. During the test, IRBF decreased by 92.8 to 100% (96.9
3.7% [mean standard error of the mean]).
KEYWORDS•nerve root • disc herniation • femoral nerve stretch test •
intraradicular blood flow • laser Doppler flowmeter • lumbar spine C
J. Neurosurg: Spine / Volume 99 / October, 2003
Abbreviations used in this paper:FNST = femoral nerve stretch
test; IRBF = intraradicular blood flow; MR = magnetic resonance;
SLR = straight leg raising.

2. spine.
7,24,36
In experimental studies, many models of acute
8,14,
21,23–25,35,45,46
and chronic
19,47
nerve root compression have
been created and studied pathologically and electrophysi-
ologically. The results to date suggest that impaired IRBF
and nerve fiber deformation are implicated in the mani-
festation of radicular symptoms associated with nerve root
compression; however, it is not clear if an acute reduction
of blood flow induces pain. Therefore, we studied the ex-
tent to which blood flow is disturbed in the nerve roots
when sciatica results from lumbar disc herniation.
In the FNST performed intraoperatively, we used a laser
Doppler blood flowmeter to evaluate the extent of the
IRBF disturbed at various angles and which caused ante-
rior thigh pain.
Case Reports
Patient Population
Four patients with lumbar disc herniation underwent
microdiscectomy. There were three men and one woman,
who ranged in age 27 to 42 years (mean 34 years). All
patients initially received adequate conservative treatment
such as analgesic therapy and an epidural block and un-
derwent MR imaging every 3 months; however, due to
unresolved sciatica, they elected to undergo surgery. The
details of this study were explained to the patients before
obtaining informed consent. The L3–4 disc space was sur-
gically treated in all four patients. The mean preoperative
duration of anterior thigh pain was 9.3 months (range
6–13 months).
Intraoperative FNST
Before conducting the intraoperative FNST, so as not to
cause excessive distraction of the nerve roots after induc-
tion of anesthesia, the patients lay prone on the operating
table and we performed the FNST to confirm the presence
of anterolateral thigh pain (Fig. 1). The FNST indicated a
positive response in each patient, but the SLR test demon-
strated painless restriction.
The operation was performed after induction of general
anesthesia, and each patient was placed prone with both
legs extended. First, using an operating microscope, we
confirmed that the nerve roots were compressed by the her-
nia and then performed an intraoperative FNST by flexing
the patient’s knee joint on the affected side with the hip
joint hyperextended.
Measurement of Nerve Root Motion
To assess the translocation movement of a nerve root on
the affected side, a 27-gauge needle was inserted as a
marker into the margin of nerve root. The distance over
which the marker traveled was measured using callipers.
This measurement was performed before and after exci-
sion of the disc protrusion. If the hernia did not adhere to
the dura mater of the nerve roots, it was classified as
Grade 0; mild adhesions that were easily removed were
classified as Grade 1; and severe adhesions that were dif-
ficult to remove were classified as Grade 2.
Measurement of IRBF
The IRBF was measured using a laser Doppler flowme-
ter (LFB-III; Biomedical Sci. Co., Matsuoka, Japan). The
needle sensor of a laser Doppler flowmeter (500 m
diameter, LFN-50; Biomedical Sci. Co.) was inserted into
each nerve root immediately above the herniation (Fig. 2),
and we performed an intraoperative FNST by flexing the
patient’s knee joint on the affected side with the hip joint
hyperextended for 1 minute while the changes of the
IRBF were measured. This test was conducted three times
consecutively before removal of the herniated disc, after
which the sensor was again inserted into the nerve roots
and the test repeated to observe whether the IRBF had
improved. At this time, the FNST was conducted in all
patients.
Analysis of IRBF
By using a laser Doppler flow technique, we were able
to obtain real-time data, although spatial characterization
and quantitative measurement of blood flow are necessar-
ily sacrificed. We used Power Lab software (Chart Ver-
sion 3,4,6; AD Instruments, Colorado Springs, CO) for
analyzing the waveform of blood flow to obtain the mean
value for 10 seconds immediately before the test, for 10-
second periods from 20 and 50 seconds after initiation of
the test, and from 20 and 50 seconds after completion of
J. Neurosurg: Spine / Volume 99 / October, 2003
Intraradicular blood flow during FNST
299
FIG. 1. Photograph showing the FNST.
