Congenital absence of lumbosacral articular facet joint associated with conjoined nerve root: a case report.

Abstract

We report a rare case of congenital absence of the L5-S1 facet joint, which was associated with a conjoined nerve root. Combination of these two anomalies has been quite rarely reported in the literature. A 39-year-old man presented with acute low back pain and right leg radiating pain. Muscle weakness and sensory disturbance of the right leg were also apparent in the region innervated by L5 and S1 nerve roots. Preoperative multidetector three-dimensional computed tomography (3D-CT) showed complete absence of the right S1 superior articular process. Magnetic resonance (MR) images showed lumbar disc herniation at right L5-S1 level that migrated cranially. Intraoperative findings revealed that the right L5 nerve root and S1 nerve root were conjoined, and the conjoined nerve root was compressed by L5-S1 disc herniation, which led to impairment of the conjoined nerve root by a single-level lumbar disc herniation. After removal of the disc herniation, his right leg pain immediately subsided, however muscle weakness and sensory disturbance persisted. Surgeons should be aware of this nerve root anomaly when examining a patient who shows an unusual clinical presentation and/or congenital osseous anomaly.

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CASE REPORT
Congenital absence of lumbosacral articular facet joint associated
with conjoined nerve root: a case report
Shinji Yoshioka•Koichi Sairyo•Toshinori Sakai•
Natsuo Yasui
Received: 24 November 2009/Accepted: 7 July 2010/Published online: 29 July 2010
? The Author(s) 2010. This article is published with open access at Springerlink.com
Abstract
the L5-S1 facet joint, which was associated with a con-
joined nerve root. Combination of these two anomalies has
been quite rarely reported in the literature. A 39-year-old
man presented with acute low back pain and right leg
radiating pain. Muscle weakness and sensory disturbance
of the right leg were also apparent in the region innervated
by L5 and S1 nerve roots. Preoperative multidetector three-
dimensionalcomputedtomography
complete absence of the right S1 superior articular process.
Magnetic resonance (MR) images showed lumbar disc
herniation at right L5-S1 level that migrated cranially.
Intraoperative findings revealed that the right L5 nerve root
and S1 nerve root were conjoined, and the conjoined nerve
root was compressed by L5-S1 disc herniation, which led
to impairment of the conjoined nerve root by a single-level
lumbar disc herniation. After removal of the disc hernia-
tion, his right leg pain immediately subsided, however
muscle weakness and sensory disturbance persisted. Sur-
geons should be aware of this nerve root anomaly when
examining a patient who shows an unusual clinical pre-
sentation and/or congenital osseous anomaly.
We report a rare case of congenital absence of
(3D-CT)showed
Keywords
Anomaly ? Lumbar disc herniation
Conjoined nerve root ? Facet joint ?
Introduction
Congenital absence of the lumbosacral articular facet joint
is an uncommon anomaly [1–12]; it is usually asymptom-
atic and sometimes presents with a concomitant nerve root
anomaly. To our knowledge, only three cases of congenital
absence of the lumbosacral articular facet joint and a
concomitant conjoined nerve root have been reported in the
literature [9, 12].
We report a symptomatic case and the outcome of
treatment.
Case report
A 39-year-old man presented with acute low back pain and
right leg radiating pain. He had no history of trauma or
other trigger event. His symptoms had rapidly worsened
until he was not able to walk because of right foot drop and
severe leg pain. He was diagnosed a lumbar disc herniation
at L5-S, and was referred to our hospital for surgical
treatment.
Neurological examinations showed a positive straight-
leg raising test at 30? on the right side. On manual muscle
test (MMT), muscle weakness was found in the right leg:
tibialis anterior was 1/5, extensor hallucis longus was 0/5,
right flexor hallucis longus was 3/5, and triceps surae was
3/5. The right patella tendon reflex was normal and the
right ankle jerk reflex was diminished. Hypoesthesia was
noted in the right region innervated by L5 and S1 nerve
roots. Neurologically, L5 and S1 nerve roots impairment
was indicated. These findings were unusual symptoms of
single-level lumbar disc herniation at L5-S1.
From plain anteroposterior (AP) and lateral radiographs
of the lumbar spine, it was difficult to detect some spinal
S. Yoshioka ? K. Sairyo (&) ? T. Sakai ? N. Yasui
Department of Orthopedics, Institute of Health Biosciences,
The University of Tokushima Graduate School,
3-18-15 Kuramoto-cho, Tokushima 770-8503, Japan
e-mail: sairyokun@hotmail.com
123
J Orthopaed Traumatol (2010) 11:183–187
DOI 10.1007/s10195-010-0100-4

