Congenital absence of lumbosacral articular facet joint associated with conjoined nerve root: a case report
© The Author(s) 2010
Received: 24 November 2009
Accepted: 7 July 2010
Published: 29 July 2010
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.
KeywordsConjoined nerve root Facet joint Anomaly Lumbar disc herniation
Congenital absence of the lumbosacral articular facet joint is an uncommon anomaly [1–12]; it is usually asymptomatic 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.
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.
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 hemilaminectomy was additionally conducted.
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 . Roche et al. studied 4,200 skeletons and failed to find this anomaly .
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 articular 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 of the small number of cases, treatment remains 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) . Recently, Artico et al. reported that 0.25% of 1,200 patients who underwent CT or MRI had conjoined nerve roots . Kadish et al. also reported that conjoined L5 and S1 roots are the most frequent (52.2%) . Postacchini et al. stated that lumbosacral nerve root anomalies were almost asymptomatic and sometimes presented with symptoms by disc herniation .
Summary of previous cases of congenital absence of the lumbosacral articular facet joint associated with conjoined nerve root
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
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