Endoscopic decompression for intraforaminal and extraforaminal nerve root compression.

Abstract

The purpose of this study was to evaluate the outcome of endoscopic decompression surgery for intraforaminal and extraforaminal nerve root compression in the lumbar spine.
The records from seventeen consecutive patients treated with endoscopic posterior decompression without fusion for intaforaminal and extraforaminal nerve root compression in the lumbar spine (7 males and 10 females, mean age: 67.9 ± 10.7 years) were retrospectively reviewed. The surgical procedures consisted of lateral or translaminal decompression with or without discectomy. The following items were investigated: 1) the preoperative clinical findings; 2) the radiologic findings including MRI and computed tomography-discography; and 3) the surgical outcome as evaluated using the Japanese Orthopaedic Association scale for lower back pain (JOA score).
All patients had neurological findings compatible with a radiculopathy, such as muscle weakness and sensory disturbance. MRI demonstrated the obliteration of the normal increased signal intensity fat in the intervertebral foramen. Ten patients out of 14 who underwent computed tomography-discography exhibited disc protrusion or herniation. Selective nerve root block was effective in all patients. During surgery, 12 patients were found to have a protruded disc or herniation that compressed the nerve root. Sixteen patients reported pain relief immediately after surgery.
Intraforaminal and extraforaminal nerve root compression is a rare but distinct pathological condition causing severe radiculopathy. Endoscopic decompression surgery is considered to be an appropriate and less invasive surgical option.

Full text

Page 1

RESEARCH ARTICLEOpen Access
Endoscopic decompression for intraforaminal and
extraforaminal nerve root compression
Toshio Doi*, Katsumi Harimaya, Yoshihiro Matsumoto, Osamu Tono, Kiyoshi Tarukado and Yukihide Iwamoto
Abstract
Objective: The purpose of this study was to evaluate the outcome of endoscopic decompression surgery for
intraforaminal and extraforaminal nerve root compression in the lumbar spine.
Methods: The records from seventeen consecutive patients treated with endoscopic posterior decompression
without fusion for intaforaminal and extraforaminal nerve root compression in the lumbar spine (7 males and 10
females, mean age: 67.9 ± 10.7 years) were retrospectively reviewed. The surgical procedures consisted of lateral or
translaminal decompression with or without discectomy. The following items were investigated: 1) the
preoperative clinical findings; 2) the radiologic findings including MRI and computed tomography-discography; and
3) the surgical outcome as evaluated using the Japanese Orthopaedic Association scale for lower back pain (JOA
score).
Results: All patients had neurological findings compatible with a radiculopathy, such as muscle weakness and
sensory disturbance. MRI demonstrated the obliteration of the normal increased signal intensity fat in the
intervertebral foramen. Ten patients out of 14 who underwent computed tomography-discography exhibited disc
protrusion or herniation. Selective nerve root block was effective in all patients. During surgery, 12 patients were
found to have a protruded disc or herniation that compressed the nerve root. Sixteen patients reported pain relief
immediately after surgery.
Conclusions: Intraforaminal and extraforaminal nerve root compression is a rare but distinct pathological condition
causing severe radiculopathy. Endoscopic decompression surgery is considered to be an appropriate and less
invasive surgical option.
Background
Intraforaminal and extraforaminal nerve root compres-
sion at lumbar lesions is much rarer than intraspinal
canal lesions, making the diagnosis difficult [1]. The dif-
ficulties in making a correct diagnosis could unfortu-
nately result in a failed lumbar spine surgery.
Surgical intervention is considered for patients with
severe radiculopathy that does not respond to conserva-
tive treatment. As interverebral foraminal nerve entrap-
ment mostly affects the elderly, it is better to choose a
minimally-invasive surgical procedure. Consequently, we
have treated patients with intraforaminal and extrafor-
aminal nerve root compression by posterior decompres-
sion surgery without fusion. This procedure can obtain
clear visualization of the deep surgical field with mini-
mal damage to the posterior lumbar structure [2-5].
The purpose of this study was to elucidate the radiolo-
gical findings, including those obtained by computed
tomography-discography, and the surgical outcomes and
limitations of posterior decompression without fusion
for this relatively uncommon disease.
Methods
Seventeen patients (7 males and 10 females, mean age at
the time of surgery: 67.9 ± 10.7 years, range: 40 - 88
years) with intervertebral foraminal entrapment were
treated by endoscopic posterior decompression at
Kyushu University Hospital from 2008 to 2010. The
mean follow-up period was 10.8 moths (range: 4 - 20
months). All patients had leg pain that did not respond
to conservative treatment, such as NSAIDs, epidural
steroid injection or the use of a brace. Three patients
* Correspondence: toshidoi@ortho.med.kyushu-u.ac.jp
Department of Orthopaedic Surgery, Graduate School of Medical Sciences,
Kyushu University, Fukuoka, Japan
Doi et al. Journal of Orthopaedic Surgery and Research 2011, 6:16
http://www.josr-online.com/content/6/1/16
© 2011 Doi et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.

