Departments of 1 Orthopaedic Surgery and 2 Advanced Therapy for Spine and Spinal Cord Disorders, School of Medicine, Keio University, Tokyo, Japan

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1 J Neurosurg Spine 12:72 81, 2010 Posterior decompression surgery for extraforaminal entrapment of the fifth lumbar spinal nerve at the lumbosacral junction Clinical article Mo r i o Ma t s u m o t o, M.D., 1 Ko t a Wa t a n a b e, M.D., 2 Ke n Is h i i, M.D., 1 Ta k a s h i Ts u j i, M.D., 1 Hi r o n a r i Ta k a i s h i, M.D., 1 Ma s a y a Na k a m u r a, M.D., 1 Yo s h i a k i To y a m a, M.D., 1 a n d Ka z u h i r o Ch i b a, M.D. 1 Departments of 1 Orthopaedic Surgery and 2 Advanced Therapy for Spine and Spinal Cord Disorders, School of Medicine, Keio University, Tokyo, Japan Object. In this paper, the authors goal was to elucidate the clinical features and results of decompression surgery for extraforaminal stenosis at the lumbosacral junction. Methods. Twenty-eight patients with severe leg pain caused by extraforaminal stenosis at the lumbosacral junction (18 men and 10 women; mean age 68.2 ± 8.9 years) were treated by posterior decompression without fusion using a microendoscope in 19 patients and a surgical microscope or loupe in 9 patients. The decompression procedures consisted of partial resection of the sacral ala, the L-5 transverse process, and the L5 S1 facet joint along the L-5 spinal nerve. The following items were investigated: 1) preoperative neurological findings; 2) preoperative radiological findings, including plain radiographs, CT scans, selective radiculography of L-5; 3) surgical outcome as evaluated using the Japanese Orthopaedic Association scale for low-back pain (JOA score); and 4) need for revision surgery. Results. All patients presented with neurological deficits compatible with a diagnosis of L-5 radiculopathy such as weakness of the extensor hallucis longus muscle and sensory disturbance in the L-5 area together with neurogenic claudication. On plain radiographs, 21 patients (75%) and 17 patients (60.7%) exhibited lumbar scoliosis ( 5 ) and wedging of the L5 S1 intervertebral space ( 3 ), respectively. The CT scans demonstrated marked osteophyte formation at the posterolateral margin of the L5 S1 vertebral bodies, and a selective L-5 nerve root block was effective in all patients. All patients reported pain relief immediately after surgery. The mean JOA scores were 11.3 ± 3.8 before surgery and 24.3 ± 3.4 at the time of the final follow-up examination; the recovery rate was 68.6 ± 16.5%. The mean estimated blood loss was 66.6 ± 98.6 ml, and the mean surgical time was ± 46.5 minutes. No significant difference in the recovery rate of the JOA scores or in the surgical time and blood loss was observed between the 2 surgical approaches. Four patients underwent revision posterior interbody fusion for the recurrence of radicular pain as a result of intraforaminal stenosis in 3 patients and insufficient decompression of the extraforaminal area in the remaining patient at an average of 19.5 months after surgery. Conclusions. Extraforaminal stenosis at the lumbosacral junction is a rare but distinct pathological condition causing L-5 radiculopathy. Decompression surgery without fusion using a microendoscope or a surgical microscope/ loupe is a feasible and less invasive surgical option for elderly patients with extraforaminal stenosis at the lumbosacral junction. (DOI: / SPINE09344) Ke y Wo r d s extraforaminal stenosis posterior decompression sacral ala lumbosacral tunnel failed back surgery Ex t r a f o r a m i n a l stenosis at the lumbosacral junction can affect the L-5 nerve root causing sciatic pain, motor loss, and sensory disturbance at the L-5 region, as well as neurogenic claudication. 9,10 This pathological condition is much rarer than intraspinal canal Abbreviations used in this paper: EBL = estimated blood loss; JOA = Japanese Orthopaedic Association; NSAID = nonsteroidal antiinflammatory drug; VB = vertebral body. lesions, making the diagnosis difficult. Extraforaminal stenosis at the lumbosacral junction was first reported by Danforth and Wilson, 3 who observed compression of the L-5 spinal nerve by osteophytes at the lateral margin of the L-5 and S-1 VBs and the ligaments at the lumbosacral junction in cadaveric specimens. Wiltse et al. 19 This article contains some figures that are displayed in color on line but in black and white in the print edition. 72 J Neurosurg: Spine / Volume 12 / January 2010

