The Spine Journal 13 (2013) 914–921
Clinical Study
Is cervical lordosis relevant in laminoplasty? Seok Woo Kim, MD, PhDa, Dinh Manh Hai, MDa, Shanmuga Sundaram, MSa, Yong Chan Kim, MDa, Moon Soo Park, MDa, Sang-Hoon Paik, MDa, Yoon-Hae Kwak, MDb, Tae-Hwan Kim, MDa,* a
Spine Center, Hallym University Sacred Heart Hospital, College of Medicine, Hallym University, 896, Pyeongchon-dong, Dongan-gu, Anyang-si, Gyeonggi-do 431-070, South Korea b Orthopedic Department, Hallym University Sacred Heart Hospital, College of Medicine, Hallym University, 896, Pyeongchon-dong, Dongan-gu, Anyang-si, Gyeonggi-do 431-070, South Korea Received 21 March 2012; revised 7 November 2012; accepted 18 February 2013
Abstract
BACKGROUND CONTEXT: Laminoplasty aims to decompress the spinal cord and stabilize the cervical spine in patients with multilevel cervical lesions. Not every patient with cervical compressive myelopathy is a good candidate for laminoplasty. Most studies recommend that neutral or kyphotic alignments are contraindications for laminoplasty. However, cervical sagittal alignment does not have a strong and consistent effect on the clinical outcomes of laminoplasty. Moreover, many reports on the effect of cervical sagittal alignment did not designate the ideal definition of alignment and used different definitions of lordosis. PURPOSE: To identify the effect of preoperative cervical alignment according to two different definitions after midline splitting double-door laminoplasty. STUDY DESIGN: Retrospective cohort study. PATIENT SAMPLE: From August 2008 to September 2010, 58 patients were diagnosed with cervical myelopathy and treated with midline splitting double-door laminoplasty. OUTCOME MEASURES: The clinical results were assessed with the modified Japanese Orthopedic Association (JOA) score, neck disability index (NDI), and visual analog scale (VAS) and were compared to analyze the rate of change between preoperative and postoperative values. Postoperative radiological results at the final follow-up examinations were compared between groups to obtain the change in range of motion and sagittal alignment. METHOD: The effect of cervical alignment on JOA, NDI, and VAS scales and also on change of alignment and change of range of motion (ROM) at the final follow-up examinations was analyzed statistically between two groups according to two different definitions such as Toyama classification and Cobb angle. RESULTS: No difference was found between the two groups according to Toyama classification in terms of the postoperative improvement rate of the modified JOA score (p5.086), decreasing rate of the VAS (p5.940) or NDI (p5.211), postoperatively. Additionally, no difference was found for the decreasing rate of ROM (p5.427) or sagittal alignment (p5.864) based on the radiological evaluation results. Also, there was no difference between two groups according to Cobb angle in terms of the modified JOA score (p5.743), VAS (p5.548), or NDI (p5.32), postoperatively. Additionally, no difference was found for the ROM (p51.000) or sagittal alignment (p5.440) based on the radiological evaluation results. CONCLUSIONS: Despite nonlordosis cervical sagittal alignment, double-door laminoplasty would be effective for patients with cervical myelopathy because of cervical spondylotic myelopathy or ossification of the posterior longitudinal ligament. Furthermore, sagittal alignment is not the
FDA device/drug status: Not applicable. Author disclosures: SWK: Nothing to disclose. DMH: Nothing to disclose. SS: Nothing to disclose. YCK: Nothing to disclose. MSP: Nothing to disclose. S-HP: Nothing to disclose. Y-HK: Nothing to disclose. T-HK: Nothing to disclose. 1529-9430/$ - see front matter Ó 2013 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.spinee.2013.02.032
* Corresponding author. Spine Center, Hallym University Sacred Heart Hospital, College of Medicine, Hallym University, 896, Pyeongchon-dong, Dongan-gu, Anyang-si, Gyeonggi-do 431-070, South Korea. Tel.: (82) 107210-0460. E-mail address:
[email protected] (T.-H. Kim)
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absolute and sole factor that surgeons should consider when determining the optimal treatment strategy. Ó 2013 Elsevier Inc. All rights reserved. Keywords:
Midline splitting double-door laminoplasty; Cervical myelopathy; Sagittal alignment; Laminoplasty