Page 2

had a history of previous lumbar surgery, including pos-
terior decompression of the spinal canal. They had
experienced only slight improvement after the previous
surgeries.
A diagnosis of intraforaminal or lateral entrapment was
established in each patient based on the results of both
neurological and radiological examinations. MR imaging
were performed in all patients. We performed CT disco-
grams for all but 3 patients to describe the positional rela-
tionship of the protruded disc to the posterior elements,
such as the facet, transverse process and pars interarticu-
laris, and such information was very useful for selecting
the optimal surgical approach. Selective nerve root blocks,
using 0.8 ml of 1% lidocaine, were also performed.
Surgical procedures
Posterior decompression was performed using a micro-
endoscope in all patients. Fourteen patients underwent
the extraforaminal approach [3] and 2 patients under-
went the translaminar approach [6,7]. In addition to
decompression of extraforaminal lesions, one patient
also underwent intraspinal canal decompression because
it was though likely that the intraspinal canal lesions
could not be excluded prior to the index surgery. The
METRx MED system (Medtronic Sofamor Danek) was
used for the entire procedure. The patient was placed
prone on a Hall frame. A skin incision of 2 cm was
made about 2 to 5 cm lateral to the spinous process.
After a muscle splitting approach using a series of
sequential dilators, a tubular retractor with a diameter
of 1.6 cm was set. For the translaminar approach, a
small oval fenestration about 8 mm in the hemilamina,
craniomedially to the facet joint, was performed (Figure
1E). For the extraforaminal approach, the muscles
attached to the inferior transverse process and the lat-
eral edge of the facet were removed, and the vertebral
disc was isolated from the superior-medial portion of
the inferior transverse process. In case of the extrafor-
aminal herniation, the herniated disc may have pro-
truded in this lesion (Figure 2B). The nerve root was
also identified in this lesion or that just cranial to the
disc. In case of a protruded disc, the disc just caudal to
the nerve root was removed using curetts and a punch.
No attempts were made to remove the osteophytes of
the vertebral body. The patients were then encouraged
to stand up and walk on the day after surgery.
Preoperative and Postoperative Evaluations
The following items were investigated: 1) the preopera-
tive radiological findings, including MRI and disco-CT
scans; 2) intraoperative disc protrusion; and 3) the surgi-
cal outcomes evaluated using the JOA score for lower
back pain (Table. 1).
Results
Clinical Findings
The neurological findings during the physical exam var-
ied in each patient (Table 2). The Kemp sign was posi-
tive in 13 (76%) patients. The nerve root stretching test
(FNST or SLRT) was positive in 11 (65%) patients. In
cases with L3 or L4 nerve root involvement, the femoral
nerve stretching test was frequently positive.
Radiological Findings
MR imaging was performed in all 17 cases. On MR
images, central spinal canal stenosis was not evident in
any patient. Parasagittal MRI at the foramen was use-
ful in assessing the presence of foraminal stenosis by
the obliteration of the normal increased signal inten-
sity fat (Figure 1A). CT-discography was performed
(Figure 1B, C) in 14 patients. Ten patients showed disc
protrusion in the foraminal (2 cases) or extraforaminal
(8 cases) lesion. A nerve root block with a local
anesthesic immediately relieved the radicular pain in
all 17 patients.
Intraoperative disc protrusion
During the intraoperative observations, 13 patients were
noted to have a protruding disc just caudal or anterior
to the nerve root. Among these, 2 cases had a herniated
disc just anterior to the nerve root, and the nerve root
seemed wide and flat just anterior to the lateral facet,
such that the herniated disc could only be found after
exploration of the anterior lesion of the nerve root. In
the cases with intraforaminal herniated disc removed by
the translaminar approach, a herniated disc was found
just caudal to the existing nerve root. Four cases had no
disc protrusion, and only lateral fenestration, including
the resection of some ligamentum flavum without dis-
cectomy, was performed.
The intraoperative findings with or without disc pro-
trusion were compatible to the CT-discogram findings
in all 14 cases who had undergone this examination.
Surgical outcomes
Sixteen patients reported relief of their preoperative
symptoms just after the surgery. One patient reported
no pain relief. Three patients had later recurrence of the
same symptoms on the ipsilateral side, and 2 patients
had later appearance of symptoms on the contralateral
side of the surgery. The mean JOA scores were 10.8
before surgery and 20.2 at the final follow-up, and the
mean recovery rate was 54%.
No serious complications occurred in any of the
patients during the surgical procedure. Two patients
who had symptoms of remaining leg pain had revision
surgery by PLIF.
Doi et al. Journal of Orthopaedic Surgery and Research 2011, 6:16
http://www.josr-online.com/content/6/1/16
Page 2 of 7

