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PRIMARY RESEARCH

Anterior Decompression and Fusion Versus Laminoplasty for Cervical Myelopathy Caused by Soft Disk Herniation

A Long-term Prospective Multicenter Study

Koakutsu, Tomoaki MD, PhD*,†; Aizawa, Toshimi MD, PhD; Sasaki, Morichika MD; Sekiguchi, Akira MD, PhD§; Morozumi, Naoki MD; Ishii, Yushin MD; Kokubun, Shoichi MD, PhD; Hashimoto, Ko MD, PhD; Kasama, Fumio MD, PhD; Tanaka, Yasuhisa MD, PhD; Sato, Tetsuro MD, PhD#; Itoi, Eiji MD, PhD; Yamazaki, Shin MD, PhD**

Author Information
doi: 10.1097/BSD.0000000000000986
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Abstract

Cervical myelopathy results from compression of the spinal cord by various degenerative processes of the spine.1 It has been widely treated with anterior decompression and fusion (ADF) or laminoplasty (LP).2,3

ADF can directly remove the compressive pathology from the anterior aspect and provide sufficient decompression even in patients with local kyphosis, without invading cervical posterior ligaments and muscles.4,5 Therefore, ADF using bone grafts or cages with or without plate fixation has been regarded as a gold standard treatment for cervical myelopathy caused by cervical disk herniation (CDH).5–7 However, its drawbacks include anterior-approach–related serious complications such as tracheal edema and recurrent laryngeal nerve injury5,8–12 as well as secondary myelopathy due to adjacent segment degeneration (ASD).6,8,13–17

In contrast, LP enables extensive simultaneous decompression18 for multilevel spinal canal stenosis, and is less surgically invasive and less complication-prone than ADF.4,9,11 Nevertheless, in patients with cervical kyphosis or large anterior compressive pathology, LP may provide insufficient decompression,9,10 leaving residual postoperative neck pain and allowing progression of cervical kyphotic deformity.4,19,20 As a treatment for myelopathy caused by CDH, LP is a technique used to avoid serious anterior surgery-related complications and secondary myelopathy due to ASD. To adopt LP, we must ensure that myelopathy outcomes achieved by LP are at least as favorable as those achieved by ADF. LP without CDH resection has been tried as an alternative and reported to yield short-term outcomes identical to those of ADF.21–23 However, no prospective study has compared the long-term outcomes of LP with those of ADF, including postoperative neck pain, cervical alignment, and range of motion (ROM). Therefore, we prospectively investigated the therapeutic outcomes of ADF versus LP in patients with cervical myelopathy caused by CDH. The 1-year short-term postoperative clinical results have already been reported and indicate no critical difference between the 2 procedures with respect to surgical results or surgery-related factor.24 The 10-year postoperative results are described here.

MATERIALS AND METHODS

Study Design

A long-term prospective multicenter study on the outcomes of ADF versus LP for cervical myelopathy caused by CDH was conducted at 3 hospitals, that is, Tohoku University Hospital, Sendai-Nishitaga Hospital, and Tohoku Rosai Hospital, all of which are affiliated with the Tohoku University Spine Society (TUSS).3 All patients enrolled in the study had cervical myelopathy caused by CDH for <1 year before surgery and no prior history of either cervical injury or surgery or other neuromuscular diseases. CDH was diagnosed on the basis of magnetic resonance imaging (MRI) scans showing that spinal cord compression is due to focal protrusion of an intervertebral disk at the neurologically responsible disk level, and on the basis of plain radiographs or computed tomography scans showing that the focal protrusion is not a posterior spur. Compressive factors other than CDH, number of stenotic levels, and cervical alignment were not considered in participant recruitment and group allocation.