2 Decompression surgery for extraforaminal stenosis reported cases of far-out syndrome, which was caused by pinching of the lumbar spinal nerve between the transverse process of the L-5 vertebra and the sacral ala. According to their report, far-out syndrome was typically observed in elderly patients with degenerative scoliosis and/or wedging of the L5 S1 disc space, or in patients with spondylolytic spondylolisthesis with a percentage of slippage of more than 20%. Nathan et al. 13 conducted a cadaveric study and found that the L-5 VB, the lumbosacral ligament, and the sacral ala formed the lumbosacral tunnel, where the L-5 spinal nerve passes and could be entrapped. We also conducted a cadaveric study to clarify the relation between the osteophytes of the L5 S1 VBs and the L-5 spinal nerve, and found that specimens with osteophytes were more often associated with stenosis of the lumbosacral tunnel than those without osteophytes. 10 Thus, extraforaminal stenosis at the lumbosacral junction may not be identical to the well-known far-out syndrome proposed by Wiltse et al.; instead, it likely encompasses a wide spectrum of compressive lesions caused by osteophytes at the L5 S1 VBs, L-5 transverse process, sacral ala, and lumbosacral ligament. 1,10,13,14,17 Surgical intervention should be considered for patients with severe L-5 radiculopathy that does not respond to conservative therapy including the use of NSAIDs, a selective nerve root block, and a brace. However, the optimal surgical method for lumbosacral extraforaminal stenosis has not been established. Because this disease mostly affects the elderly, the surgery should be as minimally invasive as possible. Therefore, we have treated patients with extraforaminal stenosis at the lumbosacral junction by posterior decompression surgery without fusion. For this procedure, we have adopted a microendoscope or a surgical microscope or loupe to minimize the damage to the posterior lumbar structures and to optimize the visualization of the surgical field, which is located laterally and deeply at the lumbosacral junction. 9,10 The purpose of this study was to elucidate the clinical features of extraforaminal stenosis at the lumbosacral junction and the surgical outcomes and limitations of posterior decompression without fusion for this relatively uncommon disease. Methods Twenty-eight patients (18 men and 10 women; mean age at time of surgery 68.2 ± 8.9 years, range years) with extraforaminal stenosis at the lumbosacral junction were treated by posterior decompression alone as the index surgery at Keio University Hospital or at affiliated hospitals in Tokyo, Japan. The mean follow-up period was 32.5 ± 20.7 months (range months) (Table 1). All patients had severe leg pain that did not respond to conservative treatments, such as NSAIDs, epidural steroid injection, or selective nerve root block. Nine patients (32.1%) had a history of previous lumbar surgery including posterior decompression of the spinal canal in 7 patients, anterior lumbar interbody fusion at L4 5 in 1 patient, and percutaneous laser discectomy at L4 5 in 1 patient. Five of these patients had no or only slight improvement after their previous surgeries, while J Neurosurg: Spine / Volume 12 / January 2010 the remaining 4 patients reported substantial pain relief. The mean time period between the previous surgery and the index surgery was 30.8 ± 46.0 months (range months). A diagnosis of extraforaminal stenosis at the lumbosacral junction was established in each patient based on the results of both neurological and radiological examinations. As part of the radiological examination, all patients underwent plain radiography, MR imaging, myelography, and CT imaging; selective L-5 radiculography and a subsequent nerve root block were also performed. Surgical Procedures Posterior decompression was performed under a surgical microscope/loupe in 9 patients and using a microendoscope in 19 patients. The surgical microscope/loupes were used for patients treated during the early period of this study. In addition to decompression of the extraforaminal lesions, 2 patients also underwent intraspinal canal decompression along the L-5 nerve root at the L4 5 level because the possibility of intraspinal canal lesions could not be excluded prior to the index surgery. However, no apparent nerve root compression was observed in the spinal canal in either case during the surgery. The surgical procedures have been described previously. 