1 Introduction

Laminoplasty is known to provide long-term neurological improvement in cases of cervical myelopathy.^1,2 However, this procedure can sometimes lead to undesirable outcomes, such as C5 palsy, axial pain, and the progression of cervical kyphosis. The closure of the opened lamina resulting from cervical kyphosis progression has been associated with poor clinical outcomes.^3–6 Several methods, including bone grafts, anchoring screws, plates, and hydroxyapatite spacers, have been developed to prevent the closure of the lamina.

In double-door laminoplasty, the lamina is sutured to the paravertebral muscle to keep the lamina open (as described by Kirita and Miyazaki); the procedure has been adopted in several institutions.^4,7 Although lamina closure is widely known, only case reports of lamina closure reoperations using this method are available.⁸ Restenosis by lamina closure may have an adaptable range, and cases of recurrent myelopathy may be rare. In addition, some patients with restenosis may not have been reported. The reoperation rate of double-door laminoplasty using local or artificial bone structures has been analyzed,⁹ but not using the suture method. In this study, we investigated the incidence and clinical features of reoperation for myelopathy recurrence in patients who underwent double-door laminoplasty with the suture method.

2 Materials and methods

2.2

2.2 Surgical procedure

Double-door laminoplasty was performed using a technique modified from that described by Kirita and Miyazaki.⁷ First, the center of each lamina was divided to create bilateral grooves using a high-speed air-burr drill. Then, the lamina was opened bilaterally and kept open using sutures on the deep fascia of the paraspinal muscles. We did not graft the local bone in addition to the opened lamina; this step differed from the original method (Fig. 1). Laminoplasty was performed in the C3–7 range, depending on the case (The operated sites included 20 cases of C3-7, 7 cases of C4-7, 94 cases of C3-6, and 48 cases involving different cervical levels). The semispinal muscles of C2 and C7 were preserved to the maximum extent possible in all cases.

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Fig. 1 The opened lamina is simply sutured to the paraspinal muscles (as highlighted by black arrows) with non-absorbable threads. A) The lamina was opened bilaterally. B, C) The lamina was kept open using sutures on the ligamentum flavum and the deep fascia of the paraspinal muscles.

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2.3

2.3 Clinical and radiological evaluation

We investigated the reoperation rate for recurrence of myelopathy with lamina closure. Spinal cord compression was confirmed in all patients by magnetic resonance imaging (MRI). The risk factors for reoperation by lamina closure (RLC) were compared with those in patients without reoperation (non-RLC), including age, history, and radiological findings, which included cervical alignment, C2–7 lordosis, cervical sagittal vertical axis (C-SVA), and C7 slope.⁴ The two groups were compared using preoperative radiographs from the initial surgery. The results were evaluated by two independent orthopedic surgeons. Radiological findings were obtained in the neutral position. Cervical alignment was categorized into four types: lordosis, straight, sigmoid, and kyphosis. C2–7 lordosis was evaluated by drawing parallel lines extending from the lower endplate of the most-superior vertebral level to the lower endplate of the most-inferior vertebra. The C-SVA was calculated using the horizontal distance between the postcranial corner of the C7 vertebral body and the plumb line drawn from the centroid of C2. The C7 slope was defined as the line drawn across the cranial endplate of the C7 vertebra and the horizontal axis. In patients who underwent RLC, the opening rate of the opened lamina angle at the time of reoperation was additionally measured (Fig. 2). The opening rate was defined as the ratio of the lamina angle at the time of reoperation to that before the initial surgery. The lamina angle was defined as the angle between the lamina and the posterior wall of the vertebral body on a computed tomography axial image at the most stenotic site.⁴

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Fig. 2 The opening rate is measured by the axial view of the computerized tomography. 1) Preoperative state. 2) State before reoperation at the site of the most severe spinal stenosis.

