A novel surgical approach to the lumbar spine involving ... · A novel surgical approach to the...

J Neurosurg Spine Volume 24 • May 2016694

techNical NoteJ Neurosurg Spine 24:694–699, 2016

The paravertebral muscles play an important role in the elastic stability and functional movement of the spine. In the conventional posterior surgical ap-

proach to the lumbar spine, the lamina is exposed by strip-ping the paravertebral muscles from the spinous process. Whether the spinous process is resected or preserved, the junction between the detached muscle and bone can-not be restored to its original tight connection. The loss of the normal junction of the paravertebral muscles with the spinous process may be presumed to result in abnor-mal muscle contractions and a decline in muscle support of the spinal column. Moreover, the paravertebral muscles would have already suffered injuries due to direct retrac-tion during surgery.10,11 The paravertebral muscle damage originating from conventional posterior lumbar spine sur-gery can produce muscle atrophy18,26 and decreased muscle strength.7,18 Attempting to reduce invasiveness to the para-

vertebral muscles related to posterior lumbar spine sur-gery, procedures such as spinous process osteotomies,4,29 unilateral laminotomy and bilateral decompression,20,24,30 a tubular retractor system,19,21 spinous process-splitting lami-nectomy28 and muscle-preserving interlaminar decompres-sion3,8,15 have been conceived. The unilateral laminotomy and bilateral decompression for lumbar spinal canal ste-nosis (LSCS) reported by Poletti24 is an excellent proce-dure, allowing preservation of the paravertebral muscles on the nonapproach side. However, on the approach side, the paravertebral muscles are inevitably damaged because of their detachment from the spinous process. In 2002, Shiraishi25 reported an innovative procedure for posterior exposure of the cervical spine in which the spinous pro-cess is longitudinally split on the midline, and the lamina is exposed without stripping the semispinalis cervicis and multifidus muscles from the spinous process.

abbreviatioNS HSS = hemilateral split-off of the spinous process; JOA = Japanese Orthopaedic Association; LSCS = lumbar spinal canal stenosis.Submitted October 25, 2014. accepted May 18, 2015.iNclude wheN citiNg Published online November 6, 2015; DOI: 10.3171/2015.5.SPINE141074.

A novel surgical approach to the lumbar spine involving hemilateral split-off of the spinous process to preserve the multifidus muscle: technical noteKenichi chatani, md

Department of Orthopaedic Surgery, Horikawa Hospital, Kyoto, Japan

In the conventional posterior approach to the lumbar spine, the lamina is exposed by stripping the paravertebral muscles from the spinous process, and the resulting paravertebral muscle damage can produce muscle atrophy and decreased muscle strength. The author developed a novel surgical approach to the lumbar spine in which the attachment of the paravertebral muscles to the spinous process is preserved. In the novel approach, the spinous process is split on the midline without stripping the attached muscles, and a hemilateral half of the spinous process is then resected at the base, exposing only the ipsilateral lamina. Before closing, the resected half is sutured and reattached to the remaining half of the spinous process. Thirty-eight patients with lumbar spinal canal stenosis (LSCS) undergoing unilateral partial laminectomy and bilateral decompression using this novel approach were analyzed. Postoperative changes in the multifi-dus muscle were evaluated by T2 signal intensity on MR images. MRI performed 1 year after the operation revealed no significant difference in the T2 signal intensity of the multifidus muscle between the approach and nonapproach sides. This result indicated that postoperative changes of the multifidus muscle on the approach side were slight. The clinical outcomes of unilateral partial laminectomy and bilateral decompression using this approach for LSCS were satisfactory. The novel approach can be a useful alternative to the conventional posterior lumbar approach.http://thejns.org/doi/abs/10.3171/2015.5.SPINE141074Key wordS minimally invasive surgery; muscle preservation; multifidus muscle; MRI; surgical approach; lumbar spine; technique

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a novel surgical approach to the lumbar spine

J Neurosurg Spine Volume 24 • May 2016 695

Watanabe et al.28 developed a lumbar spinous process-splitting laminectomy in which the lamina is exposed by longitudinally splitting the spinous process while the mus-cular and ligamentous attachments to the spinous process remain intact. They reported that the paravertebral muscle atrophy rate was significantly lower in their procedure than in conventional laminectomy. However, a disadvantage of the procedure is that the force of the multifidus muscle cannot be transmitted to the spinal column because of the separation of the spinous process and the lamina.

