Eur Spine J DOI 10.1007/s00586-013-3116-7
ORIGINAL ARTICLE
Spinal canal morphology and clinical outcomes of microsurgical bilateral decompression via a unilateral approach for lumbar spinal canal stenosis Won-Seok Choi • Chang Hyun Oh • Gyu Yeul Ji • Sung Chan Shin • Jang-Bo Lee Dong-Hyuk Park • Tai-Hyoung Cho
•
Received: 7 August 2013 / Revised: 12 November 2013 / Accepted: 14 November 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract Purpose Microsurgical bilateral decompression via a unilateral approach for lumbar spinal stenosis is a less invasive technique compared to conventional laminectomy. Although many technical reports have demonstrated acceptable overall surgical outcomes for this approach, no studies have attempted to clarify the clinical outcomes thereof in regard to anatomical variance of the spinal canal. This study was conducted to analyze the clinical outcomes of microsurgical bilateral decompression via a unilateral approach according to spinal canal morphology in degenerative lumbar spinal stenosis. Methods Between January 2008 and December 2009, 144 patients with single-level spinal lumbar stenosis underwent microsurgical bilateral decompression via a unilateral approach by a single surgeon. Patients were categorized into three groups according to spinal canal shape: round
W.-S. Choi and C. H. Oh contributed equally to this project and should be considered co-first authors. W.-S. Choi C. H. Oh Department of Neurosurgery, Spine and Joint Research Institute, Guro Teun Teun Hospital, Seoul, Republic of Korea G. Y. Ji Department of Neurosurgery, Yonsei University College of Medicine, Seoul, Republic of Korea S. C. Shin Department of Neurosurgery, Jangan-dong Teun Teun Hospital, Seoul, Republic of Korea J.-B. Lee D.-H. Park T.-H. Cho (&) Department of Neurosurgery, Korea University Anam Hospital, Korea University College of Medicine, 126-1, 5-ga, Anam-dong, Seongbuk-gu, Seoul 136-705, Republic of Korea e-mail: [email protected]
(n = 42), oval (n = 36), and trefoil (n = 66), and clinical parameters were assessed both before and after surgery with 2–3 years of follow-up. Results Mean visual analog scale (VAS) and Oswestry disability index (ODI) decreased after surgery, respectively, from 8.1 and 59.8 % to 2.1 and 19.1 % in the round shaped spinal canal group, from 7.2 and 47.1 % to 2.2 and 15.1 % in the oval shaped spinal canal group, and from 6.8 and 53.6 % to 3.6 and 33.3 % in the trefoil shaped spinal canal group. In all groups, VAS and ODI scores significantly improved postoperatively (p \ 0.01), although less improved VAS and ODI scores were observed in the trefoil shaped spinal canal group (p \ 0.01). The overall patient satisfaction rate was 66.7 %; however, statistically significant lower satisfaction rates were reported in the trefoil shaped spinal canal group (p \ 0.01). Conclusions Microsurgical bilateral decompression via a unilateral approach may be a good modality for treating round or oval shape spinal canal stenosis, but is not recommended for trefoil-shaped-stenosis. The current authors recommend performing the bilateral decompression technique in cases of trefoil-shaped-spinal canal stenosis. Keywords Microsurgical bilateral decompression Unilateral approach Spinal canal stenosis Clinical result
Introduction Lumbar spinal stenosis is a common disease treated by spinal surgery. The traditional treatment of spinal stenosis involves performing a wide laminectomy with sufficient decompression and undercutting of the medial facet with a foraminotomy [1–3]. To alleviate spinal instability
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Eur Spine J Table 1 Spinal canal stenosis shapes according to spinal level Level
Spinal canal stenosis shape Round
Oval
Trefoil
Total
L2/3
0
6
0a
6
L3/4
6
12
0a
18
L4/5
24
18
42
84
L5/S1
12
0
24
36
Total
42
36
66
144
a
There were no cases of trefoil shaped spinal canal stenosis at levels L2/3 and L3/4
following a conventional laminectomy, which may cause deterioration of symptoms, less invasive decompressive procedures such as microsurgical bilateral decompression via a unilateral approach (MBDU) have been introduced for the treatment of spinal stenosis [4–8]. As bilateral decompression via a unilateral approach requires the performance of an unroofing technique, anatomical variance of the spinal canal could be an important factor for applying MBDU for lumbar spinal stenosis. However, to our knowledge, none have reported on the clinical outcomes of MBDU in regard to anatomical variance of the spinal canal. We, therefore, attempted to assess the clinical outcomes of MBDU according to the shape of spinal canal stenosis with a minimum of 2 years follow-up.