Page 3

Figure 1 Case 6. Images from a 56-year-old male who presented with severe right leg pain. A: Para-sagittal MRI imaging (T1) showed the
obliteration of the normal increased signal intensity fat (arrow). B,C: Para-sagittal and axial reconstruction CT-discograms showed an
intraforaminal herniated disc (arrow) at the L5-S1 level. D: A CT-discogram obtained at L5-S1 showing partial resection in the L4 lamina (arrow).
E: Postoperative 3-D reconstruction showing the oval fenestration in the L4 lamina.
Figure 2 Case 13. A three-dimensional CT-discogram obtained from a 78-year-old male who presented with severe left leg pain. (A)
The herniated disc (*) was located from the intraforaminal to the extraforaminal lesion. (B) A tubular retractor was set at the dotted area, and
the herniated disc (*) was removed.
Doi et al. Journal of Orthopaedic Surgery and Research 2011, 6:16
http://www.josr-online.com/content/6/1/16
Page 3 of 7

Page 4

Discussion
The diagnosis of intraforaminal and extraforaminal
nerve root compression is difficult to establish based on
a single diagnostic modality. Comprehensive clinical and
radiological information are required. Patients with this
disease present with unilateral leg pain and demonstrate
deficits of exiting nerve root function, including muscle
weakness of the lower extremities. The Kemp sign,
which induces a narrowing of the foraminal and
extraforaminal area by forcing dorsolateral extension of
the lower back, was positive in most patients.
Radiologically, parasagittal MRI at the foramen was
useful for assessing the presence of foraminal stenosis
by the obliteration of the normal increased signal inten-
sity fat. In our series, all 17 patients had features of for-
aminal stenosis on MRI, however, it was difficult to
determine whether the location of stenosis was intrafro-
mainal or extraforaminal in many cases. The causes of
stenosis in lateral lesions were a combination of pro-
truded discs, degenerated ligamentum flavum, protruded
osteophytes of the vertebral body, and degenerative
facets. It was difficult to determine which element(s)
had caused the nerve entrapment based on the findings
of MRI alone.
CT discography was therefore useful for elucidating
the participation of the protruded disc for the nerve
root entrapment at the lateral area. All cases that were
speculated to have a protruded disc by CT discography
also demonstrated corresponding surgical findings. The
3-D reconstruction of CT discograms could describe the
protrusion of the vertebral disc, especially compared to
the plane CT (Figure 3A, B). Three-dimensional recon-
struction of CT discograms can also describe the posi-
tional relationship of the protruded disc to the facet,
transverse process and pars (Figure 2A, B). These fea-
tures were very useful for the planning of the surgical
approach, especially since the endoscopic surgery can
only expose a small posterior element of the lumbar
spine.
There are several posterior decompression approaches
for performing intraforaminal and extraforaminal nerve
root compression at the lumbar spine. These include
the interlamina approach [8], translamina approach [6,7]
and extraforaminal approach [3,9-11]. For the interla-
mina approach, the performance of a medial facetect-
omy with laminotomy may provide an adequate
exposure of medial foraminal lesions. However, this pro-
cedure is usually limited to the L5-S1 level because the
lamina at other levels is not wide enough to perform a
resection. For the translaminar approach, a small oval
fenestration in the hemilamina, craniomedially to the
facet joint, was performed. The translaminar approach is
usually applied at either the L3-L4 or the L4-L5 level,
because the lamina at L1 or L2 may be too thin to
make an oval hole to preserve the pars interarticularis
and the disc level at the L5-S1 level is usually too caudal
for this approach. For the extraforaminal approach, the
removal of the intertransversarious ligament may ade-
quately expose the lateral compartment. At the L5-S1
level, since the space between the sacral ala and L5
transverse process is usually very narrow, the lateral
edge of the L5-S1 facet joint and the superior-medial
portion of the sacral ala were resected.
Table 1 Criteria for the JOA scoring system
Subjective symptoms (9 points)
low-back pain
none
occasionally mild
always present of sometimes sever
always sever
leg pain &/or numbness
none
occasionally mild
always present or sometimes sever
always sever
walking ability
normal walking
able to walk > 500 m, pain/numbness/weakness present
unable to walk 500 m due to pain/numbness/weakness
unable to walk 100 m due to pain/numbness/weakness
objective finding (6 points)
straight leg raising
normal
30-70 degree
< 30 degree
sensory function
normal
mild sensory disturbance
apparent sensory disturbance
motor function
normal (MMT normal)
slight decrease muscle strength (MMT good)
marked weakness (Grade 3-0)
restriction of ADLs (14 points) †
none
moderate
severe
bladder function (-6 points)
normal
mild dysuria
severe dysuria
total score
3
2
1
0
3
2
1
0
3
2
1
0
2
1
0
2
1
0
2
1
0
2
1
0
0
-3
-6
29
*ADL = activities of daily living; MMT = manual muscle testing.
†ADL include the following; turning over while lying down, standing, washing
one’s face, leaning forward, ability to sit for approximately 1 hour, ability to
lift or hold heavy objects, and ambulatory ability.
Doi et al. Journal of Orthopaedic Surgery and Research 2011, 6:16
http://www.josr-online.com/content/6/1/16
Page 4 of 7

