The authors reviewed the clinical and neurodiagnostic

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1 KISEP J Korean Neurosurg Soc 36 : Clinical Article Clinical Analysis of Extraforaminal Entrapment of L5 in the Lumbosacral Spine Jee-Soo Jang, M.D., 1 Sun-Hwa An, R.N., 1 Sang-Ho Lee, M.D. 2 Department of Neurosurgery, 1 Wooridul Spine Hospital, Gwangju, Korea Department of Neurosurgery, 2 Wooridul Spine Hospital, Seoul, Korea Objective : Here we describe a microsurgical method for decompression and the radiological findings of the extraforaminal entrapment of the L5 spinal nerve. Methods : The authors reviewed the clinical and neurodiagnostic findings, surgical management, and outcomes in 53 patients with extraforaminal entrapment of L5 who had been successfully decompressed via a microsurgical paramedian tangential approach. A total of 28 women and 25men ranging in age from 54 to 73(mean age 65 years). All patients had uni- or bilateral leg pain due to extraforaminal entrapment of L5 in the lumbosacral spine. The mean follow-up period was 9 months (range 3-15 months). Results : Pain was measured by the Numerical Rating Scale. The function of back was assessed by the Oswestry Disability Index score, and the patient satisfaction was evaluated by the North American Spine Society Outcome Questionnaire. Relief of back pain was obtained for all patients immediately after surgery. The mean Numerical Rating Scale improved from 8.2 before the surgery to 1.7 after the surgery (P< ). The mean ODI score improved from 74.6 before the surgery to 15.3 after the surgery (P< ). Overall, excellent and good result were achieved in 27(51%) and 23(43%) at the last follow-up examination. There was no complications related to the surgery, nor was any spinal instability was detected. The parasagittal T-1 weighted magnetic resonance images showed foraminal stenosis with the circumferential loss of the perineural fat signal at L5-1 level in 23 of 53(43%) patients. Radiological and operating finding showed narrowing of the extraforaminal tunnel that resulted from the annulus bulging in 36 patients(68%), disc protrusion or rupture in 17patients (30%) and osteophytes of the vertebral body in 39 patients(74%). Conclusion : The paramedian tangential approach is a safe, effective procedure that avoids the risk of secondary spinal instability. This study showed that the major causes of the extraforaminal nerve root entrapment in the lumbosacral spine are the bulged annulus, the disc protrusion and osteophytes. The major pathognomonic cause of the extraforaminal L5 nerve entrapment was the bulged annulus fibrosus with the osteophytes. KEY WORDS : Extraforaminal entrapment Lumbosacral spine Paramedian tangential approach Radiculopathy. Introduction It is common to encounter extraforaminal nerve root entrapment in patients with degenerative lumbar disc disease with the use of development of high resolution computed tomography(ct) scan and magnetic resonance imaging(mri). Because of the unique anatomical feature, such as the ala, the iliolumbar ligamentum, and the broad pedicle at the L5-S1 level, L5 root can be frequently compressed in the extraforaminal zone. However, this condition may cause the failure of the back lumbar spine surgery due to the difficulties in making a correct diagnosis before surgery 10,13). Burton et al 3), attributed this phenomenon to the lack of recognition or an inadequate treatment of the lateral canal stenosis. In addition, they considered this condition to be the cause of pain in nearly 60% of patients whose symptoms continued despite surgery. Therefore, the extraforaminal lesion is an important pathologic entity to identify in the patients treated for radiculopathy. The purpose of this study was to describe a microsurgical method for the decompression of the L5 nerve and radiological findings of the extraforaminal entrapment of the L5 spinal nerve. Materials and Methods The authors reviewed the clinical and neurodiagnostic findings, surgical management, and outcomes for 53