Materials and methods Patient population This retrospective analysis study was conducted at a single institution between January 2008 and December 2009 after gaining approval from the Teun Teun institutional review board. One hundred forty-four subjects with single-level spinal lumbar stenosis underwent MBDU by a single surgeon on an established evaluation and follow-up protocol. The mean age of the patients was 64 years (range from 47 to 79 years), and 78 patients were male. We retrospectively reviewed office charts, hospital charts, and radiologic studies to assess preoperative symptomatology, findings on clinical examinations, and radiologic characteristics. All cases were administered conservative care for at least 2 months, and cases who demonstrated limited benefit from conservative treatment were selected as candidates for this technique. The inclusion criteria for patients were a presence of single-level spinal lumbar stenosis, chronic and persistent radiculopathy despite conservative treatment, progressive neurologic deficits, persistent and unremitting lower back pain for more than 3 months, loss of quality of life because
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of neurological claudication, and a minimum follow-up period of 2 years. The exclusion criteria for the patients were previous spine surgery, a compression fracture or instability at the segments including degenerative spondylolisthesis, and patients who underwent simultaneous decompression at adjacent segments. Type of spinal canal stenosis We performed radiologic assessments preoperatively. Radiographic assessments were made by two different independent observers including the treating surgeon. Preoperative computed tomography (CT) images were evaluated to assess the interpedicular distance and the anteroposterior diameter of the spinal canal. From these measured data, patients were categorized into three groups according to spinal canal stenosis shape on CT images, as described in the modified Mayer’s classification: round, oval and trefoil [8]. Round and oval shaped spinal canal stenosis were defined according to the relation of the interpedicular distance and anteroposterior diameter of the spinal canal, and trefoil shape spinal canal stenosis by the presence of subarticular stenosis narrower than 4 mm (Fig. 1). These groups were compared with respect to clinical outcomes. Outcome assessment Clinical outcomes were graded using the visual analog scale (VAS; score range 0–10, with 0 reflecting no pain) for leg pain; functional outcomes were measured using modified Oswestry disability index (ODI; the question about sex life was not included) scores. Satisfaction rates were assessed by a single question during follow-up concerning ‘‘How would you rate the overall successfulness of the operation you received?’’ Responses thereto were graded on a scale of 1–5, with a score of 1 representing ‘‘worse than before’’; 2 presenting ‘‘failure, no relief’’; 3 presenting ‘‘not very successful, only a little relief’’; 4 presenting ‘‘fairly successful, a good deal of relief’’; and 5 representing ‘‘very successful, almost complete relief.’’ Satisfaction with the operation was defined as a score of 4 or more, and satisfaction rates for each group were calculated by dividing the number of satisfied cases by the total number cases in each group. Surgical procedures All MBDU procedures were performed as described by Young et al. and Weiner et al. [5, 7]. Briefly, the surgical procedures of MBDU were conducted after a midline skin incision and unilateral paraspinal muscle stripping as follows: Under a microscope, the superior part of the inferior
Eur Spine J
Fig. 1 Classification of spinal canal stenosis shape. a Round shape spinal canal stenosis is defined as an anteroposterior diameter of spinal canal wider than the interpedicular distance, and oval shape spinal canal stenosis is defined as the inverse thereof. Trefoil shape
spinal canal stenosis is defined as a spinal canal with subarticular stenosis narrower than 4 mm (b). This classification is based on computed tomography image a interpedicular distance; b anteroposterior diameter of spinal canal
lamina was drilled out with a high-speed drill until the lower margin of the internal layer of the ligamentum flavum was identified. The lateral portion of the lamina was then removed to the medial margin of an ipsilateral pedicle using Kerrison punches and a high-speed burr. The inferior part of the superior lamina was then drilled out, caudal to cephalad and medial to lateral, until the upper margin of the ligamentum flavum was identified superiorly. The ligamentum flavum was then easily removed. The operation table was then tilted medially, and the Caspar retractor and microscope inclined laterally. Decompression of the contralateral side was performed through the space between the inner surface of the contralateral lamina and the outer surface of the contralateral ligamentum flavum. The contralateral ligamentum flavum was removed using Kerrison punches piece by piece. Contralateral medial facetectomy was then carried out using a high-speed burr and Kerrison punches until the contralateral pedicle was identified. The contralateral neural elements were protected using cottonoid pads. In some cases, when the surgical field was inadequately exposed, the undersurface of the spinous process and lamina were partially removed (Fig. 2). The surgical view was obtained differently depending on the shape of spinal canal stenosis (Fig. 3). We could easily approach the contralateral pedicle in a wide lamina–pedicle angle in round shape spinal canal stenosis. As the angle became sharper in oval shaped spinal canal stenosis, the
Fig. 2 Illustration of ipsilateral and contralateral decompression. The lamina to the medial margin of an ipsilateral pedicle was removed, and then the medial margin of the contralateral pedicle was decompressed after protection of neural structures using cotton pads
surgical view became narrower and deeper. For trefoil shape lamina, direct vision of the contralateral area was difficult to obtain. Statistical analysis We used Statistical Package for the Social Sciences software (SPSS 12.0 K) for univariate and multivariate analyses. Data were analyzed using the paired t test and oneway ANOVA. Statistical significance was accepted for p values of \0.05.
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Fig. 3 The relations between surgical view and lamina shape. a We could easily approach the contralateral pedicle in a wide lamina– pedicle angle in round shape spinal canal stenosis. b As the angle
became sharper in oval shaped spinal canal stenosis, the surgical view became narrower and deeper. c For trefoil shape lamina, direct vision of the contralateral area was difficult to obtain
Results
shaped spinal canal stenosis were statistically less improved than those of the round and oval groups (p \ 0.01; Fig. 4). The overall satisfaction rate was 66.7 %, which included responses of ‘‘very successful’’ and ‘‘fairly successful’’ (Table 3). No significant difference was observed in satisfaction between the round and the oval shaped groups (p = 0.97), but members of the trefoil shaped group reported significantly poorer satisfaction than members of the round and oval shaped groups (p \ 0.01, Fig. 4). The postoperative complications happened in seven cases (two cases with postoperative infection, two cases with cerebrospinal fluid leakage and three cases with postoperative hematoma) and operative managements were performed in four cases. But, there were no statistical differences of postoperative complication rate according to spinal canal morphology.