In the novel approach reported here, hemilateral split-off of the spinous process (HSS), the spinous process is split on the midline without stripping the attached mus-cles, and then a hemilateral half of the spinous process is resected at the base, exposing only the ipsilateral lamina. Before closing, the resected half is sutured and reattached to the remaining half of the spinous process. The author has used the HSS approach to perform various posterior lumbar spine surgeries. For LSCS, unilateral partial lami-nectomy and bilateral decompression has been performed using the HSS approach.

In the study presented here, the author describes a sur-gical technique using the HSS approach for LSCS and reports postoperative changes in the multifidus muscle evaluated by T2 signal intensity on MR images as well as clinical outcomes.

methodsSurgical technique (hSS approach)

The patient is placed prone on a 4-point frame under general anesthesia. A midline skin incision is made over

the cranial spinous process of the intervertebral level to be decompressed (Fig. 1A). Without detachment of the para-vertebral muscles, the tip of the spinous process is palpat-ed, and the spinous process is longitudinally split on the midline (to a depth of approximately 1.5 cm) using a micro bone saw (Fig. 1B). A hemilateral half of the spinous pro-cess is resected at the base and the resected half with the attached paravertebral muscles is laterally retracted. The rotator muscles terminating in the lamina are resected, and the ipsilateral lamina is exposed (Fig. 1C). Unilateral partial laminectomy and bilateral decompression are per-formed with a surgical microscope (Fig. 1D). Finally, the resected half is reattached to the remaining half of the spi-nous process by ligation with a couple of suture threads (Fig. 1E and F). After surgery, a soft corset is applied to fuse the split spinous process by bone union, and walking is permitted beginning the next day. The corset is used continuously for the first 3 weeks after surgery, and there-after only during the daytime for the next 3 weeks.

patient populationThe study population consisted of 38 patients (22 men

and 16 women) with symptoms of cauda equina com-pression due to LSCS who underwent unilateral partial laminectomy and bilateral decompression using the HSS approach. All surgeries were performed by the same sur-geon. The subjects were consecutive patients who were examined using MRI and CT about 1 year (11–13 months) after surgery. The mean age at the time of the surgery was 71 years (range 54–91 years). Decompression was per-formed at 1 intervertebral level in 27 patients, 2 levels in 9 patients, and 3 levels in 2 patients. Patients with severe

Fig. 1. Illustrations of the HSS approach. a: Skin incision. b: Spinous process split. c: Hemilateral resection of the base of the spinous process. d: Bilateral decompression. e: Ligation of the resected half with the remaining half of the spinous pro-cess. F: Postoperative axial CT scan. Copyright Satoru Nakamura. Published with permission. Figure is available in color online only.


K. chatani


low-back pain due to intervertebral instability were ex-cluded from this study, because intervertebral fusion sur-gery was simultaneously performed. Patients with marked scoliosis were also excluded because of the bilateral dis-crepancy of the multifidus muscle.

evaluation of clinical outcomeClinical outcome measurements were made using the

Japanese Orthopaedic Association Score for Assessment of Treatment for Low Back Pain (JOA score).9 The modi-fied JOA scores (9 points of subjective symptoms and 6 points of clinical signs) were measured preoperatively and 1-year (11–13 months) postoperatively. Postoperative re-covery rates were calculated using the following formula (the Hirabayashi method):

Recovery rate = (postoperative score - preoperative score)/(15 - preoperative score) ×100

A recovery rate of 75% or greater was regarded as excel-lent, 50%–74% as good, 25%–49% as fair, and less than 25% as poor.

Quantitative Analysis of the Multifidus MuscleThe 1.5-T MRI system (Signa, GE) was used to ob-

tain axial T2-weighted MR images (fast spin echo meth-od) about 1 year (11–13 months) after the operation. An analysis of grayscale values (0–256) was performed with image-processing software (ImageJ, version 1.38i; NIH), and the signal intensities of the multifidus muscle were quantified on the axial T2-weighted MR images. For pa-tients who underwent multilevel decompression, the cau-dal decompression level was evaluated. The evaluated levels were L4–5 in 30 patients, L3–4 in 7, and L2–3 in 1. The signal intensities were measured in the most cau-dal scan of the decompression site. Measurement of sig-nal intensity was performed bilaterally, and the multifidus muscle on the nonapproach side (which did not undergo surgical invasion) was used as a control. The regions of interest of the multifidus muscle were established in 3 lay-ers (shallow, middle, deep) to be as large as possible while avoiding large fat masses between muscle layers (Fig. 2). Measurement of signal intensity was performed 3 times in each layer, and the mean value was reported as the signal intensity for each layer. The mean of the signal intensities of the 3 layers was calculated for each side. The difference in the signal intensity of the multifidus muscle between the approach and nonapproach sides was analyzed using the paired t-test. Statistical significance was accepted at p < 0.05.

resultsThe mean operative duration was 111 minutes, and the

mean intraoperative blood loss was 84 g per level. An in-traoperative complication occurred in 1 patient, a dural tear. No neurological deterioration was observed in any patient. Thirty-seven of the 38 patients started to walk the day after surgery, and the remaining patient began 2 days after surgery. No patients required revision surgery for postoperative hematoma or surgical site infection.