FIG. 2. Intraoperative measurement of IRBF. The blood flow
sensor (arrowhead)was inserted into L-4 nerve root (asterisk)
above the hernia.

3. the FNST. The blood flow value immediately before the
test was used as the baseline measurement, and those
obtained during and just after the test were expressed as a
percentage of baseline and are presented as the mean
standard error of the mean. Comparison of values was
performed using the Student t-test.
Results
Nerve Root Motion During the Intraoperative FNST
Intraoperatively, microscopic observation revealed that
a herniated mass adhered to the dura mater of the nerve
roots in all patients. The intraoperative FNST showed that
the hernia caused nerve root compression in all patients.
In three patients, the nerve roots showed no gliding dur-
ing FNST, which caused thigh pain before the operation,
and their movement was clearly disturbed (only 0–1 mm
at L-4 [mean 0.25 0.43 mm]). Whether the herniated
nucleus pulposus pierced the posterior longitudinal liga-
ment, the FNST caused the nerve root to be placed under
tension ranging from the herniated mass to the periphery;
at this time gliding adjacent to the herniated mass was
nearly absent and compression created flattening of the
nerve root. After removal of the lesion, the nerve roots
glided smoothly in all patients, its gliding distance at L-4
having increased (3–4 mm [3.75 0.5 mm]) during
FNST (Fig. 3).
Regarding prolapse of the herniation, subligamentous
extrusion was present in three cases and transligamentous
extrusion was observed in one. Regarding the severity of
the lesion’s adhesion to the dura of the nerve roots, Grade
S. Kobayashi, et al.
300 J. Neurosurg: Spine / Volume 99 / October, 2003
FIG. 3. Graph demonstrating changes of nerve root movement
before and after discectomy.
FIG. 4. Graph showing changes of IRBF during the FNST. The IRBF decreased by 96.9 3.7% (mean standard
error of the mean) in the nerve root and during the FNST test. Twenty seconds after test completion, IRBF showed a tran-
sient increase to 110% or greater in two of four patients. This transient increase of IRBF was attributed to the decreased
nerve root tension and also decreased the tension placed on the intraradicular blood vessels, both resulting from the effects
of the FNST.

4. 1 adhesion was demonstrated in one case and Grade 2
adhesion was demonstrated in three. In particular,
transligamentous hernias were associated with strong ad-
hesions to the dura mater and were difficult to separate
from the nerve root.
Intraradicular Blood Flow During Intraoperative FNST
During the FNST, there was a sharp decrease of IRBF
in the L-4 nerve root on the side ipsilateral to the antero-
lateral thigh pain in all the patients, and this reduction last-
ed during the time of FNST. At 20 and 50 seconds after
initiating the test, IRBF was decreased to 7.3 and 3.2%,
respectively. When the angle of the knee was retuned to
0˚, IRBF immediately improved, recovering to the base-
line value measured before the FNST. The IRBF recov-
ered by 105.3 and 104.2% at 20 and 50 seconds after com-
pletion of the test, respectively (Fig. 4). Twenty seconds
after test completion, IRBF increased transiently to 110%
or more in two of the four patients. This series of IRBF
changes was reproducible, confirmed by repeating the test
three times consecutively.
After removal of the hernia, the nerve roots exhibited a
smooth gliding motion in all patients. The intraoperative
FNST conducted after removal of the hernia showed no
significant decrease of IRBF in L-4 nerve roots and con-
firmed that discectomy had improved IRBF. Twenty sec-
onds after test completion, IRBF increased transiently to
110% or more in three patients. When the FNST was per-
formed 1 week postoperatively, results were negative in
all patients, and anterolateral thigh pain was not elicited in
any patient, unlike the results obtained preoperatively (Ta-
bles 1 and 2).