In total, 144 patients with a mean age of 64 years (47–79) at surgery and a mean follow-up period of 34.6 months (24–47 months) were enrolled in this study. The preoperative durations of symptoms were \1 year in 97 patients (66.7 %), 1–3 years in 12 patients (8.3 %), and more than 3 years in 36 patients (25 %). The mean overall operation time was 104.4 min from skin incision to skin closure and the mean hospital stay was 6 days. Mean operation times for different vertebral levels were checked, and operations at level L5/S1 were twice as long as operations at levels L2/3, L3/4 and L4/5 (p \ 0.01); however, no significant difference in operation time was observed between levels L2/3, L3/4 and L4/5 (p = 0.87). As defined by the relation of the interpedicular distance and anteroposterior diameter of the spinal canal on preoperative CT images, round shaped spinal canal stenosis was observed in 42 patients, oval shaped spinal canal stenosis in 36 patients, and trefoil shape spinal canal stenosis in 66 patients (Table 1). Mean operation times and hospital stay were not significantly different among the three groups. Summarizing spinal canal stenosis shapes according to different spinal levels, notably, no cases of trefoil shaped spinal canal stenosis at levels L2/3 and L3/4 were observed. The results of clinical assessments are summarized in Tables 2 and 3. In total, mean preoperative and postoperative VAS for leg pain (at 2–3 years postoperatively) were 7.3 and 2.8, and mean preoperative and postoperative (at final follow-up) ODI were 53.8 and 24.7 % (p \ 0.01). According to spinal canal stenosis shape, mean preoperative VAS and ODI decreased with surgery, respectively, from 8.1 and 59.8 % to 2.1 and 19.1 % in the round shaped spinal canal group, from 7.2 and 47.1 % to 2.2 and 15.1 % in the oval shaped spinal canal group, and from 6.8 and 53.6 % to 3.6 and 33.3 % in the trefoil shaped spinal canal group. In all spinal canal shape groups, VAS and ODI scores significantly improved postoperatively (p \ 0.01); however, VAS and ODI scores in the cases of trefoil
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Discussion Lumbar stenosis is defined as a narrowing of the lumbar spinal canal, and is one of the most common diseases of the spine in the geriatric population [9, 10]. Although the pathophysiology of lumbar stenosis is complex, it is generally believed to be caused by a compression of neural elements, because degenerative changes include ligamentum flavum and facet joint hypertrophy and bulging of the affected intervertebral disc. As a result, the surgical treatment of lumbar stenosis typically involves wide decompression of posterior spinal elements [11]; the success rate of decompression for lumbar stenosis ranges from 57 to 95 % [12]. This classic type of decompression destroys the entire posterior arch and causes significant damage to posterior supporting tissues. Furthermore, it has been reported to cause a variety of postoperative problems, such as residual lower back pain, instability, postsurgical dead space and a prolonged recovery period [13–15]. According to several studies, preservation of posterior spinal elements
Eur Spine J Table 2 Mean preoperative and postoperative visual analog scale (VAS) for leg pain and Oswestry disability index (ODI) scores according to spinal canal stenosis shape Stenosis type
Assessment
Round (n = 42)
Preoperative
Trefoil (n = 66)
8.1 ± 1.5
2.1 ± 2.0
25.9
\0.01
19.1 ± 19.1
31.9
\0.01
VAS ODI (%)
7.2 ± 2.1 47.1 ± 18.4
2.2 ± 1.5 15.1 ± 12.2
30.6 32.1
\0.01 \0.01
6.8 ± 2.5
3.6 ± 2.7
52.9
\0.01
53.6 ± 12.7
33.3 ± 17.6
62.1
\0.01
VAS
7.3 ± 2.2
2.8 ± 2.4
38.4
\0.01
53.8 ± 16.0
24.7 ± 18.7
45.9
\0.01
VAS ODI (%)
Table 3 Postoperative satisfaction rates according to spinal canal stenosis shape Stenosis type
Satisfaction measurea 1
2
Round
0
0
Oval
0
0
3
b
p value
59.8 ± 7.3
ODI (%) Total (n = 144)
Change (postoperative/ preoperative) (%)
ODI (%)
VAS
Oval (n = 36)
Postoperative
Total
Satisfaction rate (%)
4
5
6
18
18
42
85.7
6
12
18
36
83.3
Trefoil
0
6
30
18
12
66
45.4c
Total
0
6
42
48
45
144
66.7
a
Satisfaction scored from 1 to 5 represents, respectively, ‘‘worse than before,’’ ‘‘failure, no relief,’’ ‘‘not very successful, only a little relief,’’ ‘‘fairly successful, a good deal of relief,’’ and ‘‘very successful, almost complete relief’’
b
Noticeably, all 6 persons who reported ‘‘failure, no relief’’ exhibited trefoil shaped spinal canal stenosis
c
Trefoil shaped spinal canal stenosis showed poor outcomes in regard to satisfaction rate (p \ 0.01)
has a beneficial effect on the maintenance of spinal stability [11, 13, 14, 16]. Instead of combining fusion with decompression and thus maximizing surgery and associated perioperative risks, other investigators have attempted to lower the operative failure rate by minimizing the invasiveness of the decompressive procedure [15]. Fenestration with minimal soft tissue dissection and limited bone removal, instead of an extensive laminectomy, to prevent subsequent lumbar instability has become widely accepted for the treatment of spinal stenosis [7, 17–20]. In addition, a unilateral approach for bilateral decompression has been modified and successfully performed by many surgeons [3, 19, 21, 22]. Accordingly, decompression is advocated whenever history, symptoms, findings, and imaging clearly indicate its use in patients with lumbar spinal stenosis refractory to conservative treatment for at least 3 months [23]. Notwithstanding, there is still a lack of evidence-based data regarding the different surgical techniques for lumbar spinal decompression [20, 23–25]. It is difficult to compare the different procedures in terms of their success rate,