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abnormalities. Slight disc space narrowing at L5-S1 was
seen on the lateral view (Fig. 1). Myelographs showed
incomplete blockade at the L5 pedicular level, especially
on the right side (Fig. 2). Computed tomography (CT)
following myelography showed absence of the right L5-S1
facetjoint(Fig. 3).Multidetectorthree-dimensional
Fig. 1 Plain AP and lateral
radiographs of the lumbar spine.
Despite slight disc space
narrowing at L5-S1, there was
no clear abnormality
Fig. 2 Myelograms showing
incomplete block at L5
pedicular level, especially on
the right side (arrows)
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computed tomography (3D-CT) confirmed the absence of
S1 superior articular process (Fig. 4). Magnetic resonance
(MR) images showed disc herniation on the right side at the
L5-S1 intervertebral disc level (Fig. 5a). Axial MR
T2-weighted images at the L5-S disc level showed disc
herniation (Fig. 5b, left panel), which migrated cranially
(Fig. 5b, right panel). Based on the above neurological and
radiological investigations, we diagnosed the patient as
having a migrating mass that compressed the L5 nerve root
and disc level lumbar disc herniation that compressed the
S1 nerve root, causing these symptoms.
At first, to detect the L5 nerve root, we performed a
fenestration at the right L4-5 using a microscope. At the
L4-5 level, no nerve root was found, and right L5 hemi-
laminectomy was additionally conducted.
We found that the L5 nerve root originated from the
caudal level of the L5 pedicle and conjoined with the S1
nerve root (Fig. 6). The large disc herniation at L5-S1
migrated cranially and was found beneath the abnormal
conjoined nerve roots. After removal of the disc herniation
and unroofing of the nerve root, no obvious mobility of the
conjoined nerve root was obtained.
Postoperatively, leg pain immediately disappeared and
muscle weakness slightly improved 3 months later: MMT
of the right tibialis anterior and extensor hallucis longus
became 2/5, and that of the right flexor hallucis longus and
triceps surae became 5/5. At follow-up examination
1 month later, axial MR T2-weighted images from the S1
pedicle level showed the two confluent (L5 and S1) rootlets
(Fig. 7). At present, our patient can walk with an ankle–
foot orthosis without a cane. The patient was informed that
data concerning the case would be submitted for publica-
tion, and he consented.
Fig. 3 CT performed following myelography, showing absence of
the right L5-S1 facet joint
Fig. 4 3D-CT showing complete absence of the S1 superior articular
process (circle)
Fig. 5 a MR sagittal images showing disc herniation at L5-S1
intervertebral disc level. b Axial MR T2-weighted images showing
the herniated nucleus pulposus (HNP, left panel), which migrated
cranially (b, right panel)
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Discussion
Congenital absence of the lumbosacral articular facet joint
is rare, with only 25 cases reported in the English-language
literature [1–12]. In the past cases, the L5-S1 facet joint
was mostly affected (80%). Rowe et al. found only one
case of congenital absence of the inferior articular process
of L5 in 1,539 specimens [11]. Roche et al. studied 4,200
skeletons and failed to find this anomaly [10].
The etiology of this anomaly is generally accepted as
follows: there are three primary ossification centers in each
vertebra: one center in the vertebral body and two in the
neural arches [5, 6, 8, 11, 13]. The facet defect is thought to
originate from a failure of these ossification processes.
However, the true etiology has not been clarified.
Although congenital absence of the lumbosacral artic-
ular facet joint seems to cause spinal instability, in only 3
of 25 cases was spinal fusion performed [5, 7, 13]. Most of
the symptomatic patients were treated with conservative
therapy and became asymptomatic. Only in severe cases
must surgical fusion of the vertebra be performed. Because
ofthe small numberof
controversial.
Conjoined nerve roots are relatively common anomalies
of the lumbosacral spine. Numerous cases have been
reported in the literature [2, 9, 12, 14–26]. The incidence of
lumbosacral conjoined nerve roots varies among reports.
Kadish et al. found eight conjoined nerve roots in 100
cadavers (8% incidence) [22]. Recently, Artico et al.
reported that 0.25% of 1,200 patients who underwent CT or
MRI had conjoined nerve roots [2]. Kadish et al. also
reported that conjoined L5 and S1 roots are the most fre-
quent (52.2%) [22]. Postacchini et al. stated that lumbo-
sacral nerve root anomalies were almost asymptomatic and
sometimes presented with symptoms by disc herniation [9].
The present case showed both anomalies, i.e., complete
absence of the superior articular process of S1 and con-
joined L5 and S1 nerve roots, which were symptomatically
compressed by a large disc herniation. Osseous anomalies
in the lumbosacral spine associated with conjoined nerve
roots such as this case have been rarely reported. However,
Rask stated that the presence of congenital osseous defects
of the lumbosacral spine should indicate presence of nerve
cases,treatmentremains
Table 1 Summary of previous cases of congenital absence of the lumbosacral articular facet joint associated with conjoined nerve root
CaseAuthorsSex, age (years) SymptomsLocation of anomalies Conjoined nerve roots Presence of HNP
1Postacchini et al. [19] UnknownUnknownL5-S1L5 & S1-
2Savas et al. [24]Unknown LBPL5-S1L5 & S1-
3 Savas et al. [24]UnknownLBPL5-S1L5 & S1-
Present case Yoshioka et al.Male, 39 LBP, leg pain, palsy L5-S1L5 & S1?
HNP herniated nucleus pulposus, LBP low back pain
Fig. 6 Schema of anomalies in this case. The absence of the S1
superior articular processes was obvious, and the L5 and S1 nerve
roots were conjoined
Fig. 7 Sagittal MR images obtained 1 month after the surgery,
showing two confluent (L5 and S1) rootlets (arrows)
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root anomalies [24]. To our knowledge, there have been 11
cases, including defect or anomaly of the vertebral arch,
spondylosis, spondylolisthesis, and bifid sacrum, present-
ing with conjoined nerve roots [9, 11, 12, 15, 17, 24–26].
Only three previous cases were similar to the present case
(Table 1) [9, 12].
In summary, we report a quite rare case of congenital
absence of lumbosacral articular facet and conjoined nerve
root. Surgeons should be aware of this nerve root anomaly
when a patient shows an unusual clinical presentation and/
or congenital osseous anomaly.
Conflict of interest
None.
Open Access
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