Population and Interventions

Sixty consecutive eligible patients were enrolled in the study (Fig. 1). The first 30 patients (from March 1999 to April 2001) were treated with ADF without instrumentation as described by Kokubun and Sato1 (ADF group). In general, single-level ADF was performed. Exceptionally, in patients with 2-level CDH, or in those with spinal canal stenosis accompanying spinal cord deformation due to compressive factors other than CDH on the abutting segment, 2-level ADF was conducted based on reports that preoperative spinal cord deformation in fusion adjacent segments is a risk factor for secondary myelopathy.14,17 The next 30 patients (from September 2001 to July 2003) were treated with double-door LP as described by Kurokawa25 with use of hydroxyapatite ceramic spacers as described by Kokubun and Sato1 (LP group). As a general rule, C3–C6 LP was performed to provide extensive decompression while conserving the C7 spinous process and attached muscles and ligaments. The exception was C3–C7 LP performed for C6/C7 disk herniation. We aimed to achieve decompression with posterior shift of the spinal cord, as had been achieved in cases of compression caused by ossification of the posterior longitudinal ligament26 even if CDH was not reduced spontaneously. The extent of LP was always C3–C6 or C3–C7, even if CDH was the only compressive lesion and the number of stenotic vertebrae varied.

FIGURE 1
FIGURE 1:
Flow chart illustrating the trial profile. ADF indicates anterior decompression and fusion; LP, laminoplasty.

Postoperative Treatment

All patients were treated in the same manner postoperatively. They were allowed to sit up the day after surgery and required to wear a plastic cervical collar for a month.

Outcome Assessment

Before surgery, the severity of myelopathy was evaluated with use of a scoring system proposed by the Japanese Orthopaedic Association (JOA score), and the severity of neck pain was evaluated by using our own point-based criteria24: 0 points for no pain; 1 point for occasional mild pain requiring no analgesics; 2 points for incessant mild pain or occasional intense pain requiring analgesics; 3 points for incessant intense pain. Lordosis angle, ROM of the cervical spine, and the anteroposterior diameter of the canal at the disk level of herniation were measured on plain x-ray films, which were taken with a tube-film distance of 1.8 m. Lordosis angle was defined as the angle between the lines drawn parallel to the lower margins of the C2 and C6 bodies, respectively, and ROM was defined as the difference between the lordosis angle in flexion and lordosis angle in extension. Discography was performed in all patients, and the canal occupancy ratio at maximum compression by CDH was calculated on lateral x-rays (Fig. 2)24 because the 0.5-Tesla MRI scanner of that time produced poor resolution images. Age at surgery, sex, disk level of herniation, operative time, blood loss during surgery, and surgery-related complications were recorded.

FIGURE 2
FIGURE 2:
Occupancy ratio. The percentage of the spinal canal occupied by the herniated disk (%)=A/(A+B)×100. M1, M2: the mid-point of the posterior surface of each of 2 adjacent vertebral bodies; L1, L2: site on the anterior surface of the lamina of each of 2 adjacent vertebral bodies; P: the site of peak soft-disk herniation; A: the size of the soft disk herniation; B: the space available for the spinal cord.

One and 10 years after surgery, we assessed JOA score, recovery rate,27 and the severity of neck pain in both groups, and the severity of donor site pain in the ADF group alone. Both neck pain and donor site pain severity were evaluated using our own point-based criteria.24 Other parameters including JOA score, recovery rate, neck pain, lordosis angle, and ROM of the cervical spine were measured in the same manner as preoperatively, at 1 and 10 years after surgery in both groups. Bone fusion was assessed on plain x-ray films 1 year after surgery in the ADF group. ASD was assessed on plain x-ray films 10 years after surgery in the ADF group. ASD was defined as ≥30% narrowing of the disk space,16 or new anterior or posterior listhesis of >2 mm compared with before surgery.15 A similar assessment was performed in the LP group. The regression of CDH was evaluated on MRI in the LP group. The occupancy ratio (Fig. 2)24 was measured on a T1-weighted sagittal MRI and then compared before and after surgery. A >50% reduction in occupancy was regarded as “CDH reduction.”24

Statistical Analysis

Continuous variables are expressed as mean±SD for normally distributed data. Differences between groups were evaluated by the Student t-test for continuous variables, and the χ2 test for discrete or categorical variables using JMP Pro 13.2.1 (SAS Institute Inc., Cary, NC). A P-value <0.05 was considered significant.