Introduction Laminoplasty aims to decompress the spinal cord and stabilize the cervical spine in patients with multilevel cervical lesions, which are caused by cervical spondylotic myelopathy (CSM), ossification of the posterior longitudinal ligament (OPLL), and multiple intervertebral disc herniations with developmental spinal canal stenosis. This surgical technique preserves the integrity of the posterior bone-ligament structure and thus maintains stability immediately after surgery [1,2]. Several laminoplasty techniques have been developed to improve the surgical outcomes and reduce complications, including axial neck pain, C5 nerve palsy, and postoperative progression of kyphosis. In long-term studies, the clinical outcomes of the several types of laminoplasty were similar, which suggests that the neurological recovery achieved in the short term lasted over 10 years [3–6]. Not every patient with cervical compressive myelopathy is a good candidate for laminoplasty, and the optimal choice of the surgical technique for CSM or OPLL is not easily made for many reasons [7–11]. Generally, the number of involved segments, alignment of the cervical spine, type of OPLL, and instability of the subaxial cervical spine are main concerns [12–15]. Among these factors, cervical alignment was considered to play an important role in the maintenance of laminoplasty results. Most studies recommend that neutral or kyphotic alignments are contraindications for laminoplasty. Because laminoplasty is a type of indirect decompression, remaining anterior compressive structures may disturb neurological recovery [16–18]. Many studies have shown that a greater posterior shift achieved by lordotic alignment is correlated with an excellent clinical outcome [9,19–22]. Some authors emphasize that the posterior shift of the cord is an important role of laminoplasty and that the factors related to posterior drift are strongly prognostic, such as preoperative cervical sagittal alignment, the space available for the spinal cord at cephalad/caudal levels for the decompression, longitudinal distance index, and decompression scope [19,20,23–25]. However, cervical sagittal alignment does not have a strong and consistent effect on the clinical outcomes of laminoplasty [9,25,26]. Moreover, many reports on the effect of cervical sagittal alignment did not designate the ideal definition of alignment [17,18,27] and used different definitions of lordosis, such as Cobb angle with different values [9,28,29], vertical line at C2 and C7 [23], and K line [30]. In addition, most laminoplasty procedures addressed in many reports on cervical alignment were unilateral open-door laminoplasty procedures, also called the Hirabayashi technique.
According to the authors’ experience, in more than 200 cases of double-door laminoplasty, a certain number of patients with preoperative kyphotic alignment had acceptable or satisfactory outcomes. The purpose of the present study was to identify the effect of preoperative cervical alignment. We compared the clinical and radiological outcomes after double-door laminoplasty according to two different definitions of cervical alignment that were the most commonly used in the other reports.
Materials and methods From August 2008 to September 2010, 58 patients in the authors’ hospital who were diagnosed with cervical myelopathy and treated with double-door laminoplasty (a method used to decompress the spinal canal by splitting the midline of the spinous process) were analyzed retrospectively. Forty men and 18 women with an average age of 57.4 years (range 32–74 years) were enrolled in the study (Table 1). The mean clinical and radiological follow-up was 18.8 months (range 3–48 months). Exclusion criteria included kyphosis of more than 15 or more than 60 percent canal involvement of the posterior longitudinal ligament based on the radiological findings. Cervical kyphosis or lordosis was measured from the lower end plate of C2 to the lower end plate of C7 (Fig. 1). Additionally, patients with rheumatoid arthritis, tumor, trauma, infection, or congenital disorders were excluded from this study. Preoperative cervical sagittal alignment of the cervical spine was assessed on a neutral, lateral radiograph. Preoperative radiographic evaluation included static and dynamic, flexion-extension X-ray in an upright position, computed tomography, and magnetic resonance imaging (MRI). Postoperative radiographs were obtained at each follow-up visit. A posterior incision was made along the nuchal ligament to the line of the spinous processes. The semispinalis cervicis was partially detached from the lower margin of C2 spinous process. Cervical laminae were exposed laterally to the medial aspect of the facet joints, and the interspinous ligaments were removed. The involved spinous processes were split sagittally with a Tomita saw (T-saw; Medtronics, Memphis, TN, USA). The T-saw was 0.54 mm in diameter. It cuts along the midline epidural space in a caudal-tocranial direction. The advancing tip of the polyethylene sleeve was grasped as it appeared in the flavectomy at the other end of the decompression zone. The T-saw was
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Context The theory behind laminoplasty holds that by unroofing the canal posteriorly, the spinal cord can ‘‘move away’’ from any anterior pathology, affording decompression. For most surgeons considering laminoplasty, ‘‘moving away’’ requires a native cervical lordosis at the stenotic segments. Contribution In this retrospective study, the authors found that patients undergoing laminoplasty with kyphosis up to 15 degrees and anterior compression up to 60% of the canal diameter did equally as well as those patients with lordosis. Implications If further studies with long-term outcome assessments (with larger numbers and good baseline comparisons) support these findings, the indications for laminoplasty might be expanded to include milder forms of kyphosis. —The Editors