because the outcome parameters reported in many studies vary. Indeed, further issues, such as comorbidities of the patients, may influence outcomes after surgical decompression of lumbar spinal stenosis [26]. Furthermore, spinerelated adverse events such as osteoporosis, postsurgical instability, and extensive multilevel surgery are wellknown to complicate medium- and long-term outcomes [23, 27–29]. Despite these limitations, a few recent studies reported good clinical results for MBDU not only in lumbar spinal canal stenosis [9, 15, 20, 23, 31–33], but also in grade I lumbar degenerative spondylolisthesis [15, 30, 32– 34]. However, a report comparing less invasive decompression techniques, such as bilateral and unilateral laminotomy, as well as laminectomy, showed that MBDU had less of a benefit than bilateral laminotomy as an alternative treatment for lumbar spinal stenosis [20]. Reportedly, patient satisfaction rate was significantly superior in the bilateral laminotomy group than in the MBDU and laminectomy groups (p \ 0.01). In this regard, the authors further commented that the asymmetrical approach led to greater residual pain, particularly in the low back, compared with the bilateral laminotomy, although the reason therefore was unclear [20]. Furthermore, other authors in similar clinical studies also commented that older age and chronic comorbidities relating to a systemic problem could affect clinical results [10]. However, in the present clinical study, we considered that the different spinal canal morphologies could affect the clinical outcomes. Spinal canal stenosis can involve the central spinal canal, its lateral recess, the intervertebral foramina, or all three components. Spinal canal stenosis may be developmental or, as is more common, an acquired disease from numerous causes [35]. In this study, patients were categorized into three groups according to spinal canal stenosis shape on CT images as described in the modified Mayer’s classification, including round, oval, and trefoil [8]. Round (42 patients) and oval shaped (36 patients) spinal canal stenoses were defined according to the relation of the interpedicular distance and the anteroposterior diameter of
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Eur Spine J Fig. 4 Comparison of clinical assessments among the different spinal canal stenosis shapes. Statistically significant differences with a p value of \0.01 are indicated by asterisks
the spinal canal, and trefoil shaped (66 patients) spinal canal stenosis by the presence of subarticular stenosis narrower than 4 mm (Fig. 1). In all groups, clinical parameters (VAS, ODI, and satisfaction rate) significantly improved postoperatively (p \ 0.01); however, the degree
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of improvement in the clinical parameters differed according to the shape of spinal canal stenosis. The trefoil shaped spinal canal stenosis group demonstrated significantly poorer clinical outcomes than the round and/or oval shaped spinal canal stenosis groups (p \ 0.01, Fig. 4).
Eur Spine J
Differences in the surgical view according to the shape of spinal canal stenosis were the main reason for the varying improvements in clinical parameters among the spinal canal stenosis groups (Figs. 3, 4). The contralateral pedicle approach with a wide lamina–pedicle angle was easily accessible in round shaped spinal canal stenosis. Although the surgical view became narrower and deeper as the lamina–pedicle angle became sharper, a contralateral pedicle approach could be taken to access oval shaped spinal canal stenosis. However, a direct vision of the contralateral area was difficult to obtain in the trefoil shaped lamina. As a result, adequate decompression of the spinal canal stenosis was difficult to attain due to limited exposure of the contralateral area, and resulted in the lack of greater clinical improvement in trefoil shaped spinal canal stenosis. There are some limitations in this study. First, the indications for this surgical procedure were limited to patients with single-level spinal lumbar stenosis. Second, this study focused only on the inner laminar morphology of the spinal canal. Although there are various types of stenosis, cases of high-level lumbar and round shaped laminar stenosis due to calcified disc herniation with mild ligamentum flavum hypertrophy and facet thickening were not included in this analysis; these ventral compressive cases would have required less neural tissue manipulation during decompression, unrelated to the laminar shape. Despite these limitations, this report is the first to analyze and document the clinical outcomes of MBDU according to spinal canal morphology in degenerative lumbar spinal stenosis.
Conclusion Microsurgical bilateral decompression via a unilateral approach for lumbar spinal stenosis is a less invasive operative technique and may be a good modality for treating round or oval shaped spinal canal stenosis. However, this technique was shown to be less effective in trefoil shaped spinal canal stenosis, and therefore greater consideration must be taken before applying this technique in the treatment of trefoil shaped spinal canal stenosis. The current authors recommend performing the bilateral decompression technique in cases of trefoil shaped spinal canal stenosis.
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18. Conflict of interest There were no conflicts of interest in concerning this article. We received no financial support into produce this article.