Illustrative Case
Case 1
This 29-year-old man had suffered an episode of antero-
lateral left thigh pain 1 year previously; the pain subsided
spontaneously. On examination, we found painless restric-
tion during the SLR test, but FNST reproduced the pre-
senting pain. During the FNST, when the patient’s knee
was passively flexed during hip extension, he experienced
not only sudden deep pain in the anterolateral thigh,
but also distinct paresthesias in the L-4 dermatome. The
quadriceps muscle was weak and the patellar reflex de-
pressed. Lumbar MR imaging (Fig. 5 upper left and right)
and myelography (Fig. 5 lower left, center, and right)
revealed a herniated disc at the L3–4 level compressing
the L-4 nerve root. He was treated conservatively, but be-
cause symptoms were not alleviated, the L-4 space was
explored microsurgically in June 1999. The nerve root
sleeve was adherent to the herniated disc. The type of her-
nia was transligamentous extrusion (Fig. 6). The needle
sensor of a laser Doppler flowmeter was inserted into L-4
nerve root above the hernia.
The IRBF at L-4 was decreased by 2.8 and 0% at 20 and
50 seconds after initiating the test, respectively. Intra-
operative FNST conducted after removal of the hernia
J. Neurosurg: Spine / Volume 99 / October, 2003
Intraradicular blood flow during FNST
301
TABLE 1
Prediscectomy data obtained in four patients undergoing FNST*
Op Findings FNST-Related IRBF Rate (%)†
Clinical Findings
Nerve Pre-
Age Sensory Type Ad- Root test Intratest Posttest
Case (yrs), Disturb- Weak- of hesion Motion
No. Sex Location FNST‡ ance ness Hernia Grade (mm) 1 2 3 4 5
1 27, M L3–4 yes yes yes T 2 0 100 2.8 0 110.4 107.6
2 38, F L3–4 yes yes no S 1 1 100 14.3 7.2 117.6 109
3 29, M L3–4 yes yes yes S 2 0 100 4.9 0 106 103
4 42, M L3–4 yes yes no S 2 1 100 7.2 5.6 87.3 97.2
*S = subligamentous extrusion; T = transligamentous extrusion.
†Period 1, 10 seconds prior to FNST; Periods 2 and 3, 20 and 50 seconds, respectively, after initiation of FNST; and Periods 4 and
5, 20, and 50 seconds, respectively, after completion of FNST.
‡Indicates whether the FNST induced an adverse (yes) or absent (no) response.
TABLE 2
Postdiscectomy data obtained in four patients
FNST-Related IRBF Rate (%)*
Op Findings
Pretest Intratest Posttest
Case Adhesion Root Motion Postop IRBF
No. Grade at FNST (mm) 1 2 3 4 5 (after 1 wk)
10 4 100 103.4 102.6 115.6 111 improved
20 4 100 110.5 103.1 120.3 108.3 improved
30 4 100 101 100.5 114.1 102.6 improved
40 3 100 93.2 97.8 103 99.5 improved
*Period 1, 10 seconds prior to FNST; Periods 2 and 3, 20 and 50 seconds, respectively, after initiation of FNST; and Periods 4 and
5, 20 and 50 seconds, respectively, after completion of FNST.

5. showed no significant decrease of IRBF in the L-4 nerve
roots, confirming that discectomy improved IRBF (Fig. 7).
Discussion
Despite the advent of modern tests, including MR im-
aging, the FNST remains one of the most important and
commonly used clinical tests in the diagnosis of a pro-
lapsed upper lumbar intervertebral disc. The FNST dem-
onstrates nerve root irritation at the L-2, L-3, and L-4 lev-
els and has provided one of the most significant of clinical
signs when diagnosing upper lumbar disc herniation and
evaluating the progress of this condition since Wasser-
mann
41,42
modified the test in 1918. Its value in the diag-
nosis of diabetic femoral neuropathy has been empha-
sized, but scant attention has been given to its usefulness
in patients with upper lumbar nerve root compression.
10
Dyck
9
hypothesized that the femoral stretching maneuver
applies direct traction forces on the upper lumbar nerve
roots due to stretching of the femoral nerve in the psoas
and quadriceps muscles. It has been observed that these
traction forces result in a 2-mm movement of the L-4
nerve root.