advanced through the sleeve so that it could be held securely whereas the sleeve was withdrawn retrograde over the saw. At this point, the unsheathed saw spanned the midline of the spinal canal along the area to be decompressed. Each end was grasped with a special clamp or needle holder. The T-saw was pulled tight before initiating a reciprocating motion. The T-saw should fit snugly just at the midline of the inner wall of the laminar arch. Continuous reciprocating motion cut the midline of the inner wall of the laminar arch and the spinous processes in a ventralto-dorsal direction away from the dura and spinal cord. The supra- and interspinous ligaments were automatically dissected at the midline. The saw was frequently lubricated with sterile saline solution to avoid excessive heat and Table 1 Patient demographics Variable
Data
Number Gender Male Female Age (y, mean6SD) Number of operated segments (patients) More than four segments Less than three segments Pathology (patients) CSM OPLL Follow-up (mo, mean6SD)
58 40 18 57.4622.5 35 23 28 30 18.7615.6
CSM, cervical spondylotic myelopathy; OPLL, ossification of the posterior longitudinal ligament; SD, standard deviation.
Fig. 1. Cobb angle from C2 to C7 was used as a measure of sagittal alignment. According to this angle, we divided patients into two groups.
friction [31]. After bilateral gutters for the hinges were carefully made with a high-speed burr at the transitional area between the facet joint and the laminae, spinal canal enlargement was achieved by opening the split laminae bilaterally with a spreader and placing hydroxyapatite (Apaceram-AX, Hoya Co., Tokyo, Japan) or allo-bone graft (Laminar Spacer-K; CG Bio, Seoul, Korea). The definitions of cervical lordosis used in this study were those according to Cobb angle (Fig. 1) and Toyama classification [24] (Fig. 2). The patients with a Cobb angle of less than 10 were designated as the ‘‘nonlordotic group,’’ and those with an angle of 10 or more were designated as the ‘‘lordotic group.’’ After the surgery, clinical and radiological results in these two groups were compared. After Toyama classification, the patients were divided into a lordosis group and a nonlordosis group, the latter including patients with straight, sigmoid, or kyphotic curvature. These groups were compared according to the same clinical and radiological outcomes. We analyzed disease entity, age, gender, and number of surgical segments to investigate the factors that affected the
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Fig. 2. Toyama classification: according to the relationship of vertebral bodies of C3, C4, C5, and C6 to a virtual straight line drawn from the posteroinferior border of the body of C2 to that of C7, patients were divided into four groups: the lordotic group and the straight, sigmoid, and kyphosis groups, which are included in the nonlordotic group. Lordosis was defined when posterior cortices of all the vertebral bodies from C3 to C6 were anterior to the virtual line and the most anterior cortices were at least 2 mm away from the line. The straight group included patients in whom the posterior cortices of the most anterior and posterior vertebral bodies from C3 to C6 were located within 2 mm either anteriorly or posteriorly from the line. The sigmoid group included patients in whom the posterior cortex of the most anterior or posterior vertebral body was located at least 2 mm away from the line when at least one posterior cortex of the vertebral bodies was located anteriorly or posteriorly to the line. The kyphosis group included patients in whom the entire posterior cortex of the vertebral bodies from C3 to C6 was located at or posterior to the line and in whom the most posterior vertebral body had its posterior cortex at least 2 mm posterior to the line.
postoperative clinical results. The clinical results were assessed with the modified Japanese Orthopedic Association (JOA) score, visual analog scale (VAS), and neck disability index (NDI) and were compared to analyze the rate of change between preoperative and postoperative values. P The recovery rate was defined as follows: RR5( postopP P preoperative JOA scores/17 preerative JOA scores operative JOA scores)100 [32]. Postoperative radiological results at the final follow-up examinations were compared between groups to obtain the change in range of motion and sagittal alignment. The effect of cervical alignment on JOA, VAS, and NDI and also on change of alignment and change of range of motion (ROM) at the final follow-up examinations was analyzed statistically using the Mann-Whitney U test in paired parameters with SPSS (version 19; SPSS, Inc., Chicago, IL, USA). The results are expressed as the mean6 standard deviation and were considered significant when p value was less than .05.