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ORIGINAL ARTICLE
Spinal canal morphology and clinical outcomes of microsurgical bilateral decompression via a unilateral approach for lumbar spinal canal stenosis Won-Seok Choi • Chang Hyun Oh • Gyu Yeul Ji • Sung Chan Shin • Jang-Bo Lee Dong-Hyuk Park • Tai-Hyoung Cho
•
Received: 7 August 2013 / Revised: 12 November 2013 / Accepted: 14 November 2013 Ó Springer-Verlag Berlin Heidelberg 2013
Abstract Purpose Microsurgical bilateral decompression via a unilateral approach for lumbar spinal stenosis is a less invasive technique compared to conventional laminectomy. Although many technical reports have demonstrated acceptable overall surgical outcomes for this approach, no studies have attempted to clarify the clinical outcomes thereof in regard to anatomical variance of the spinal canal. This study was conducted to analyze the clinical outcomes of microsurgical bilateral decompression via a unilateral approach according to spinal canal morphology in degenerative lumbar spinal stenosis. Methods Between January 2008 and December 2009, 144 patients with single-level spinal lumbar stenosis underwent microsurgical bilateral decompression via a unilateral approach by a single surgeon. Patients were categorized into three groups according to spinal canal shape: round
W.-S. Choi and C. H. Oh contributed equally to this project and should be considered co-first authors. W.-S. Choi C. H. Oh Department of Neurosurgery, Spine and Joint Research Institute, Guro Teun Teun Hospital, Seoul, Republic of Korea G. Y. Ji Department of Neurosurgery, Yonsei University College of Medicine, Seoul, Republic of Korea S. C. Shin Department of Neurosurgery, Jangan-dong Teun Teun Hospital, Seoul, Republic of Korea J.-B. Lee D.-H. Park T.-H. Cho (&) Department of Neurosurgery, Korea University Anam Hospital, Korea University College of Medicine, 126-1, 5-ga, Anam-dong, Seongbuk-gu, Seoul 136-705, Republic of Korea e-mail: [email protected]
(n = 42), oval (n = 36), and trefoil (n = 66), and clinical parameters were assessed both before and after surgery with 2–3 years of follow-up. Results Mean visual analog scale (VAS) and Oswestry disability index (ODI) decreased after surgery, respectively, from 8.1 and 59.8 % to 2.1 and 19.1 % in the round shaped spinal canal group, from 7.2 and 47.1 % to 2.2 and 15.1 % in the oval shaped spinal canal group, and from 6.8 and 53.6 % to 3.6 and 33.3 % in the trefoil shaped spinal canal group. In all groups, VAS and ODI scores significantly improved postoperatively (p \ 0.01), although less improved VAS and ODI scores were observed in the trefoil shaped spinal canal group (p \ 0.01). The overall patient satisfaction rate was 66.7 %; however, statistically significant lower satisfaction rates were reported in the trefoil shaped spinal canal group (p \ 0.01). Conclusions Microsurgical bilateral decompression via a unilateral approach may be a good modality for treating round or oval shape spinal canal stenosis, but is not recommended for trefoil-shaped-stenosis. The current authors recommend performing the bilateral decompression technique in cases of trefoil-shaped-spinal canal stenosis. Keywords Microsurgical bilateral decompression Unilateral approach Spinal canal stenosis Clinical result
Introduction Lumbar spinal stenosis is a common disease treated by spinal surgery. The traditional treatment of spinal stenosis involves performing a wide laminectomy with sufficient decompression and undercutting of the medial facet with a foraminotomy [1–3]. To alleviate spinal instability
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Eur Spine J Table 1 Spinal canal stenosis shapes according to spinal level Level
Spinal canal stenosis shape Round
Oval
Trefoil
Total
L2/3
0
6
0a
6
L3/4
6
12
0a
18
L4/5
24
18
42
84
L5/S1
12
0
24
36
Total
42
36
66
144
a
There were no cases of trefoil shaped spinal canal stenosis at levels L2/3 and L3/4
following a conventional laminectomy, which may cause deterioration of symptoms, less invasive decompressive procedures such as microsurgical bilateral decompression via a unilateral approach (MBDU) have been introduced for the treatment of spinal stenosis [4–8]. As bilateral decompression via a unilateral approach requires the performance of an unroofing technique, anatomical variance of the spinal canal could be an important factor for applying MBDU for lumbar spinal stenosis. However, to our knowledge, none have reported on the clinical outcomes of MBDU in regard to anatomical variance of the spinal canal. We, therefore, attempted to assess the clinical outcomes of MBDU according to the shape of spinal canal stenosis with a minimum of 2 years follow-up.