9 Briefly, the patient was placed prone on a Hall frame. When using a microscope/surgical loupe, a skin incision of 5 cm was made ~ 3 4 cm lateral to the spinous processes, and the extraforaminal zone (L-5 transverse process, sacral ala, and lateral margin of the L5 S1 facet) was exposed via the intermuscular approach proposed by Wiltse et al. 20 After exposure of the extraforaminal region, the muscles attached to the L-5 transverse process, the lateral aspect of the L5 S1 facet, and the sacral ala were dissected and removed using pituitary rongeurs. Because the space between the sacral ala and L-5 transverse process is usually very narrow, mobilization of L-5 using a towel clip or an up-angled curette hooked onto a bony structure of L-5 facilitated identification of the space between the L-5 transverse process and the sacral ala. The inferior aspect of the proximal third of the L-5 transverse process, the lateral edge of the L5 S1 facet joint, and the superior-medial portion of the sacral ala were resected using a high-speed drill, Kerrison rongeurs, and curettes (Fig. 1 left). After the resection of the longitudinal fibers of the iliolumbar ligament attached to the L-5 transverse process, the L-5 spinal nerve was usually identified at the extraforaminal zone by dissecting the overlying fat tissue. Further decompression by partial resection of the sacral ala was performed along the nerve laterally and caudally (Fig. 1 right). Decompression was completed when the L-5 spinal nerve was released from the surrounding bony and ligamentous structures, as confirmed using microdissectors. No attempt was made to remove the osteophytes of the VBs or to dissect the lumbosacral ligament, as this is technically demanding and can damage vascular structures in the retroperitoneal space. When a microendoscope was used, the point for the skin incision, located just inferior to the L-5 pedicle and just lateral to the L5 S1 facet joint, was determined under an image intensifier. An approximately 1.6- to 2-cm 73

3 M. Matsumoto et al. TABLE 1: Patient demographics and neurological findings* Case No. Age (yrs), Sex Previous Op Previous Op Effective? Laterality SLR Kemp Sign L 5 Sensory Disturb EHL Weakness 1 56, M none no rt , F none no lt , F L4 5 decompression yes lt , M L4 5 decompression no rt , F none no lt , M none no rt , M none no lt , M none no rt , M none no lt , F none no rt , M L4 5 decompression yes rt , M L4 5 decompression no lt , M L4 5 decompression no lt , F none no rt , F none no rt , F none no lt , M none no lt , M L4 5 laser no lt , M none no lt , M none no lt , M L4 5 ALIF yes lt , F none no lt , M none no lt , M L2 5 decompression yes rt , M L4 5 decompression no lt , F none no lt , M none no rt , F none no lt NC (m) * ALIF = anterior lumbar interbody fusion; Disturb = disturbance; EHL = extensor hallucis longus; NC = neurogenic claudication (maximum walking distance); SLR = straight leg raising test; + = present; = absent. skin incision was made across the previously determined point. The METRx MED system (Medtronic Sofamor Danek) was used for the entire procedure. After dilation of the paravertebral muscles, a tubular retractor with a diameter of 1.6 cm was docked on the inferior part of the L-5 transverse process. An endoscope was set on the tubular retractor, and decompression was conducted in the same manner as described above. Regardless of the surgical method, the patients were encouraged to stand up and walk on the day after surgery. Preoperative and Postoperative Evaluations The following items were investigated: 1) preoperative neurological findings; 2) preoperative radiological