Results The overall clinical improvement rate of the postoperative modified JOA score was 38.9%. The VAS showed 46.3% decrement and the NDI showed 30.1% decrement in the entire group of patients. Radiological changes
revealed 6.5 (24.7%) decrement in the ROM and 2.0 (18.4%) decrement in the overall cervical alignment at the final follow-up (Table 2). Lordotic versus nonlordotic group according to Toyama classification The lordotic group included 40 patients, and the nonlordotic group included 18 patients. No difference was found for etiology (p5.863), age (56611.3 vs. 59610.6, p5.28), the number of operative segments (4.860.4 vs. 4.860.5, p5.938), modified JOA score (11.064.3 vs. 10.464.5, p5 .653), NDI (21.8614.5 vs. 29.6613.5, p5.136), or VAS (6.063.3 vs. 7.062.0, p5.600), preoperatively. No difference was found regarding radiological parameters ROM (26.3610.9 vs. 24.0612.7, p5.206) and alignment (18.36 9.4 vs. 7.568.6, p5.000), preoperatively. No difference was found between the two groups in terms of the postoperative improvement rate of the modified JOA score (46.3% 640.2% vs. 22.5%661.6%, p5.086), decreasing rate of the VAS (41.6%666.6% vs. 57.0%621.4%, p5.940), or NDI (27.0%634.3% vs. 40.0%621.2%, p5.211), postoperatively. Additionally, no difference was found for the decreasing rate of ROM (25.9%643.4% vs. 17.4%641.6%, p5.427) or sagittal alignment (18.6%661.8% vs. 17.9% 6427.6%, p5.864) based on the radiological evaluation results (Table 3).
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Table 2 Overall patient outcomes Outcome
Preoperation (mean6SD)
Postoperation (mean6SD)
Recovery rate (mean)
Clinical outcomes Modified JOA score VAS NDI
11.463.7 6.363.0 23.7614.5
14.063.3 2.962.1 15.0612.2
38.9% 46.3% 30.1%
Preoperation (mean6SD)
Postoperation (mean6SD)
Decrement (mean)
38.7618.1 14.8610.4 25.3614.5 9.969.6
25.8611.1 13.0612.2 18611.9 8.7611.6
Radiological outcomes ROM Sagittal alignment Segmental ROM Segmental alignment
6.5 2.0 7.7 1.1
JOA, Japanese Orthopedic Association; VAS, visual analog scale; NDI, neck disability index; ROM, range of motion; SD, standard deviation.
Lordotic versus nonlordotic group according to Cobb angle For assessment of the Cobb angle classification, the nonlordotic group included 18 patients and the lordotic group included 40 patients. No difference was found for etiology (p5.638), age (56.3611.6 vs. 58.2610.3, p5.744), number of operative segments (4.860.4 vs. 4.860.5, p5.976), modified JOA score (11.363.9 vs. 10.664.5, p5.830), NDI (22.8615.7 vs. 26.5610.5, p5.378), or VAS (6.46 3.3 vs. 6.062.4, p5.302), preoperatively. No difference was found regarding radiological parameters ROM (27.56 9.0 vs. 21.8613.4, p5.061) and alignment (17.969.9 vs. 2.6610.1, p5.000), preoperatively. No difference was found between the postoperative improvement rate of the two groups in terms of the modified JOA score (32.4% 664.1% vs. 42.5%640.8%, p5.743), VAS (40.5%665.5% vs. 61.1%618.5%, p5.548), or NDI (25.0%633.8% vs. 46.8%615.5%, p5.32), postoperatively. Additionally, no difference was found for the ROM (22.8%644.6% vs. 21.8%639.4%, p51.000) or sagittal alignment (12.7% 638.3% vs. 30.6%6433.4%, p5.440) based on the radiological evaluation results (Table 4).