Materials and methods Patient population This retrospective analysis study was conducted at a single institution between January 2008 and December 2009 after gaining approval from the Teun Teun institutional review board. One hundred forty-four subjects with single-level spinal lumbar stenosis underwent MBDU by a single surgeon on an established evaluation and follow-up protocol. The mean age of the patients was 64 years (range from 47 to 79 years), and 78 patients were male. We retrospectively reviewed office charts, hospital charts, and radiologic studies to assess preoperative symptomatology, findings on clinical examinations, and radiologic characteristics. All cases were administered conservative care for at least 2 months, and cases who demonstrated limited benefit from conservative treatment were selected as candidates for this technique. The inclusion criteria for patients were a presence of single-level spinal lumbar stenosis, chronic and persistent radiculopathy despite conservative treatment, progressive neurologic deficits, persistent and unremitting lower back pain for more than 3 months, loss of quality of life because
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of neurological claudication, and a minimum follow-up period of 2 years. The exclusion criteria for the patients were previous spine surgery, a compression fracture or instability at the segments including degenerative spondylolisthesis, and patients who underwent simultaneous decompression at adjacent segments. Type of spinal canal stenosis We performed radiologic assessments preoperatively. Radiographic assessments were made by two different independent observers including the treating surgeon. Preoperative computed tomography (CT) images were evaluated to assess the interpedicular distance and the anteroposterior diameter of the spinal canal. From these measured data, patients were categorized into three groups according to spinal canal stenosis shape on CT images, as described in the modified Mayer’s classification: round, oval and trefoil [8]. Round and oval shaped spinal canal stenosis were defined according to the relation of the interpedicular distance and anteroposterior diameter of the spinal canal, and trefoil shape spinal canal stenosis by the presence of subarticular stenosis narrower than 4 mm (Fig. 1). These groups were compared with respect to clinical outcomes. Outcome assessment Clinical outcomes were graded using the visual analog scale (VAS; score range 0–10, with 0 reflecting no pain) for leg pain; functional outcomes were measured using modified Oswestry disability index (ODI; the question about sex life was not included) scores. Satisfaction rates were assessed by a single question during follow-up concerning ‘‘How would you rate the overall successfulness of the operation you received?’’ Responses thereto were graded on a scale of 1–5, with a score of 1 representing ‘‘worse than before’’; 2 presenting ‘‘failure, no relief’’; 3 presenting ‘‘not very successful, only a little relief’’; 4 presenting ‘‘fairly successful, a good deal of relief’’; and 5 representing ‘‘very successful, almost complete relief.’’ Satisfaction with the operation was defined as a score of 4 or more, and satisfaction rates for each group were calculated by dividing the number of satisfied cases by the total number cases in each group. Surgical procedures All MBDU procedures were performed as described by Young et al. and Weiner et al. [5, 7]. Briefly, the surgical procedures of MBDU were conducted after a midline skin incision and unilateral paraspinal muscle stripping as follows: Under a microscope, the superior part of the inferior
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Fig. 1 Classification of spinal canal stenosis shape. a Round shape spinal canal stenosis is defined as an anteroposterior diameter of spinal canal wider than the interpedicular distance, and oval shape spinal canal stenosis is defined as the inverse thereof. Trefoil shape
spinal canal stenosis is defined as a spinal canal with subarticular stenosis narrower than 4 mm (b). This classification is based on computed tomography image a interpedicular distance; b anteroposterior diameter of spinal canal
lamina was drilled out with a high-speed drill until the lower margin of the internal layer of the ligamentum flavum was identified. The lateral portion of the lamina was then removed to the medial margin of an ipsilateral pedicle using Kerrison punches and a high-speed burr. The inferior part of the superior lamina was then drilled out, caudal to cephalad and medial to lateral, until the upper margin of the ligamentum flavum was identified superiorly. The ligamentum flavum was then easily removed. The operation table was then tilted medially, and the Caspar retractor and microscope inclined laterally. Decompression of the contralateral side was performed through the space between the inner surface of the contralateral lamina and the outer surface of the contralateral ligamentum flavum. The contralateral ligamentum flavum was removed using Kerrison punches piece by piece. Contralateral medial facetectomy was then carried out using a high-speed burr and Kerrison punches until the contralateral pedicle was identified. The contralateral neural elements were protected using cottonoid pads. In some cases, when the surgical field was inadequately exposed, the undersurface of the spinous process and lamina were partially removed (Fig. 2). The surgical view was obtained differently depending on the shape of spinal canal stenosis (Fig. 3). We could easily approach the contralateral pedicle in a wide lamina–pedicle angle in round shape spinal canal stenosis. As the angle became sharper in oval shaped spinal canal stenosis, the
Fig. 2 Illustration of ipsilateral and contralateral decompression. The lamina to the medial margin of an ipsilateral pedicle was removed, and then the medial margin of the contralateral pedicle was decompressed after protection of neural structures using cotton pads
surgical view became narrower and deeper. For trefoil shape lamina, direct vision of the contralateral area was difficult to obtain. Statistical analysis We used Statistical Package for the Social Sciences software (SPSS 12.0 K) for univariate and multivariate analyses. Data were analyzed using the paired t test and oneway ANOVA. Statistical significance was accepted for p values of \0.05.
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Fig. 3 The relations between surgical view and lamina shape. a We could easily approach the contralateral pedicle in a wide lamina– pedicle angle in round shape spinal canal stenosis. b As the angle
became sharper in oval shaped spinal canal stenosis, the surgical view became narrower and deeper. c For trefoil shape lamina, direct vision of the contralateral area was difficult to obtain
Results
shaped spinal canal stenosis were statistically less improved than those of the round and oval groups (p \ 0.01; Fig. 4). The overall satisfaction rate was 66.7 %, which included responses of ‘‘very successful’’ and ‘‘fairly successful’’ (Table 3). No significant difference was observed in satisfaction between the round and the oval shaped groups (p = 0.97), but members of the trefoil shaped group reported significantly poorer satisfaction than members of the round and oval shaped groups (p \ 0.01, Fig. 4). The postoperative complications happened in seven cases (two cases with postoperative infection, two cases with cerebrospinal fluid leakage and three cases with postoperative hematoma) and operative managements were performed in four cases. But, there were no statistical differences of postoperative complication rate according to spinal canal morphology.