findings, including plain radiographs, CT scans, and selective L-5 radiculography; 3) surgical outcomes evaluated using the JOA score for low-back pain (Table 2); and 4) the need for revision surgery. On plain radiographs, the presence or absence of degenerative lumbar scoliosis, the curve and magnitude of the Cobb angle, and the convexity of the curve and tilting angle of L-5 against the sacrum (the angle between the line tangential to the upper end of the L-5 VB and the line connecting the tops of the bilateral sacral ala; see Fig. 2) were evaluated. Results Neurological Findings Neurological deficits detected on physical examination varied in each patient (Table 1). However, the majority of patients demonstrated motor and/or sensory deficits in the unilateral L-5 region that were compatible with L-5 radiculopathy. A straight leg raising test (30 70 ) was positive in 8 patients (28.6%). The Kemp sign was positive in 22 patients (78.6%). Weakness of the exten- 74 J Neurosurg: Spine / Volume 12 / January 2010

4 Decompression surgery for extraforaminal stenosis Fig. 1. Schematic drawings of the area to be decompressed. Left: The fifth spinal nerve runs through the lumbosacral tunnel, which consists of the lumbosacral ligament, the sacral ala, and the L5 VB. Decompression of the nerve can be achieved by partial resection of the sacral ala, the lateral part of the L5 S1 facet joint, and the inferior part of the L-5 transverse process (dotted line). Right: After decompression. sor hallucis longus muscle was observed in 23 patients (82.1%), and sensory disturbance (light touch and pinprick) in the L-5 area was seen in 25 patients (89.3%). All patients complained of neurogenic claudication (nonstop walking distances shorter than 500 m in 8 patients and shorter than 100 m in 20 patients). The laterality of the symptoms was left in 18 patients (64.3%) and right in 10 patients (35.7%). Radiological Findings Plain Radiographs. Degenerative lumbar scoliosis (Cobb angle 5 ) was observed in 21 patients (75%; Table 3). The mean Cobb angle was 12.3 ± 5.5 (range 5 21 ). The convexity of the curve was to the right in 10 patients and to the left in 11. The sides of convexity and the patients symptoms were the same in 16 patients (76.2%) and opposite in 5 patients. Wedging of the L5 S1 intervertebral space (tilting angle 3 ) was observed in 17 patients (60.7%). The mean tilting angle was 5.9 ± 1.9 (range 3 9 ). The side of tilting and the patients symptoms were the same in 16 patients (94.1%) and opposite in 1. Anterior and posterior slippage of L-5 was observed in 3 (mean slippage distance 3.0 mm) and 3 (4.3 mm) patients, respectively. Magnetic Resonance and CT Images. Prominent osteophyte formation at the posterolateral margin of the L5 S1 VBs was noted on the symptomatic side in all patients (Figs. 3 and 4A). On MR images and myelograms, central spinal canal stenosis was not evident in any patient (Fig. 4A and B). However, moderate stenosis at the lateral recess of L4 5 was observed in 2 patients, and the simultaneous decompression of the lateral recess of L4 5 was conducted in addition to extraforaminal decompression in these 2 patients. The intervertebral disc at L5 S1 was highly degenerated in all patients (Fig. 4B). J Neurosurg: Spine / Volume 12 / January 2010 Selective Radiculography. Selective radiculography demonstrated a narrowing of iodine contrast around the L-5 spinal nerve in the extraforaminal area (Fig. 4C), and a nerve root block with steroids and local anesthetics immediately, but temporarily, relieved radicular pain in all patients. Surgical Outcomes All patients reported relief of their preoperative symptoms after surgery by the time of discharge from the hospital (mean 11.4 days after surgery) (Fig. 4D and E), although 4 patients had later recurrence of symptoms. The mean JOA scores were 11.3 ± 3.8 before surgery and 24.3 ± 3.4 at the final follow-up, and the mean recovery rate was 68.6 ± 16.5% (Table 4). No significant differences in the pre- or postoperative JOA scores or the recovery rate were observed between the patients who underwent the two different surgical approaches (microendoscope vs microscope/loupe) (Table 5). Postoperative