Page 5

Table 2 Patient characteristics and outcomes
Age,
SexSign
Level KempSLRT FNST Sensory
Disturb
Muscle
Weakness
disc protrusion CT
discogram
Preop conservative
treatment
disc protrusion
op-finding
Preop JOA
score
Postop JOA
score
Recovery
Rate (%)
different
outcomes
1 88, FL5-S1 +-- L5-+3 M+3 1130.8 Contralateral
side*
31.8 Contralateral
side
0 no pain relief
41.2 Ipsilateral
side†
50
100
93.3 Ipsilateral side
62.5
100
88.9
55.6
33.3
27.8
88.9 Ipsilateral side
43.8
43.8
28
54.1 ± 30.0
2 69, F L3-L4 +++ L4 IP, QF, EHL+ 5 M+7 14
3 70, F
4 80, F
L5-S1 +
L5-S1 +
-
-
-
-
L5
L5
-
EHL
-
-
2 M
2 M
-
-
12
12
12
19
5 70, F
6 56, M
7 76, F
8 75, F
9 67, M
10 60, M
11 68, M
12 40, F
13 78, M
14 66, M
15 63, F
16 66, M
17 62, F
L5-S1 +
L4-L5 +
L3-L4 -
L5-S1 +
L5-S1 +
L5-S1 +
L5-S1 -
L5-S1 -
L5-S1 +
L5-S1 -
L3-L4 +
L3-L4 +
L4-L5 +
+
+
-
-
+
+
-
+
-
+
+
-
-
-
+
+
-
-
-
-
-
-
-
-
+
+
L5
L4
-
L5
L5
L5
L5
L5, S1
L5
L5
L3
L3
-
EHL
-
-
EHL
EHL
EHL
-
-
EHL
EHL
-
IP, QF
EHL
+
+
+
+
+
NA
+
+
+
-
NA
+
NA
5 M
14 M
6 M
8 M
9 M
4 M
5 M
2 M
6 M
4 M
7 M
4 M
18 M
+
+
+
+
+
+
+
+
+
-
+
+
+
11
15
14
5
8
11
11
14
11
20
13
13
4
20
29
28
20
29
27
21
19
16
28
20
20
11
10.8 ± 4.3 20.2 ± 6.2
* contralateral side = later recurrence of the same symptom on the contralateral side of the surgery.
† ipsilateral side = later appearance of symptoms on the contralateral side of the surgery.
Doi et al. Journal of Orthopaedic Surgery and Research 2011, 6:16
http://www.josr-online.com/content/6/1/16
Page 5 of 7