In total, 144 patients with a mean age of 64 years (47–79) at surgery and a mean follow-up period of 34.6 months (24–47 months) were enrolled in this study. The preoperative durations of symptoms were \1 year in 97 patients (66.7 %), 1–3 years in 12 patients (8.3 %), and more than 3 years in 36 patients (25 %). The mean overall operation time was 104.4 min from skin incision to skin closure and the mean hospital stay was 6 days. Mean operation times for different vertebral levels were checked, and operations at level L5/S1 were twice as long as operations at levels L2/3, L3/4 and L4/5 (p \ 0.01); however, no significant difference in operation time was observed between levels L2/3, L3/4 and L4/5 (p = 0.87). As defined by the relation of the interpedicular distance and anteroposterior diameter of the spinal canal on preoperative CT images, round shaped spinal canal stenosis was observed in 42 patients, oval shaped spinal canal stenosis in 36 patients, and trefoil shape spinal canal stenosis in 66 patients (Table 1). Mean operation times and hospital stay were not significantly different among the three groups. Summarizing spinal canal stenosis shapes according to different spinal levels, notably, no cases of trefoil shaped spinal canal stenosis at levels L2/3 and L3/4 were observed. The results of clinical assessments are summarized in Tables 2 and 3. In total, mean preoperative and postoperative VAS for leg pain (at 2–3 years postoperatively) were 7.3 and 2.8, and mean preoperative and postoperative (at final follow-up) ODI were 53.8 and 24.7 % (p \ 0.01). According to spinal canal stenosis shape, mean preoperative VAS and ODI decreased with surgery, respectively, from 8.1 and 59.8 % to 2.1 and 19.1 % in the round shaped spinal canal group, from 7.2 and 47.1 % to 2.2 and 15.1 % in the oval shaped spinal canal group, and from 6.8 and 53.6 % to 3.6 and 33.3 % in the trefoil shaped spinal canal group. In all spinal canal shape groups, VAS and ODI scores significantly improved postoperatively (p \ 0.01); however, VAS and ODI scores in the cases of trefoil
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Discussion Lumbar stenosis is defined as a narrowing of the lumbar spinal canal, and is one of the most common diseases of the spine in the geriatric population [9, 10]. Although the pathophysiology of lumbar stenosis is complex, it is generally believed to be caused by a compression of neural elements, because degenerative changes include ligamentum flavum and facet joint hypertrophy and bulging of the affected intervertebral disc. As a result, the surgical treatment of lumbar stenosis typically involves wide decompression of posterior spinal elements [11]; the success rate of decompression for lumbar stenosis ranges from 57 to 95 % [12]. This classic type of decompression destroys the entire posterior arch and causes significant damage to posterior supporting tissues. Furthermore, it has been reported to cause a variety of postoperative problems, such as residual lower back pain, instability, postsurgical dead space and a prolonged recovery period [13–15]. According to several studies, preservation of posterior spinal elements
Eur Spine J Table 2 Mean preoperative and postoperative visual analog scale (VAS) for leg pain and Oswestry disability index (ODI) scores according to spinal canal stenosis shape Stenosis type
Assessment
Round (n = 42)
Preoperative
Trefoil (n = 66)
8.1 ± 1.5
2.1 ± 2.0
25.9
\0.01
19.1 ± 19.1
31.9
\0.01
VAS ODI (%)
7.2 ± 2.1 47.1 ± 18.4
2.2 ± 1.5 15.1 ± 12.2
30.6 32.1
\0.01 \0.01
6.8 ± 2.5
3.6 ± 2.7
52.9
\0.01
53.6 ± 12.7
33.3 ± 17.6
62.1
\0.01
VAS
7.3 ± 2.2
2.8 ± 2.4
38.4
\0.01
53.8 ± 16.0
24.7 ± 18.7
45.9
\0.01
VAS ODI (%)
Table 3 Postoperative satisfaction rates according to spinal canal stenosis shape Stenosis type
Satisfaction measurea 1
2
Round
0
0
Oval
0
0
3
b
p value
59.8 ± 7.3
ODI (%) Total (n = 144)
Change (postoperative/ preoperative) (%)
ODI (%)
VAS
Oval (n = 36)
Postoperative
Total
Satisfaction rate (%)
4
5
6
18
18
42
85.7
6
12
18
36
83.3
Trefoil
0
6
30
18
12
66
45.4c
Total
0
6
42
48
45
144
66.7
a
Satisfaction scored from 1 to 5 represents, respectively, ‘‘worse than before,’’ ‘‘failure, no relief,’’ ‘‘not very successful, only a little relief,’’ ‘‘fairly successful, a good deal of relief,’’ and ‘‘very successful, almost complete relief’’
b
Noticeably, all 6 persons who reported ‘‘failure, no relief’’ exhibited trefoil shaped spinal canal stenosis
c
Trefoil shaped spinal canal stenosis showed poor outcomes in regard to satisfaction rate (p \ 0.01)
has a beneficial effect on the maintenance of spinal stability [11, 13, 14, 16]. Instead of combining fusion with decompression and thus maximizing surgery and associated perioperative risks, other investigators have attempted to lower the operative failure rate by minimizing the invasiveness of the decompressive procedure [15]. Fenestration with minimal soft tissue dissection and limited bone removal, instead of an extensive laminectomy, to prevent subsequent lumbar instability has become widely accepted for the treatment of spinal stenosis [7, 17–20]. In addition, a unilateral approach for bilateral decompression has been modified and successfully performed by many surgeons [3, 19, 21, 22]. Accordingly, decompression is advocated whenever history, symptoms, findings, and imaging clearly indicate its use in patients with lumbar spinal stenosis refractory to conservative treatment for at least 3 months [23]. Notwithstanding, there is still a lack of evidence-based data regarding the different surgical techniques for lumbar spinal decompression [20, 23–25]. It is difficult to compare the different procedures in terms of their success rate,