CT scans were obtained in 24 of 28 patients, revealing that adequate decompression of the extraforaminal area (the upper part of the sacral ala from the posterior to the anterior margin) had been achieved in 23 patients (Fig. 4F), but not in a patient who underwent revision surgery due to inadequate decompression. The mean EBL was 66.6 ± 98.6 ml, and the mean surgical time was ± 46.5 minutes. Again, no significant differences in these parameters were observed between the surgical groups. No serious complications occurred in any of the patients. However, in 4 patients treated using a microendoscope and 1 patient treated using a loupe, the blood loss exceeded 100 ml. This relatively large amount of blood loss was caused by difficulty in controlling the bleeding from the vessels around the fifth spinal nerve as well as a lengthy surgical time. 75

5 M. Matsumoto et al. TABLE 2: The JOA scoring system for low-back pain* Definition & Description Score subjective symptoms (9 points) low-back pain none 3 occasional mild pain 2 frequent mild or occasional severe pain 1 frequent or continuous severe pain 0 leg pain &/or tingling none 3 occasional mild pain 2 frequent mild or occasional severe pain 1 frequent or continuous severe pain 0 gait normal 3 ab le to walk > 500 m, w/ pain, tingling, &/or muscle 2 weakness un able to walk > 500 m, due to leg pain, tingling, &/or 1 muscle weakness un able to walk > 100 m, due to leg pain, tingling, &/or 0 muscle weakness clinical signs (6 points) straight leg raising test (including tight hamstring) normal <30 0 sensory disturbance none 2 slight disturbance 1 marked disturbance 0 motor disturbance (MMT) none (Grade 5) 2 slight weakness (Grade 4) 1 marked weakness (Grades 3 0) 0 restriction of ADLs (14 points) ADL turning over while lying down 0 2 standing 0 2 washing face 0 2 leaning forward 0 2 sitting (1 hr) 0 2 lifting or holding 0 2 walking 0 2 urinary bladder function ( 6 points) normal 0 mild dysuria 3 severe dysuria 6 * ADL = activities of daily living; MMT = manual muscle testing. A score of 0 indicates a severe restriction; a score of 1, moderate restriction; and a score of 2, no restriction. Fig. 2. Case 1. Anteroposterior radiograph obtained in a 56-year-old man with right leg pain showing lumbar scoliosis (Cobb angle 19.8 ; right convex; L-5 tilted 9.8 toward the right). Revision Surgery Four patients underwent revision surgery for the recurrence of radicular pain at an average of 19.5 months after the index surgery (range months). One of the 4 patients (Case 21) had undergone anterior interbody fusion at L4 5 prior to the decompression surgery. Posterior interbody fusion was performed at L3 S1 in 1 patient and at L5 S1 in 3 patients. Although there was no significant difference between the 4 patients with revision surgery and those without in the preoperative Cobb angle (11.03 ± 6.57 vs ± 6.66 ) or L5 S1 tilting angle (5.20 ± 3.57 vs 4.17 ± 2.98 ), the L5 S1 tilting angle tended to be larger in the former. The 3D CT scans obtained in the 4 patients before the revision surgery revealed narrowing of the foramen in 3 patients and residual stenosis in the caudal level of the sacral ala in 1 patient. During the revision surgery, compression of the L-5 nerve root ganglia in the neural foramen at L5 S1 was observed in 3 patients, and 1 patient without any signs of foraminal stenosis and with a history of anterior interbody fusion at L4 5 was considered to have residual stenosis of the extraforaminal region as a result of insufficient decompression during the index surgery. All the 76 J Neurosurg: Spine / Volume 12 / January 2010