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3 Results

3.3

3.3 Comparison of reoperation between surgeries with and without lamina closure

The RLC cases had more neuromuscular or psychiatric disorders (60% [3/5] vs. 2% [4/164]; p < 0.001), kyphotic alignments (60% [3/5] vs. 10% [16/164]; p < 0.001), and cases with less than −10° of C2–7 lordosis (60% [3/5] vs. 7% [11/164]; p < 0.001) than the non-RLC cases (Table 2). The groups had no significant differences in age, C-SVA, or C7 slope. Kyphosis progressed in all patients before reoperation; the opened lamina was closed more before the initial surgery except in one case (Fig. 3). The one case showed inadequate spinal canal enlargement; the spinal cord was compressed into the anterior vertebral body by progressive excessive kyphosis. Details of the reoperation cases are presented in Table 3. All the patients had at least one risk factor.

Table 2 Risk factors of reoperation due to lamina closure.

Risk factors	RLC (n = 5)	Non-RLC (n = 164)	P value
Age >65 years, n (%)	2 (40)	104 (63)	0.28
Alignment (kyphosis), n (%)	3 (60)	11 (7)	<0.001
C2–7 lordosis < −10°, n (%)	3 (60)	6 (4)	<0.001
C-SVA >40 mm, n (%)	1 (20)	25 (15)	0.77
C7 slope >30°, n (%)	0 (0)	49 (30)	0.15
Cerebral palsy and/or mental illness, n (%)	3 (60)	4 (2)	<0.001

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Fig. 3 Left: the C2–7 lordosis. Right: the opening rate of opened lamina in the reoperation cases by the recurrence of myelopathy.

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Table 3 Detail of reoperation cases due to lamina closure.

Case	Age	Sex	Dx	Surgical Site	Duration (days)	Comorbidity	C2–7 lordosis before initial surgery (deg)	C2–7 lordosis before reoperation (deg)	Opening rate (%)
1	63	M	CSM	C4-6	456	Mental depression	34	−42	−16
2	50	F	CSM	C4-7	328	Cerebral palsy	16	−15	−3
3	43	M	OPLL	C3-6	1408	Diabetes	−11	−22	−7
4	66	M	CSM	C3-7	756	Asthma	−20	−70	−29
5	82	F	CSM	C3-7	19	Cerebral palsy	−48	−60	10

4 Discussion

Laminoplasty was developed to prevent post-laminectomy membrane and preserve the posterior structure. Surgical methods are divided mainly into open-door and double-door laminoplasties. Lamina closure has been reported mainly in open-door laminoplasties. Satomi et al. reported that 1.5% (3/204) of reoperation cases are caused by postoperative lamina closure during open-door laminoplasty.¹⁷ Matsumoto et al. reported that 35% of patients developed lamina closure after open-door laminoplasty, but the lamina closure did not significantly affect the surgical outcome 5 years after surgery.^5,18 In cases with kyphosis progression after surgery, Tamai et al. reported that patients whose surgeries used anchor methods showed significantly more lamina closure than those whose surgeries used spacer methods.⁶ Reports of lamina closure in double-door laminoplasty are limited. Sakai et al. reported that lamina closure occurred in patients who underwent laminoplasty using the suture anchor method; patients with lamina closure showed worse surgical outcomes than those with non-lamina closure.⁴ Regardless of whether the open-door or double-door method was used, all reports agreed that lamina closure occurred in patients with kyphosis progression if a bone graft, spacer, or plate between the gap of the opened lamina was not used.

Despite numerous reports on lamina closure, reoperation for restenosis caused by lamina closure is extremely rare. Recently, the reoperation rates of double-door laminoplasty using bone or artificial bone structures have been reported. The total rate of reoperation, excluding perioperative complications, was 1.6% (10/623), and the rate of restenosis cases was 0.2% (1/623), excluding the cases of radiculopathy and enlargement of ossification from the reoperation cases, at the average 6-year follow-up (minimum 2-year follow-up).⁹ Regarding double-door laminoplasty using suture methods, we found case reports of restenosis caused by lamina closure; however, the reoperation rate has not been reported. In our study, the reoperation rate was 4.1%; restenosis was 3.0% at the average 6-year follow-up (minimum 2-year follow-up). Reoperation was performed mainly due to restenosis with lamina closure.