2 Extraforaminal Entrapment of L5 patients with extraforaminal entrapment of L5 who were surgically treated via a microsurgical paramedian tangential approach. Patients with the symptomatic spondylolysis, isthmic or degenerative spondylolisthesis showing L5 nerve root compression were excluded from this study. Patients with the multiple level compression including the extraforaminal zone in the lumbosacral spine were also excluded from this study. The diagnosis was established by the combination of radiological tests, CT scans, selective nerve root block and MRI. The selective L5 nerve root block was performed for the purpose of the treatment and diagnosis in all patients. There were 28 women and 25 men who ranged in age from 54 to 73 (mean age 65 years). All patients had uni- or bilateral leg pain due to extraforaminal entrapment of L5 in the lumbosacral spine. The mean follow-up period w- as 9 months (range 3~15 months). Their pain was measured by the Numerical Rating Scale 11), the patients' function was assessed by the Oswestry Disability Index (O- DI) score 5), and the patient satisfaction was evaluated by the North American Spine Society O- utcome Questionnaire using the Patient Satisfaction Index (PSI) that asked, "Would you like to h- ave the same treatment for the same ailment?" The response was graded from 1 to 5 as follows. 1 : definitely not, 2 : probably not, 3 : not sure, 4 : probably yes, and 5 : definitely yes. Responses of 4 or 5 were regarded as the satisfactory outcome 4). Surgical approach The paramedican tangential approach for the extraforaminal decompression was used. The 3-CM longitudinal skin incision was made approximately 3cm lateral to the midline above the dorsal curvature of the ilium in the projection of the disc space (the location was confirmed by needle, lateral x- ray) for the decompression of the foraminal and extraforaminal stenosis. The multifundi and longissimus muscles were identified and dissected away using the fingertips and a pair of scissors. The fingertip was used to identify the base of the transverse process and the lateral aspect of the facet joint. The medial boundary was the lateral edge of the L5-S1 facet joint and the caudal boundary is formed by the upper rim of the sacrum with the costral process. The cranial boundary was the lower edge of the L5 transverse process. Because the surgical field became very deep, the use of a surgical microscope was essential to obtain good surgical vision. The facet joint and the costal process of the sacrum concealed the disc space and the course of the L5 nerve root. A high-speed drill was used to remove the lateral edge of the facet joint and the costal process of the ala to enter the extraforaminal space (Fig. 1). Medial exposure could obtain by removing the lateral margin of the superior facet without compromise of facet joint. During the drilling, care must be taken not to injury the nerve root. The thin layer of inner cortex should be left intact and removed with a dissector to avoid root injury. The iliolumbar ligament maybe found overlying the nerve. Such ligaments could participate in the lateral entrapment of the ganglion or the nerve. The iliolumbar ligament was removed with the punch. The ligament was carefully J Korean Neurosurg Soc 36

3 JS Jang, et al. removed as not to injure the neurovascular bundle and the fat tissue surrounding the L5 root was exposed. Once the d- isc space was palpated, the root w- as protected by a root retractor and additional disc material was removed with pituitary rongeurs and a downbite curette (Fig. 2). The osteophytes from vertebral body beneath the nerve were removed with the down-biting curette, tamp and mallet. Bone fragments were delivered to the disc space, and subsequently removed. The foraminal stenosis was decompressed by the removal of the tip of superior facet. Results The mean Numerical Rating Scale improved from 8.2 before the surgery to 1.7 after the surgery (P< ). The mean ODI score improved from 74.6 before the surgery to 15.3 after the surgery (P< ). Overall, excellent and good results were achieved in 27(51%) and 23(43%) at the last follow-up examination. There were no complications related to the surgery, nor was any spinal instability detected. Operating findings and imagings (MRI and CT scan) were reviewed for all patients. Radiological findings showed a narrowing of the extraforaminal t- unnel that resulted from annulus bulging in 36 patients(68%)(fig. 3), disc protrusion or rupture in 17 patients(30%)(fig. 4) and osteophytes of the vertebral body in 39 patients(74%)(fig. 5). The parasagittal T-1 weighted m- agnetic resonance image showed foraminal stenosis with the circumferential loss of the perineural fat signal at L5-1 level in 23 of 53(43%) patients (Fig. 6). Discussion The extraforaminal L5 root entrapment is common for patients with degenerative lumbar disc diseases. However, it is frequently overlooked as the foraminal or extraforaminal lesion resulting in failed back surgery syndrome 3). Although many clinical studies have reported on the surgical approach for the extraforaminal lesion 1,2,6,14-16,19,20), few studies focused on radiological findings of the extraforaminal entrapment of L5 in the lumbosacral spine on the MRI and CT findings 7,9). Hashimoto et al. described that a MRI of the coronal plane can