6 Decompression surgery for extraforaminal stenosis TABLE 3: Radiographic findings* Case No. Scoliosis ( ) Convex Side L5 S1 Wedging ( ) Closing Side Slippage (mm) rt 9.2 rt rt 7.0 rt rt 8.0 rt rt < lt 3.0 lt rt 5.8 rt lt 3.7 lt rt 1.6 rt rt < <5 < <5 rt 3.0 rt lt 5.7 lt rt < lt 8.8 lt rt 8.3 rt 0 16 <5 < <5 < lt 5.4 lt lt 6.3 lt lt 5.0 lt 0 21 <5 < <5 < lt 4.0 lt rt 5.5 rt lt < lt 5.0 lt 0 27 <5 < lt 6.4 lt 0 * = not possible to determine because of small size of angle. A negative value indicates posterior slippage. patients reported the relief of radicular pain after revision surgery. J Neurosurg: Spine / Volume 12 / January 2010 Discussion Extraforaminal stenosis at the lumbosacral junction is a rare but distinct pathological condition causing L-5 radiculopathy. This disease is often overlooked because of the difficulty in establishing the diagnosis and often results in failed back surgery syndrome. In fact, 5 patients in this series had undergone decompression surgery at L4 5 without attaining any improvement in their symptoms. The diagnosis of this disease is difficult to establish based on a single diagnostic modality and requires comprehensive clinical and radiological information, as follows: 1) Clinically, patients with this disease present with unilateral severe leg pain and neurogenic claudication. 2) Neurologically, patients demonstrate deficits in the L-5 nerve distribution including weakness in the extensor hallucis longus muscle and sensory disturbance. Most patients show a positive Kemp sign, which is attributable to a narrowing of the extraforaminal area by forced dorsolateral extension of the lower back. 3) Radiologically, on plain radiographs, the majority of patients exhibit mild to moderate degenerative lumbar scoliosis, the curve convexity of which is identical to the symptomatic side; wedging of the L5 S1 intervertebral space is also frequently noted, and L-5 tilts toward the symptomatic side; MR imaging demonstrates little, if any, abnormality in the intraspinal canal at L4 5 or L5 S1 but may reveal a severely degenerated disc at L5 S1; CT scans show prominent osteophytes at the posterolateral borders of the L-5 and S-1 VBs; compression of the L-5 spinal nerve between these osteophytes and the sacral ala can be observed using selective radiculography. Furthermore, the diagnosis can be confirmed by the temporary relief of pain after a selective L-5 nerve root block. Although surgical cases of far-lateral disc herniation at the lumbosacral junction have been reported by many authors, 2,6,12,15,16 the optimal surgical option for extraforaminal stenosis has yet to be established. Surgical options for extraforaminal stenosis at the lumbosacral 77

7 M. Matsumoto et al. Fig. 3. A CT scan at the level of L5 S1 showing an osteophyte at the posterolateral margin of the L5 S1 VBs (arrow). junction include direct removal of the osteophytes via an anterior approach 4,10 and posterior decompression with or without fusion. In this study, we investigated the surgical results of posterior decompression alone using a microendoscope or surgical microscope or loupe, all of which may be a less invasive treatment for this disease. Posterior decompression alone improved radicular pain in all patients at least for a while after surgery, although the symptoms recurred in 4 patients. The recovery rate of the JOA score (68.6%) was comparable to that for lumbar spinal canal stenosis, as previously reported by others (48 69%). 7,18,21 Thus, posterior decompression without fusion may be a feasible surgical option for elderly patients suffering from extraforaminal stenosis. The use of a microendoscope or a surgical microscope/loupe facilitated visualization of the surgical field and avoided substantial damage to the posterior musculature, thereby making the surgery less invasive. No significant differences in the clinical results, surgical time, or blood loss were observed between the Fig. 4. Case 10. Images obtained in a 78-year-old woman who presented with severe right leg pain. A: A CT scan obtained at L5 S1 showing a prominent osteophyte on the right (arrows), but no stenosis in the central spinal canal. B: Sagittal T2-weighted MR image showing a lack of central spinal canal stenosis at either L4 5 or L5 S1, but severe disc degeneration at L5 S1 is observed. C: Selective radiculography of the L-5 spinal nerve demonstrating a pinched L-5 spinal nerve between the inferolateral border of the L-5 VB and the sacral ala (arrow). Immediate pain relief was obtained after the injection of local anesthetics and steroids. D: Intraoperative photograph taken using the microendoscope, showing a good decompression of the L-5 spinal nerve (arrows) after resection of part of the right L-5 transverse process (T), the L5 S1 facet joint (F), and the sacral ala (S). E: Postoperative 3D CT reconstruction showing the area of decompression (arrows). F: Cross-sectional CT scan obtained at the L5 S1 level, showing partial resection of the right sacral ala. 78 J Neurosurg: Spine / Volume 12 / January 2010