Ethical Aspects

The protocol of this study was approved by the Institutional Review Board at each hospital. All patients were fully, preoperatively informed about the study before giving their written consent.

RESULTS

Characteristics of the Study Population

We analyzed the data of 22 ADF patients and 20 LP patients (follow-up rate: 70%) who had completed the follow-up examination scheduled 10 years after surgery (Fig. 1). The reasons for loss to follow-up were (1) patient’s refusal due to improvement of myelopathy, too busy, or medical cost (13 cases), and (2) disappearance, migration, or death after 2011 Great East Japan Earthquake (5 cases). Clinical characteristics are shown in Table 1. The baseline characteristics of the patients were similar between the 2 groups. We performed single-level ADF in 15 patients, 2-level ADF in 7 patients (2 with double herniation, and 5 with spinal cord deformation due to compressive factors other than CDH on the abutting segment), C3–C6 LP in 19 patients, and C3–C7 LP in 1 patient. There was no statistically significant difference in operative time: 122±25 min in the ADF group and 123±25 min in the LP group (P=0.873). The amount of blood loss during surgery was significantly less in the LP group (68±54 mL) than in the ADF group (119±91) (P=0.035).

TABLE 1 - Clinical Factors of the Groups (Mean±SD)
Parameters ADF (n=22) LP (n=20) P
Age at surgery (y) 50±9 (38–59) 53±12 (33–71) 0.495
Sex Male 14, Female 8 Male 13, Female 7 0.927
Disk level of herniation* 0.631
 C3–C4 2 2
 C4–C5 8 8
 C5–C6 10 10
 C6–C7 4 1
AP canal diameter (mm) 13.2±1.2 13.3±1.4 0.755
Developmental stenosis† 9 (41%) 7 (35%) 0.693
Occupancy ratio (%) 47.7±10.5 54.0±8.4 0.044
Operative time (min) 122±25 123±25 0.873
Blood loss (mL) 119±91 68±54 0.035
*Double herniation was present in 2 patients in the ADF group and in 1 patient in the LP group.
†AP canal diameter≤12 mm.
ADF indicates anterior decompression and fusion; AP, anteroposterior; LP, laminoplasty.

Surgical Complications

Surgical complications including postoperative C5 palsy, anterior-approach–related complications such as tracheal edema, dysphagia, and recurrent laryngeal nerve injury did not occur. Reoperation was not required for patients in either group within 1 year of surgery.

Neurological Results

The severity of myelopathy (JOA score) before and after surgery and the recovery rate are shown in Table 2. One patient from the ADF group underwent LP for secondary myelopathy due to ASD 2 years after ADF, and was discarded from statistical analysis. There was no statistically significant between-group difference in preoperative and postoperative JOA scores or the recovery rate.

TABLE 2 - Neurological Evaluation of the Groups (Mean±SD)
Parameters ADF (n=21)* LP (n=20) Mean Diff (95% CI) P
Japanese Orthopaedic Association score (points)
 Preop. 9.1±2.6 9.2±2.6 −0.1 (−1.7 to 1.6) 0.945
 Postop. 1 y 15.1±1.6 15.1±2.1 0.0 (−1.2 to 1.3) 0.946
 Postop. 10 y 14.8±1.9 14.2±1.5 0.7 (−0.4 to 1.8) 0.232
Recovery rate (%)
 Postop. 1 y 72.5±22.3 74.5±21.6 −2.0 (−16.5 to 12.5) 0.779
 Postop. 10 y 69.4±25.6 59.0±26.2 10.5 (−5.9 to 26.8) 0.204
*In 1 patient in the ADF group requiring additional surgery because of secondary myelopathy was discarded from statistical analysis.
ADF indicates anterior decompression and fusion; CI, confidence interval; Diff, difference; LP, laminoplasty; Postop., postoperative; Preop., preoperative.