provide the best anatomical declineation of the lumbosacral nerve root complex related to the adjacent structures 9). However, characteristics of extraforaminal entrapment of L5 on the MRI imaging and CT scan in the standard axial projections need to be established. Several studies reported extraforaminal disc protrusion or rupture may compressed the L5 nerve in the lumbosacral spine 1,2,6,14-16). In this study, for 17 out of 53 patients, the disc herniation caused the narrowing of the extraforaminal tunnel in the lumbosacral spine. The osteophytes on the lower border of the body of L5 and the upper border of the sacrum may contribute to the formation of the inferior portion of the tunnel encasing the nerve 15,17). CT scans should be performed to define and demonstrate the extent of the bony disease. In this study, for 39 out of 53 patients, the osteophytes of the verterbral body caused the narrowing of the extraforaminal tunnel. The diffused b- ulging annulus fibrosus may press the nerve against the sacral ala and

4 Extraforaminal Entrapment of L5 L5 pedicle 2). The diffused annulus bulging was the most frequent cause of narrowing of the extraforaminal tunnel in this study. For 36 out of 53 patients, annulus bulging contributed to the narrowing of extraforaminal tunnel. Based on cadavaric studies, many authors reported that the lumbosacral ligament (LSLs) may compress the L5 spinal nerve and give rise to clinical manifestations 17,18,21). The buckling or the overgrowth of the iliolumbar as well as the lumbosacral ligaments can result in narrowing of the extraforaminal tunnel. The loss of the height of the intervertebral disc, secondary to its desiccation and the degeneration, allows the superior articular process of the inferior vertebra to subluxate anteriorly and superiorly, resulting in the diminished area of the foramen and extraforamen at the lumbosacral spine 8,10). The combination of the disc space narrowing, the overgrowth of the iliolumbar ligament, and the bulging disc and the bony spur may diminish to a great extent the volume of the foramen and extraforamen to a great extent 10). In these cases, the L5 nerve root was compressed at two zones (the foraminal and extraforaminal zone) simultaneously. The parasagittal T- 1 weighted MRI at the L5-S1 foramen showed the circumferential loss of perineural fat signal in 23 out of 53 patients. The size of extraforaminal tunnel in this study was mainly affected by the bulged annulus in 36 patients (68%), the osteophytes of vertebral body in 39 patients (74%) and the disc protrusion in 17 patients (30%). Wiltse's posterior procedures allowed relatively easy access to the extraforaminal zone at the L5-S1 intervertebral level 22). The paramedian tangential approach with the drilling of an osseous triangle (the lateral margin of facet joint and upper rim of the sacrum with the costal process) offers several advantages because the destruction of the facet joint and the manipulation of the dorsal root ganglion (DGR) can be avoided 16). The drilling of the osseous triangle can be extended to the rim of the disc space to gain direct access to the pathologic abnormality, such as osteophytic spurs or a hypertrophic lumbosacral ligament 16). Because of the large anteroposterior diameter of the sacral ala through, which the L5 spinal nerve transverse, the partial resection of the sacral ala along the L5 spinal nerve is done not only in the cephalocaudal direction, but it should also be performed in the anteroposterior direction 12). Because the surgical field becomes very deep, the use of a surgical microscope is essential to obtain the good surgical vision. In summary, the paramedian tangential approach is safe, minimally invasive and provides the complete decompression for this pathologic entity. Our study showed that the major causes of extraforaminal nerve root entrapment in the lumbosacral spine were the bulging annulus fibrosus, the disc protrusion and the osteophytes. In this study, the major pathognomonic cause of the extraforaminal L5 nerve entrapment was the bulged annulus fibrosus with the osteophytes. Conclusion The paramedian tangential approach is a safe, effective procedure that avoids the risk of secondary spinal instability. This study showed that the major causes of the extraforaminal nerve root entrapment in the lumbosacral spine are the bulged annulus, the disc protrusion and osteophytes. The major pathognomonic cause of the extraforaminal L5 nerve entrapment was the bulged annulus fibrosus with the osteophytes. References 1. Abdullah AF, Ditto EW, Byrd EB, Williams R : Extreme lateral lumbar disc herniations. 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