Discussion To prevent complications, such as cervical instability, progression of kyphosis, and cord compression secondary to scar formation after conventional laminectomy for CSM, OPLL, or multiple intervertebral disc herniations with developmental spinal canal stenosis, many types of laminoplasty techniques have been developed in Japan [9], and laminoplasty is widely used worldwide to treat cervical myelopathy. The strengths of laminoplasty include the following: preservation of the posterior normal structures, such as laminae, ligaments, and muscles; maintenance of some cervical motion, which may prevent the junctional problem that is more common in laminectomy with fusion; short-term immobilization after the surgery; and fewer complications related to the operation [33]. Additionally, several long-term reports indicated that stability persisted for over 10 years after short-term recovery [3–6]. However, laminoplasty is not the only option for the treatment of CSM or OPLL, and surgeons must understand the mechanisms and drawbacks of laminoplasty. The main mechanism of laminoplasty is indirect decompression of anterior lesions, such
Table 3 Outcomes according to Toyama classification Variables Preoperative factor Etiology CSM OPLL Age (y, mean) Number of operated segments More than four segments Less than three segments Recovery rate (mean6SD) Modified JOA score VAS NDI Overall ROM Sagittal alignment
Lordotic group (N540)
Nonlordotic group (N518)
p Value
16 24 56.0
11 7 59.4
.863
25 15
11 7
.938
46.3640.2 41.6666.6 27634.3 25.9643.5 18.6661.8
22.5661.6 57.1621.4 40621.2 17.4641.6 17.96427.6
.086 .940 .211 .427 .864
.28
CSM, cervical spondylotic myelopathy; OPLL, ossification of the posterior longitudinal ligament; JOA, Japanese Orthopedic Association; VAS, visual analog scale; NDI, neck disability index; ROM, range of motion; SD, standard deviation.
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Table 4 Outcomes according to Cobb angle Variables Preoperative factor Pathology CSM OPLL Age (y, mean) Number of operated segments More than four segments Less than three segments Recovery rate (mean6SD) Modified JOA score VAS NDI Overall ROM Sagittal alignment
Lordosis $10 (N540)
Lordosis !10 (N518)
16 24 56.3
11 7 58.2
.638
25 15
11 7
.976
32.4664.1 61.1618.5 46.9615.5 22.8644.6 12.7638.3
42.5640.8 40.6665.5 25.1633.9 218639.4 30.66433.5
p Value
.744
.743 .548 .32 1.00 .440
CSM, cervical spondylotic myelopathy; OPLL, ossification of the posterior longitudinal ligament; JOA, Japanese Orthopedic Association; VAS, visual analog scale; NDI, neck disability index; ROM, range of motion; SD, standard deviation.
as osteophytes, multiple disc herniations, and OPLL. Therefore, posterior shift of the cord is very important. Some authors have reported that the radiological end point of laminoplasty is complete posterior migration of the spinal cord away from the anterior compressive structures [9,22]. Many factors, such as preoperative cervical sagittal alignment, the space available for the spinal cord at cephalad/caudal levels to the decompression, longitudinal distance index, and decompression scope, must be considered in surgical decision making because many reports showed that greater posterior shifts were correlated with better clinical outcomes in laminoplasty [9,19–22]. Now, many authors agree that nonlordotic patients are not good candidates for laminoplasty. They would recommend anterior surgery if the lesion was a short segment, laminectomy with fusion to make a new lordotic alignment to move the spinal cord more posteriorly, or a combination of both procedures. However, in actual clinical situations, it is difficult to select anterior surgery for patients with minor preoperative kyphosis or for elderly patients in poor general condition or with osteoporosis. Additionally, in the authors’ experience, the patients who underwent combined surgery showed better outcomes than expected after the first stage of laminoplasty. Therefore, we have provided evidence for our hypothesis that two possible mechanisms of laminoplasty are equally important. The first mechanism is the well-known posterior shift from the anterior compressing structures, such as protruding multiple discs, osteophytes, OPLL, or a posterior vertebral body from local kyphosis. Many studies have shown a correlation between dorsal migration and clinical outcomes. Baba et al. [26] demonstrated that neurological improvement was associated with posterior cord migration on MRI. Sodeyama et al. [19] found that posterior cord migration of 3 mm on average was critical for good recovery. The second mechanism is the local decompression effect. Impingement of the nerve root or cauda equina