because the outcome parameters reported in many studies vary. Indeed, further issues, such as comorbidities of the patients, may influence outcomes after surgical decompression of lumbar spinal stenosis [26]. Furthermore, spinerelated adverse events such as osteoporosis, postsurgical instability, and extensive multilevel surgery are wellknown to complicate medium- and long-term outcomes [23, 27–29]. Despite these limitations, a few recent studies reported good clinical results for MBDU not only in lumbar spinal canal stenosis [9, 15, 20, 23, 31–33], but also in grade I lumbar degenerative spondylolisthesis [15, 30, 32– 34]. However, a report comparing less invasive decompression techniques, such as bilateral and unilateral laminotomy, as well as laminectomy, showed that MBDU had less of a benefit than bilateral laminotomy as an alternative treatment for lumbar spinal stenosis [20]. Reportedly, patient satisfaction rate was significantly superior in the bilateral laminotomy group than in the MBDU and laminectomy groups (p \ 0.01). In this regard, the authors further commented that the asymmetrical approach led to greater residual pain, particularly in the low back, compared with the bilateral laminotomy, although the reason therefore was unclear [20]. Furthermore, other authors in similar clinical studies also commented that older age and chronic comorbidities relating to a systemic problem could affect clinical results [10]. However, in the present clinical study, we considered that the different spinal canal morphologies could affect the clinical outcomes. Spinal canal stenosis can involve the central spinal canal, its lateral recess, the intervertebral foramina, or all three components. Spinal canal stenosis may be developmental or, as is more common, an acquired disease from numerous causes [35]. In this study, patients were categorized into three groups according to spinal canal stenosis shape on CT images as described in the modified Mayer’s classification, including round, oval, and trefoil [8]. Round (42 patients) and oval shaped (36 patients) spinal canal stenoses were defined according to the relation of the interpedicular distance and the anteroposterior diameter of
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Eur Spine J Fig. 4 Comparison of clinical assessments among the different spinal canal stenosis shapes. Statistically significant differences with a p value of \0.01 are indicated by asterisks
the spinal canal, and trefoil shaped (66 patients) spinal canal stenosis by the presence of subarticular stenosis narrower than 4 mm (Fig. 1). In all groups, clinical parameters (VAS, ODI, and satisfaction rate) significantly improved postoperatively (p \ 0.01); however, the degree
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of improvement in the clinical parameters differed according to the shape of spinal canal stenosis. The trefoil shaped spinal canal stenosis group demonstrated significantly poorer clinical outcomes than the round and/or oval shaped spinal canal stenosis groups (p \ 0.01, Fig. 4).
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Differences in the surgical view according to the shape of spinal canal stenosis were the main reason for the varying improvements in clinical parameters among the spinal canal stenosis groups (Figs. 3, 4). The contralateral pedicle approach with a wide lamina–pedicle angle was easily accessible in round shaped spinal canal stenosis. Although the surgical view became narrower and deeper as the lamina–pedicle angle became sharper, a contralateral pedicle approach could be taken to access oval shaped spinal canal stenosis. However, a direct vision of the contralateral area was difficult to obtain in the trefoil shaped lamina. As a result, adequate decompression of the spinal canal stenosis was difficult to attain due to limited exposure of the contralateral area, and resulted in the lack of greater clinical improvement in trefoil shaped spinal canal stenosis. There are some limitations in this study. First, the indications for this surgical procedure were limited to patients with single-level spinal lumbar stenosis. Second, this study focused only on the inner laminar morphology of the spinal canal. Although there are various types of stenosis, cases of high-level lumbar and round shaped laminar stenosis due to calcified disc herniation with mild ligamentum flavum hypertrophy and facet thickening were not included in this analysis; these ventral compressive cases would have required less neural tissue manipulation during decompression, unrelated to the laminar shape. Despite these limitations, this report is the first to analyze and document the clinical outcomes of MBDU according to spinal canal morphology in degenerative lumbar spinal stenosis.
Conclusion Microsurgical bilateral decompression via a unilateral approach for lumbar spinal stenosis is a less invasive operative technique and may be a good modality for treating round or oval shaped spinal canal stenosis. However, this technique was shown to be less effective in trefoil shaped spinal canal stenosis, and therefore greater consideration must be taken before applying this technique in the treatment of trefoil shaped spinal canal stenosis. The current authors recommend performing the bilateral decompression technique in cases of trefoil shaped spinal canal stenosis.
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18. Conflict of interest There were no conflicts of interest in concerning this article. We received no financial support into produce this article.
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