Radiologic Results

Radiologic evaluation of the groups is shown in Table 3. The lordosis angle was significantly smaller 10 years after surgery than preoperatively in each group (ADF group, P=0.015; LP group, P=0.043) but there was no statistically significant difference between the 2 groups. ROM was significantly reduced 10 years after surgery in both groups (ADF group, P<0.001; LP group, P<0.001) but without a significant between-group difference.

TABLE 3 - Radiologic Evaluation of the Groups (Mean±SD)
Parameters ADF (n=21)* LP (n=20) P
Lordosis angle (deg.)
 Preop. 14.5±9.4 7.5±10.1 0.034
 Postop. 1 y 10.2±9.7 3.7±11.0 0.071
 Postop. 10 y 7.5±2.2 3.2±10.3 0.182
Range of motion (deg.)
 Preop. 47.6±10.8 34.7±12.2 0.001
 Postop. 1 y 36.2±7.5 30.3±14.1 0.127
 Postop. 10 y 26.9±1.9 22.2±10.0 0.101
Bone fusion 21 (100%)
C2–C3 interlaminar fusion 6 (30%)
Adjacent segment degeneration 14 (67%) 9 (47%)
Reduction of herniation 20 (100%)
New herniation 5 (25%)
*In 1 patient in the ADF group requiring additional surgery because of secondary myelopathy was discarded from statistical analysis.
ADF indicates anterior decompression and fusion; LP, laminoplasty; Postop., postoperative; Preop., preoperative.

Bone fusion was achieved in all patients in the ADF group. ASD was observed in 14 patients (67%) 10 years after surgery in the ADF group. Segment degeneration was observed in 9 patients (47%) in the LP group. Furthermore, spontaneous interlaminar fusion at C2–C3 was observed in 6 patients (30%). In postoperative MRI, CDH was reduced in 12 patients (60%) of the LP group 1 year after surgery and in all patients of the LP group 10 years after surgery. New disk herniation was detected at a different disk level in 5 patients of the LP group (25%) on MRIs 10 years after surgery, but none of the patients showed neurological deterioration owing to extensive posterior decompression. Representative cases are shown in Figures 3 and 4.

FIGURE 3
FIGURE 3:
A 51-year-old male patient. Preoperative plain x-ray (A) showed developmental stenosis and dynamic stenosis at C3–C4. Lordosis angle was 20 degrees. Preoperative MRI sagittal view (B) demonstrated soft disk herniation at C3–C4. Plain x-ray 1 year after C3–C4 ADF (C) showed bone union. MRI obtained 1 year after C3–C4 ADF (D) showed good decompression of the spinal cord. Plain x-ray (E) and MRI (F) 10 years after C3–C4 ADF. Lordosis angle was 4 degrees. Local kyphosis was not observed at C3–C4. Degenerative change in the nonfusion segment had advanced. Japanese Orthopaedic Association score was 10 points before surgery but 17 points 10 years after surgery. Both neck pain and donor-site pain were 0 points; therapeutic outcome was excellent. ADF indicates anterior decompression and fusion; MRI, magnetic resonance imaging.
FIGURE 4
FIGURE 4:
A 51-year-old female patient. Preoperative MRI sagittal view (A) and axial view (B) demonstrated soft disk herniation at C5–C6 (white arrows). MRI obtained 1 year after C3–C6 laminoplasty showed no reduction of herniation with residual deformity of the spinal cord (white arrows) (C, D). Ten years after surgery, herniation at C5–C6 was clearly reduced (white arrows) (E, F). New disk herniation at C4–C5 was observed, but deformity of the spinal cord was minimum (gray arrows) (E, G). Japanese Orthopaedic Association score was 9, 16, and 16 points before, 1 year after, and 10 years after surgery, respectively. No neurological deterioration had occurred.