in the lumbar spine of elderly patients can be relieved by posterior decompression without the removal of all the anterior compressing structures, such as multiple-level disc degeneration or osteophytes because of redundancy in nerve tissues [23]. If patients with CSM or OPLL have some degree of redundancy in their spinal cord, local decompression in combination with small posterior migration of the spinal cord would suffice. Also we still do not know the exact amount of posterior cord migration associated with the neurological improvement. We reviewed many articles regarding the correlation between cervical sagittal alignment and clinical outcomes. There are many articles that do not mention or clearly define lordosis. Many studies used Cobb angle to represent the entire cervical sagittal alignment [9,28,29,34]. This measurement might apply to the normal cervical spine, but in the spondylotic cervical spine, Cobb angle would not show the alignment of the subaxial cervical spine. Cobb angle does not highlight the difference among sigmoid curvature, reverse swan-neck deformity, and straight curvature. Although the C2–C7 alignment indicates lordosis, apparent sigmoid curvature is not uncommon. Other measurements, such as the Toyama classification [24], would be more representative of the alignment of the spondylotic cervical spine. Thus, we chose to compare these two different measurement methods. In our study, we excluded patients with severe kyphosis, defined as more than 15 of kyphosis in Cobb angle and subaxial instability. With Cobb measurement, the two groups had similar preoperative factors, such as pathology, age, and number of involved segments. Clinical and radiological outcomes showed no differences according to the definition of lordosis in both groups. According to the Toyama classification, the two groups showed no difference. The results of the current study indicate that cervical nonlordosis may not always be a contraindication for double-door laminoplasty. However, the importance of
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sagittal alignment to surgical results should not be underestimated. Surgeons must consider factors other than cervical sagittal alignment that affect surgical outcomes, such as age, pathology, the number of involved segments, type of OPLL, and instability of the subaxial cervical spine. The limitations of our study included a short-term follow-up (mean 18.7 months), the retrospective nature of the study, the small patient numbers, and the use of only one laminoplasty technique. Most long-term studies suggest that early clinical improvement can be maintained for over 10 years [3–6]. Therefore, we hypothesize that the improvements in our patient groups will also last. However, careful long-term follow-up is necessary because the condition of many patients with OPLL will worsen with time. The incidence of OPLL progression after laminoplasty has been reported to be between 70% and 73%. Younger patients (under 60 years of age) faced the greatest risk of developing OPLL [4,35–37]. In some studies, the progression of OPLL or of kyphosis influenced clinical outcomes beyond 5 years. In the subgroup analyses, there may be some unknown or known factor that will affect the clinical outcomes in nonlordotic patients, such as spinal cord morphology or angulation of the spinal cord based on preoperative MRI [9]. However, the nonlordotic group, according to both definitions, was too small (18 patients) to demonstrate statistically significant differences. A randomized, prospective study of patients with nonlordotic alignment is necessary to assess the clinical efficacy of laminoplasty compared with other procedures, such as anterior decompression and laminectomy with fusion. Finally, most studies of cervical alignment change after laminoplasty focused on unilateral open-door laminoplasty or expansive laminoplasty and its variations. Thus, in our study, double-door laminoplasty, unlike other laminoplasty techniques, was not performed in the same manner in nonlordotic patients. In conclusion, despite nonlordosis cervical sagittal alignment, double-door laminoplasty would be effective for patients with cervical myelopathy because of CSM or OPLL. Furthermore, sagittal alignment is not the absolute and sole factor that surgeons should consider when determining the optimal treatment strategy. References [1] Baisden J, Voo LM, Cusick JF, et al. Evaluation of cervical laminectomy and laminoplasty. A longitudinal study in the goat model. Spine 1999;24:1283–8; discussion 1288–9, 2222. [2] Nowinski GP, Visarius H, Nolte LP, Herkowitz HN. A biomechanical comparison of cervical laminaplasty and cervical laminectomy with progressive facetectomy. Spine 1993;18:1995–2004. [3] Chiba K, Ogawa Y, Ishii K, et al. Long-term results of expansive open-door laminoplasty for cervical myelopathy: average 14-year follow-up study. Spine 2006;31:2998–3005. [4] Iwasaki M, Kawaguchi Y, Kimura T, Yonenobu K. Long-term results of expansive laminoplasty for ossification of the posterior longitudinal ligament of the cervical spine: more than 10 years follow up. J Neurosurg 2002;96(2 Suppl):180–9.
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