8 Decompression surgery for extraforaminal stenosis TABLE 4: Surgical methods and outcomes* Case No. JOA Score Method Preop Postop Recovery Rate (%) Surgical Time (min) EBL (ml) Revision Op (time btwn ops) 1 microendoscope PLIF L4 S1 (14 mos) 2 microendoscope microendoscope microendoscope PLIF L5 S1 (26 mos) 5 microendoscope microendoscope microendoscope PLIF L5 S1 (25 mos) 8 microendoscope microendoscope microendoscope microendoscope microendoscope microendoscope microendoscope microendoscope microendoscope microendoscope microendoscope microendoscope op microscope op microscope PLIF L5 S1 (13 mos) 22 op microscope op microscope loupe loupe loupe loupe loupe ± ± ± ± ± 98.6 * PLIF = posterior lumbar interbody fusion. 2 surgical procedures. Thus, surgeons may choose either of these approaches, depending on their experience and preference. Problems associated with posterior decompression without fusion include the recurrence of symptoms (14.3% in this series), the lengthy surgical time, and occasionally a significant amount of blood loss. The recurrence of symptoms is mainly attributable to foraminal stenosis. It is usually difficult to differentiate intraforaminal, extraforaminal, and combined intra- and extraforaminal stenosis before surgery, because patients with any of these 3 types of stenosis present with the same symptoms, that is, L-5 radiculopathy, and because radiological examinations often fail to demonstrate intraforaminal stenosis. In patients who are suspected of having intraforaminal stenosis, transforaminal or posterior interbody fusion with thorough decompression of the L5 S1 neural foramen may be the treatment of choice. Three patients in the J Neurosurg: Spine / Volume 12 / January 2010 present series experienced recurrence within a relatively short time after extraforaminal decompression due to intraforaminal stenosis detected at the time of the revision surgery. Because the L5 S1 tilting angle tended to be larger in the patients who underwent revision, those with large L5 S1 wedging may better be excluded from the decompression-alone surgery. The definite threshold of the tilting angle for avoidance of revision surgery needs to be determined by a further study in a larger number of patients. A preoperative diagnostic tool to elucidate intraforaminal stenosis is needed. Two useful diagnostic modalities for investigating intraforaminal lesions might be 3D CT scans and coronal MR imaging (Fig. 5); however, once again, further study is necessary to confirm the efficacy of such radiological modalities. The lengthy surgical time and the occasional large amount of blood loss can be attributed to the technical complexity of this surgery. The use of a microendoscope, 79

9 M. Matsumoto et al. Table 5: Comparison between microendoscope and microscope/loupe Parameter Microendoscope Microscope/Loupe p Value preop JOA score 10.7 ± ± postop JOA score 22.8 ± ± recovery rate (%) 67.3 ± ± op time (min) ± ± EBL (ml) 75.8 ± ± in particular, is reported to have a steep learning curve. 5,8,11 The surgical field during extraforaminal decompression is so deep that surgeons must take their time to avoid becoming disoriented. Bleeding from the vessels around the L-5 spinal nerve is sometimes too intense to control. Adequate use of hemostats and a bipolar coagulator as well as efforts to shorten the surgical time are necessary for reducing the amount of blood loss. Conclusions Decompression surgery without fusion is a feasible and less invasive surgical option for elderly patients with extraforaminal stenosis at the lumbosacral junction. Disclosure Morio Matsumoto is a consultant of Medtronic Sofamor Danek, Japan, advising for the development of spine devices and receiving a consultation fee of less than $10,000 per year. References 1. Briggs CA, Chandraraj S: Variations in the lumbosacral ligament and associated changes in the lumbosacral region resulting in compression of the fifth dorsal root ganglion