Donor Site Pain and Neck Pain

The donor site pain score in the ADF group was 0 point in 15 patients (68.2%) and 1 point in 7 patients (31.8%) 1 year after surgery; 0 point in 20 patients (90.9%) and 1 point in 2 patients (9.1%) 10 years after surgery. Evaluation of neck pain is shown in Table 4. Neck pain was significantly more severe in the LP group than in the ADF group at 1 and 10 years after surgery, respectively. Neck pain was significantly worse at 10 years after surgery than at 1 year after surgery in the LP group (P=0.016) but not significantly changed between 1 and 10 years after surgery in the ADF group (P=0.25).

TABLE 4 - Evaluation of Neck Pain (Points)
Pain Score ADF (n=21)* LP (n=20) P
Preop. 0.075
 0 (none) 16 9
 1 (sometimes mild) 3 9
 2 (always or sometimes severe) 2 2
Postop. 1 y 0.041
 0 (none) 17 10
 1 (sometimes mild) 4 10
 2 (always or sometimes severe) 0 0
Postop. 10 y 0.003
 0 (none) 15 5
 1 (sometimes mild) 6 14
 2 (always or sometimes severe) 0 1
*In 1 patient in the ADF group requiring additional surgery because of secondary myelopathy was discarded from statistical analysis.
ADF indicates anterior decompression and fusion; LP, laminoplasty; Postop., postoperative; Preop., preoperative.

DISCUSSION

This study is the first one to report the prospective long-term outcomes of ADF versus LP for cervical myelopathy caused by CDH. At 10 years after surgery, the improvement in myelopathy was identical between the ADF and LP groups; in addition, no statistically significant difference was observed in cervical lordosis or ROM between the 2 groups. In 1 patient from the ADF group, revision surgery was conducted because of myelopathy recurrence in the adjacent segment. Postoperative neck pain was significantly more severe in the LP group.

Since the report by Robinson and Smith28 of an anterior spinal fusion technique for cervical disk disease in 1955, ADF has conventionally been used with stable outcome for cervical myelopathy caused by CDH.5–7 However, complications related to anterior approach and secondary myelopathy due to ASD are its drawbacks.5,8–12 The latter is a particular concern for patients with developmental and/or multilevel canal stenosis. Its frequency has been reported as 5%–19% at 4–10 years after surgery.6,8,13,24,29 In this study, anterior-approach–related complications were not observed after 1-level or 2-level ADF. The revision rate 10 years after primary surgery was 5% which indicates the outcomes in our report were similar to or better than previously reported.8,13,29 From the results of this study, ADF is a good indication for single-level CDH in patients without developmental or multilevel canal stenosis.

In the 1970s and 1980s, LP was developed as a technique for simultaneous multilevel decompression of cervical spinal cord compression caused by ossification of posterior longitudinal ligament or cervical spondylosis.25,30 LP is less surgically invasive and less complication-prone than multilevel ADF because the procedure is designed to handle nearly normal cervical posterior elements rather than the anterior elements.4,9,11 Therefore, the number of LPs performed in Japan has greatly increased over the last few decades.3 To avoid anterior-approach–related serious complications and secondary myelopathy, LP without CDH resection was tried and reported to yield short-term outcomes identical to those of ADF.21–23 In this study, no secondary myelopathy was noted and no revision surgery was needed 10 years after primary surgery, though new herniation developed at other disk levels in 25% of LP-treated patients.