During surgery, microscopic observation revealed that a
herniated mass adhered to dura mater of the nerve roots in
all four patients. The intraoperative FNST showed that the
hernia compressed and flattened the nerve roots, resulting
in a clear disturbance in which the gliding distance was
reduced to only a few millimeters. Whether the herniated
nucleus pulposus pierced the posterior longitudinal liga-
ment, the FNST showed that the nerve root was placed
under tension from the site of the hernia to the periphery;
gliding movement was absent adjacent to the herniated
mass and compression flattened the nerve root. After
removal of the hernia, however, gliding and smoother
movement of the nerve roots indicated a clear improve-
S. Kobayashi, et al.
302 J. Neurosurg: Spine / Volume 99 / October, 2003
FIG. 5. Case 1. Neuroimages showing L3–4 disc herniation.Upper Left:Sagittal T
2-weighted (TR 2000 msec, TE
15 msec) MR image. Upper Right:Axial T
2-weighted (TR 2000 msec, TE 15 msec) MR image.Lower Left:Anterior
myelogram revealing a defect at the L3–4 disc level (arrow).Lower Center:Lateral radiograph obtained in flexion.
Lower Right:Lateral radiograph obtained in extension.

6. ment. Thus, it seems that nerve root tension caused by
chemical inflammation–induced adhesion of the hernia to
the dura may, in fact, be of greater importance than hernia-
related nerve root compression with respect to onset of
anterior thigh pain during the FNST. That is, even when
the hernia causes nerve root compression, the nerve root
will remain mobile and anterior thigh pain will be less
apparent in the absence of dural adhesions.
No previous studies have been conducted to measure
nerve root blood flow related to symptomatic lumbar disc
herniation in humans. Matsuzaki, et al.,
29
measured the
nerve root action potential during the intraoperative SLR
test in patients with disc herniation. In two of five patients,
the action potential was obtained at an SLR angle of 0˚
before removal of the herniated disc but disappeared when
the SLR angle was set at 90˚ for 5 minutes. Then the
action potential returned to the baseline value after 10
minutes when the angle was decreased to 30˚. These
changes probably resulted from disturbed blood flow in
the nerve roots because the same maneuvers did not alter
the potential after the herniated material was excised. In
our study, it was difficult to establish whether ectopic
nerve root discharge,
18,33
which was highly correlated with
pain, was attributable to which of the following cases: 1)
direct injury of nerve fibers due to mechanical compres-
sion or extraction of the hernia mass; or 2) disturbed blood
flow. It seems that the nerve roots become hypoxic when
pain is experienced during the FNST (or in the case of
neuropraxia) because IRBF decreased sharply when we
conducted the FNST; additionally, Matsuzaki, et al., re-
ported similar results in their electrophysiological study.
Analysis of the present results suggests that the mecha-
nism of inflammation around the lesion after disc hernia-
tion is different from that associated with demyelination
of nerve roots; this is supported by FNST results obtained
after removal of the hernia—that is, no disturbance of
IRBF and postoperative sciatica. The inflammatory reac-
tion around the hernia likely caused the adhesions be-
tween the lesion and the nerve root, which then reduced
the mobility of the nerve root during movement of the
legs. This led to severe nerve root tension or compres-
sion,
3,13,15,34
resulting in disturbance of IRBF and break-
down of the blood–nerve barrier, which in turn promoted
intraradicular inflammatory changes such as edema and
demyelination.
21,48
On the other hand, it is apparent from
the natural history of lumbar disc herniation that an
inflammatory reaction around the hernia is essential for
spontaneous involution of the mass,
16,22,26,28,30,32,40
although
it produces adhesion between the hernia and the nerve
roots. Therefore, control of the inflammatory reaction is
an important challenge when treating patients with disc
herniation.
J. Neurosurg: Spine / Volume 99 / October, 2003
Intraradicular blood flow during FNST
303
FIG. 6. Case 1. Intraoperative findings. The type of hernia was
transligamentous extrusion (arrow). The asteriskidentifies the L-4
nerve root.
FIG. 7. Case 1. Changes in IRBF during the intraoperative FNST.

7. Conclusions
Using the FNST, we found that hernias adhering to the
nerve roots disturbed gliding of the roots, causing nerve
root compression and tension as well as a reduction of
IRBF.
Disclaimer
No benefits in any form were or will be received from a commer-
cial party related directly or indirectly to the subject of this article.
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Manuscript received November 21, 2002.
Accepted in final form June 16, 2003.
Address reprint requests to:Shigeru Kobayashi, M.D., Ph.D.,
Department of Orthopaedics and Rehabilitation Medicine, School
of Medicine, Fukui Medical University, Shimoaizuki 23, Matsuoka,
Fukui, 910-1193, Japan. email: [email protected].
J. Neurosurg: Spine / Volume 99 / October, 2003
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