The mean preoperative modified JOA score (maximum 15) was 8.9 (range 6–13) and the mean 1-year postopera-tive score was 13.8 (range 10–15). The mean recovery rate was 80% (range 38%–100%); the recovery rate was graded as excellent in 24 patients, good in 12, fair in 2, and poor in none. One-year postoperative CT revealed successful bone union of the split spinous processes in all patients. MRI performed 1 year after the operation showed no marked difference in the shape or size of the multifidus muscle between the approach and nonapproach sides in any patient (Fig. 3). Comparisons of the signal intensity of the multifidus muscle on the axial T2-weighted MR im-ages between the approach and nonapproach sides showed no significant difference (Fig. 4).

discussionVarious procedures have been created to reduce the

paravertebral muscle damage originating from posterior lumbar spine surgery. Kim et al.13 compared the effect of 3 different approaches to the lumbar spinal canal and demonstrated that preservation of the multifidus muscle attachment to the spinous process reduced muscle dam-age. Recently, Liu et al.16 reported an experimental study of the impact of 4 different surgical approaches on the lumbar multifidus muscle and concluded that the multifi-dus muscle could be effectively protected by reducing the extent of muscle detachment and reconstructing the poste-rior bone-tendon complex. Watanabe et al.28 reported that the postoperative multifidus muscle atrophy rate was sig-nificantly lower in spinous process–splitting laminectomy than in conventional laminectomy. However, a disadvan-tage of the spinous process–splitting laminectomy is that the force of the multifidus muscle cannot be transmitted to the spinal column due to separation of the spinous process and the lamina. In the novel HSS approach, only a hemi-lateral half of the spinous process is resected at the base, without stripping the attached muscles. Finally, the resect-ed half is reattached to the remaining half of the spinous process. Consequently, the attachment of the multifidus muscle to the spinous process is preserved, and moreover, the spinous process is anatomically reconstructed by bone union. Although a careful subperiosteal dissection has been performed in the conventional approach, the perios-teum is reattached to the spinous process by scar tissue and the normal attachment of the multifidus muscle to the spinous process cannot be reconstructed.

Fig. 2. Measurement of signal intensity on an axial T2-weighted MR image of the multifidus muscle. Regions of interest were established bilaterally in 3 layers (shallow, middle, deep).




The multifidus muscle consists of several bundles that originate on the spinous process, spread downward and laterally for 2–4 segments, and then attach on the mam-millary processes, iliac crest, and sacrum.2 Surgical inva-sion of the multifidus muscle involves not only the area exposed, but also the caudal area of its course. Therefore, in the present study, to evaluate surgical damage to the multifidus muscle, the signal intensity of the multifidus muscle on MR images was measured in the most caudal scan of the decompression site.

The high signal intensity on T2-weighted MR im-ages of damaged muscle represents denervation and an increase in extracellular fluid,12,23 degeneration and fat infiltration,14,22 incomplete muscle fiber regeneration, and increased extracellular space.6 A less invasive approach results in less change in the T2 signal intensity of the mul-tifidus muscle.5,27 In the present study, the signal intensity on T2-weighted MR images was measured on both ap-proach and nonapproach sides. The multifidus muscle on the nonapproach side, which did not undergo surgical in-vasion, was used as a control, and postoperative changes

of the multifidus muscle on the approach side were evalu-ated by T2 signal intensity. One year after the operation, there was no significant difference in the T2 signal inten-sity of the multifidus muscle between the approach and nonapproach sides. This result indicated that postopera-tive changes of the multifidus muscle on the approach side were slight using the HSS approach.