Reduction of cervical lordosis and ROM is a postoperative problem after LP.20,31 Intraoperative damage to the cervical posterior muscles, ligaments, and zygapophyseal joints may play a key role in the pathogenesis of reduced lordosis.20,32 In this study, rates of postoperative cervical lordosis were slightly better 10 years after ADF than after LP but the between-group difference was not significant. Not only the lack of posterior soft tissue invasion in ADF but also the degenerative processes of the cervical spine seem to affect the postoperative reduction of cervical lordosis. ROM was significantly reduced 10 years after surgery in both groups but without a significant between-group difference. Postoperative segment degeneration in both groups and spontaneous interlaminar fusion after LP seem to affect the postoperative reduction of ROM.

Axial neck pain after LP is also a noticeable complication because it interferes with daily activities.19 In addition, it does not decrease over the long term.2,20 It has been reported to occur in 60%–80% of patients after LP.31 In the present study, 75% of patients complained of neck pain 10 years after LP, whereas 80% of patients had no neck pain 10 years after ADF. Moreover, neck pain was significantly worse 10 years after LP than 1 year after LP. Nerve roots, deep extensor muscles that have been dissected from the spine and denervated, and zygapophysial joints that have been partially destroyed to make gutters have been considered to be possible sources of axial pain occurring after LP.19 Although it is unclear, the cause of residual axial neck pain after LP may be attributed to the irreversible damage to the nuchal musculature during surgery.4 From the results of this study, C3–C6 LP (with C2, C7 dome osteotomy, if necessary) to preserve the C7 spinous process and attached muscles and ligaments could be a procedure of choice for CDH associated with developmental and/or multilevel canal stenosis to avoid secondary myelopathy. While it may reduce postoperative neck pain, limited LP (eg, C4–C5 LP for C4–C5 CDH) is associated with a higher risk of secondary myelopathy. The long-term results of skip laminectomy,31 cervical microendoscopic LP,32 or other new surgical techniques which reduce invasion of the posterior soft tissues may clarify the relationship between the axial neck pain and the reduction of cervical lordosis and posterior muscle damage.20 Assessment of the clinical outcomes of minimally invasive posterior decompression surgery should include not only reduction in pain and preservation of cervical lordosis but also neurological outcomes including recurrence of myelopathy.

Interestingly, CDH reduction was confirmed in all the patients 10 years after LP but only in 60% of the patients 1 year after LP. Spontaneous regression of disk herniation has been reported in the cervical spine as well as the lumbar spine.21,22 Most CDHs contain cartilaginous endplate fragments that resist absorption.33,34 CDHs are mostly located between the deep and superficial layers of the posterior longitudinal ligament and rarely protrude into the epidural space.34 Therefore, it may take a longer time for resorption of CDH. From our present study, it is unclear when the volume of CDH decreases during the 1-year to 10-year period after LP. In cases of giant CDH without spontaneous reduction after LP, posterior decompression will either be achieved by shifting the spinal cord posteriorly18,26,27 or become insufficient.9,10 If the initial recovery in myelopathy is inadequate, additional ADF may be considered because residual anterior spinal cord compression may reduce myelopathy recovery.10

This study had the following limitations: (1) The number of patients was small. We guess that we should have recruited more patients, based on the estimation of required sample size. (2) This investigation had a before-and-after and not a prospective, randomized design and therefore relied on an inferior quality of evidence. (3) Patient-based evaluation was lacking, so that it is unknown how much subjective symptoms, such as neck pain, affected patients’ activities of daily living and satisfaction with the outcomes of operative techniques, all resulting in similar improvement in myelopathy.

In conclusion, ADF and LP achieved similarly favorable outcomes of cervical myelopathy caused by CDH, although sample size was small. ADF has the disadvantage of recurrence of myelopathy caused by ASD, and LP has the disadvantage of residual neck pain and the advantage of no reoperation for secondary myelopathy. LP will become a treatment option for CDH-related cervical myelopathy associated with developmental and/or multilevel canal stenosis when a larger-scale study provides proof of its efficacy.

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Keywords:

anterior decompression and fusion; cervical spine; laminoplasty; myelopathy; soft disk herniation

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