We investigated the risk factors associated with cervical kyphosis. A history of neuromuscular disease or mental depression has been associated with dropped head syndrome epidemiology.¹⁹ However, the clinical outcomes of laminoplasty in patients at risk of drop-head syndrome have not been reported. Our analysis found that careful follow-up after laminoplasty is needed in patients with a risk past history of kyphosis progression, even those with cervical lordosis. Regarding radiological findings associated to the kyphosis progression, we found no significant differences in C-SVA and C7 slope, except in cervical alignment and C2–7 lordosis. C2-7 lordosis is not only a kyphosis progression factor after laminoplasty, but also a factor contributing to poor surgical outcomes. Several reports have not included excessive cervical kyphosis as an indication of laminoplasty.²⁰ The spinal cord does not adequately shift posteriorly after laminoplasty in patients with kyphosis; kyphosis is a factor in poor surgical outcomes. The inclusion criteria for the kyphosis angle for laminoplasty differed among institutions: −5° to −15° of C2–7 lordosis.^4,21 Our study did not exclude patients based on cervical angle, and the decision regarding the surgical method depended on the surgeon. Kyphosis is not the sole factor in selecting fusion surgery; non-fusion surgery is often performed in patients with cervical kyphosis, considering surgical invasiveness and preservation of cervical motion. We performed laminoplasty in nine patients with less than −10° of C2–7 lordosis; 33% (3/9) of the patients needed reoperation. Whether reoperation could be avoided if another non-fusion method (laminectomy or lamina spacer) was selected is unclear; however, the high reoperation rate for lamina closure showed that the suture method might be better to avoid in patients with kyphosis. Of the five cases with reoperation, three had kyphosis >10°, and two cases with lordosis had a history of neuromuscular or psychiatric disease. Our relatively high reoperation rate could have been influenced by the indications for laminoplasty and the surgical method with the risk of lamina closure.

In the patients with preoperative C2–7 lordosis more than −5°, approximately 95% kept the lamina opening in double-door laminoplasty using suture methods.⁴ Our study also found no cases of reoperation in patients with no risk factors. Double-door laminoplasty using simple sutures is cost-effective and carries no risk of implant-related complications. Lamina spacers may reduce the risk of lamina reclosure, but they may also increase the risk of spacer dislocation and dural injury.^22,23 Therefore, we believe that patients without risk factors for kyphosis progression are good candidates for double-door laminoplasty using simple sutures. However, our study included only reoperation cases and could not investigate clinical outcomes, including the JOA score. The mid- and long-term outcomes of double-door laminoplasty using suture methods have not yet been reported; therefore, further research is required to confirm this hypothesis.

Our study had some limitations. First, this study was retrospective, and the surgical outcomes depended on patient selection. The reoperation cases included patients with cervical kyphosis or risk factors for kyphosis progression, including cerebral palsy or depression. Controversial indications for laminoplasty increase the reoperation rate. Second, three patients with recurrence did not undergo surgery. The cases showed restenosis on MRI; however, reoperation was avoided, given the patient's general condition and difficulty estimating the surgical effect. Recurrence without surgery lowers the reoperation rate. Third, the number of reoperation cases was small, with only five cases, which limited the statistical reliability of the comparisons. Finally, we did not investigate surgical techniques in detail. The technique used to prevent kyphosis and lamina reclosure (preservation of the semispinalis muscle and sewing the lamina to the paravertebral muscle) would influence the progression of kyphosis and lamina closure.

5 Conclusions

The rate of reoperation for recurrence of myelopathy after a double-door laminoplasty with the suture method was 3.0%. The suture method might be avoided to lower the risk of lamina closure in patients with a history of neuromuscular or psychiatric disease or C2–7 lordosis less than −10°.

Research ethics and patient consent

This study was approved by the Kyushu University Institutional Review Board (January 11, 2022; IRB approval number: M22097-00).

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Role of each author

Hideki Jimbayashi, MD; Conceptualization, Validation, Formal analysis, Investigation, Data Curation, Writing - Original Draft Keiichiro Iida, MD, PhD; Conceptualization, Validation, Formal analysis, Investigation, Data Curation, Writing - Review & Editing Kazu Kobayakawa, MD, PhD; Validation, Formal analysis Hirokazu Saiwai, MD, PhD; Validation, Formal analysis Kenichi Kawaguchi, MD, PhD; Validation, Formal analysis Yoshihiro Matsumoto, MD, PhD; Validation, Formal analysis Yasuharu Nakashima, MD, PhD; Formal analysis, Supervision.