There are several possible reasons that the HSS ap-proach produces less invasiveness to the multifidus muscle. First, the HSS approach may reduce direct muscle dam-age during surgery because the multifidus muscle is not stripped from the spinous process and retracted through the bone fragment of the split spinous process. Second, the multifidus muscle may maintain its function and avoid dis-use muscle atrophy because the attachment to the spinous process is preserved, and the spinous process is anatomi-cally reconstructed by bone union. Third, when compared with the original unilateral laminotomy and bilateral de-compression procedure,24 in which the spinous process is not resected, the visualization route is closer to the mid-line because of the hemilateral resection of the spinous

Fig. 3. Representative images from patients who underwent the HSS approach. a: Intraoperative photograph. A hemilateral half of the spinous process is resected at the base and the resected half with the attached paravertebral muscles is laterally retracted. Arrows indicate the remaining halves of the spinous process. b and c: Postoperative anteroposterior radiograph (B) and axial CT scan (C). The resected halves are reattached to the remaining halves of the spinous process by ligations. d: One-year postopera-tive axial CT scan. Bone union of the split spinous process is already obtained. e and F: Preoperative (E) and 1-year postopera-tive (F) axial T2-weighted MR images. There was no marked difference in the shape and size of the multifidus muscle before and after the operation. Furthermore, the postoperative image (F) shows no marked difference in the shape and size of the multifidus muscle between the approach (right [Rt]) and nonapproach sides. Figure is available in color online only.


K. chatani


process in the HSS approach. This facilitates exposure of the spinal canal, not only on the approach side, but also on the contralateral side. Consequently, the paravertebral muscles need not be retracted beyond the inferior articu-lar process, and the compression load to the muscles can be reduced. The multifidus muscle is innervated by the medial branch of the posterior ramus of the spinal nerve unisegmentally,17 and injury to this branch results in de-nervation changes in the multifidus muscle bundles. The medial branch of the posterior ramus of the spinal nerve may be injured by excessive lateral retraction of the para-vertebral muscles during surgery. Boelderl et al.1 con-cluded that to prevent injury to the medial branches of the posterior rami of the spinal nerves, the posterior surgical midline approach to the thoracolumbar spine should not be enlarged laterally to the articular processes. In the HSS approach, denervation changes by excessive lateral retrac-tion of the multifidus muscle may be prevented because the paravertebral muscles need not be retracted beyond the inferior articular process.

It has previously been reported that unilateral lami-notomy and bilateral decompression relieve radicular symptoms and claudication of LSCS.20,24,30 The present study shows that unilateral partial laminectomy and bi-lateral decompression using the HSS approach provide similarly excellent outcomes for LSCS. No neurological deterioration and postoperative complications occurred. The operative durations (mean 111 minutes per level) and blood loss (mean 84 g per level) were appropriate. Howev-

er, Palmer et al.21 reported that bilateral decompression of LSCS involving a unilateral approach with a microscope and tubular retractor system could be accomplished with reasonable operative times (mean 90 minutes per level) and with minimal blood loss (mean 26 ml per level). A disadvantage of the HSS approach is bleeding from the cut surface of the split spinous process during surgery. We did not apply bone wax to the cut surface because of its pos-sible adverse effect on postoperative bone healing of the split spinous process. This factor slightly prolonged opera-tive duration, but no patient needed blood transfusion or revision surgery for postoperative hematoma.

conclusionsThe outcomes of unilateral partial laminectomy and

bilateral decompression using the novel HSS approach for LSCS were satisfactory. MRI performed 1 year after the operation revealed no significant difference in the T2 signal intensity of the multifidus muscle between the ap-proach and nonapproach sides. This result is indicative of the damage reduction of the multifidus muscle using the HSS approach, which does not require detachment of the multifidus muscle from the spinous process and does not disturb the function of the multifidus muscle. The HSS approach is a useful method to preserve the multifidus muscle in posterior lumbar spine surgeries.

acknowledgmentThe author thanks Dr. Satoru Nakamura for the illustrations

in Fig. 1.

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Fig. 4. Scatterplot showing signal intensities on axial T2-weighted MR images of the multifidus muscle. Patients (n = 38) who underwent uni-lateral partial laminectomy and bilateral decompression using the HSS approach were assessed 1 year postoperatively. The horizontal axis shows the grayscale values of the T2 signal intensity of the multifidus muscle on the approach side and the longitudinal axis shows them on the nonapproach side. There was no significant difference of the T2 signal intensity between the approach and nonapproach sides.




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disclosureThe author reports no conflict of interest concerning the materi-als or methods used in this study or the findings specified in this paper.

Supplemental informationPrevious PresentationPortions of this work were presented in abstract form as proceed-ings at the 38th Annual Meeting of the Japanese Society for Spine Surgery and Related Research, in Kobe, Japan, April 25, 2009.

correspondenceKenichi Chatani, Department of Orthopaedic Surgery, Horikawa Hospital, 865 Kitahunahashi-cho, Kamigyo-ku, Kyoto 602-0056, Japan. email: [email protected].


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