and spinal nerve. Clin Anat 8: , Cervellini P, De Luca GP, Mazzetto M, Colombo F: Micro-endoscopic-discectomy (MED) for far lateral disc herniation in the lumbar spine. Technical note. Acta Neurochir Suppl 92: , Danforth MS, Wilson PD: The anatomy of the lumbosacral region in relation to sciatic pain. J Bone Joint Surg Am 7: , Dezawa A, Yamane T, Mikami H, Miki H: Retroperitoneal laparoscopic lateral approach to the lumbar spine: a new approach, technique, and clinical trial. J Spinal Disord 13: , Foley KT, Smith MM: Microendoscopic discectomy. Tech Neurosurg 3: , Jane JA, Haworth CS, Broaddus WC, Lee JH, Malik J: A neurosurgical approach to far-lateral disc herniation. Technical note. J Neurosurg 72: , Kawaguchi Y, Kanamori M, Ishihara H, Kikkawa T, Matsui H, Tsuji H, et al: Clinical and radiographic results of expansive lumbar laminoplasty in patients with spinal stenosis. J Bone Joint Surg Am 87: , Khoo LT, Fessler TG: Microendoscopic decompressive laminotomy for the treatment of lumbar stenosis. Neurosurgery 51: S146 S154, Matsumoto M, Chiba K, Ishii K, Watanabe K, Nakamura M, Toyama Y: Microendoscopic partial resection of the sacral ala to relieve extraforaminal entrapment of the L-5 spinal nerve at the lumbosacral tunnel. Technical note. J Neurosurg Spine 4: , Matsumoto M, Chiba K, Nojiri K, Ishikawa M, Toyama Y, Nishikawa Y: Extraforaminal entrapment of the fifth lumbar spinal nerve by osteophytes of the lumbosacral spine: anatomic study and a report of four cases. Spine (Phila Pa 1976) 27: E169 E173, Matsumoto M, Watanabe K, Tsuji T, Ishii K, Takaishi H, Nakamura M, et al: Microendoscopic discectomy for lumbar disc herniation with bony fragment due to apophyseal separation. Minim Invasive Neurosurg 50: , Muller A, Reulen HJ: A paramedian tangential approach to lumbosacral extraforaminal disc herniations. Neurosurgery 43: , Nathan H, Weizenbluth M, Halperin N: The lumbosacral ligament (LSL) with special emphasis on the lumbosacral tunnel and the entrapment of the 5th lumbar nerve. Int Orthop 6: , 1982 Fig. 5. Case 1. A Three-dimensional CT scans obtained before revision surgery (A and B) and a postoperative radiograph (B and C) obtained in a 56-year-old man who experienced symptom recurrence and underwent revision surgery by posterior lumbar interbody fusion. 80 J Neurosurg: Spine / Volume 12 / January 2010

10 Decompression surgery for extraforaminal stenosis 14. Olsewski JM, Simmons EH, Kallen FC, Mendel FC: Evidence from cadavers suggestive of entrapment of fifth lumbar spinal nerves by lumbosacral ligaments. Spine (Phila Pa 1976) 16: , O Toole JE, Eichholz KM, Fessler RG: Minimally invasive far lateral microendoscopic discectomy for extraforaminal disc herniation at the lumbosacral junction: cadaveric dissection and technical case report. Spine J 7: , Reulen HJ, Müller A, Ebeling U: Microsurgical anatomy of the lateral approach to extraforaminal lumbar disc herniations. Neurosurgery 39: , Transfeldt EE, Robertson D, Bradford DS: Ligaments of the lumbosacral spine and their role in possible extraforaminal spinal nerve entrapment and tethering. J Spinal Disord 6: , Watanabe K, Hosoya T, Shiraishi T, Matsumoto M, Chiba K, Toyama Y: Lumbar spinous process-splitting laminectomy for lumbar canal stenosis. Technical note. J Neurosurg Spine 3: , Wiltse LL, Guyer RD, Spencer CW, Glenn WV, Porter IS: Alar transverse process impingement of the L5 spinal nerve: the far-out syndrome. Spine (Phila Pa 1976) 9:31 41, Wiltse LL, Spencer CW: New uses and refinements of the paraspinal approach to the lumbar spine. Spine (Phila Pa 1976) 13: , Xia Y, Ishii K, Matsumoto M, Nakamura M, Toyama Y, Chiba K: Radiographic predictors of residual low back pain after laminectomy for lumbar spinal canal stenosis: minimum 5-year follow-up. J Spinal Disord Tech 21: , 2008 Manuscript submitted April 17, Accepted July 29, Portions of this work were presented in abstract form at the 7th Pacific and Asian Society of Minimally Invasive Spine Surgery, Gyeongju, Korea, Address correspondence to: Morio Matsumoto, M.D., Department of Orthopaedic Surgery, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo, , Japan. morio@sc.itc.keio.ac.jp. J Neurosurg: Spine / Volume 12 / January