Introduction

Degenerative cervical myelopathy (DCM) encompassing Cervical spondylotic myelopathy (CSM) including degenerative disc disease and ossification of the posterior longitudinal ligament (OPLL) are common degenerative spinal disorders that can lead to significant neurological impairment and disability [1]. Cervical laminoplasty (LAMP), a posterior decompression technique designed to preserve the posterior elements of the cervical spine was developed in Japan to reduce problems frequently associated with laminectomy, such as postoperative spinal instability, kyphotic deformity, and formation of the postlaminectomy membrane [2]. LAMP is currently regarded as the gold standard surgical treatment for DCM, particularly for patients presenting without kyphotic deformity or anterior spinal cord compression [3–5]. The surgical procedure of LAMP is generally categorized into two techniques: double-door [6] and open-door LAMP [2]. The clinical outcomes between the two techniques are reported to the comparative [7–9].

A complication specific to cervical LAMP is “lamina closure” which can lead to unfavorable long-term outcomes including cervical kyphotic change and neurological deterioration [10–13]. To prevent lamina closure, recreating a rigid posterior neural arch to obtain bony fusion at the hinge or split spinous process is essential. In conventional double-door LAMP described by Kirita and Miyazaki [6], the laminae were maintained in an open position using stay sutures threaded through the spinous process/the yellow ligament and facet capsule/paravertebral muscle. Subsequently, various materials were introduced to maintain lamina expansion, including hydroxyapatite spacers, suture-anchors, or mini-plates [14].

Suture anchors represent a relatively novel devices for this purpose in the double-door LAMP, offering a simplified technique that requires only embedding the anchor into the lateral mass, thereby avoiding the complex and time-consuming placement of bulkier implants [15,16]. Biomechanical study demonstrated that the use of the suture anchor in cervical LAMP was sufficiently biomechanically tolerable [17]. A pilot study utilizing intraoperative CT demonstrated that the suture-anchor technique maintained laminar expansion more rigidly than the traditional suture-only method in double-door LAMP despite small sample size [18].

Conversely, mini-plate systems were developed in double-door LAMP to provide a more rigid and durable fixation and are currently widely utilized [19–21]. Recently, clip-type plate implants have been reported to exhibit 1.5- 2.0-fold increase in biomechanical strength compared to conventional hydroxyapatite spacers [22]. However, lamina closure can still occur even in the mini-plate system with the incidence of 3.4–13.4% by screw dislodgement or hinge fracture [19,20]. Because the mini-plate systems offer additional increased instrumentation costs, the major concern was whether the mini-plate system provide superior merit than the other alternative techniques.

A recent cost-effectiveness study comparing the mini-plate and hydroxyapatite spacers demonstrated that the surgical costs and incremental cost-effectiveness ratio (ICER) were higher for mini-plates, despite no difference in clinical and radiological outcomes [23]. Although meta-analyses suggested similar clinical results between with and without plate technique [24], high‑quality randomized controlled trials (RCTs) comparing clinical outcomes, safety profiles, and cost‑effectiveness are lacking. Consequently, the true merit of the more expensive plate technique remains unverified.

We hypothesized that the conventional suture-anchor technique yields clinical and radiological outcomes that are non-inferior to the clip-plate technique in the double-door LAMP. The objective of this study is to conduct a multicenter, non-inferiority, RCT to compare the clinical efficacy, radiological outcomes, and safety of double-door laminoplasty using suture-anchors versus clip-plate systems. The study also aims to demonstrate that the conventional technique is non-inferior to the clip-plate procedures, potentially offering a more cost-effective alternative without compromising patient outcomes.

Methods

Trial design

This is a multicenter, open-label, non-inferiority randomized controlled trial. All trial procedures are summarized in Fig 1. Patients will be randomized in a 1:1 ratio to one of two groups: the control group (double-door LAMP using clip-plates) or the experimental treatment group (double-door LAMP using suture-anchors), (Fig 2).

Download:

• PNG
  larger image
• TIFF
  original image

Fig 1. SPIRIT schedule of enrolment, interventions, and assessments.

The schedule outlines the timeline for participant enrollment, interventions, and assessments in the study. SPIRIT, Standard Protocol Items: Recommendations for Interventional Trials; Surg., Surgery; PO., postoperative; Dis., discharge; JOA, Japanese orthopaedic association; NDI, Neck disability index; VAS, Visual analog scale; CSA, Cross-sectional area.

https://doi.org/10.1371/journal.pone.0339103.g001

Download:

• PNG
  larger image
• TIFF
  original image

Fig 2. Study flowchart.

DCM, Degenerative cervical myelopathy; CSM, Cervical spondylotic myelopathy; OPLL, Ossification of the posterior longitudinal ligament.

https://doi.org/10.1371/journal.pone.0339103.g002

Treatment

All surgeries must be supervised by a Japanese Society of Spine Surgery and Related Research (JSSR) certified spine surgery instructor.

Control group: clip-plate technique.

Double-door LAMP using clip-plates is to be conducted as follows. A midline incision and exposure of the C3–C6 laminae, and the spinous processes are trimmed. The laminae are split at the center using a high-speed drill, and bilateral gutters are created at the laminofacet junction. The laminae are gently opened. Small pilot holes are drilled through the opened laminae, and mini-screws are inserted to secure a polyether ether ketone clip-plate (LAMINAclip2, Olympus Terumo Biomaterial Corp., Tokyo, Japan) across the gap by placing over the screw-heads. Although this clip-type plate implant differs from traditional plate systems, it is classified and biomechanically validated as a spinal plate in Japan [22]. This maneuver is performed for at least two levels (Fig 3).

Download:

• PNG
  larger image
• TIFF
  original image

Fig 3. Schema and intraoperative photographs of double-door LAMP using clip-plates.

Mini-screws are set through the opened laminae. Then, the clip-plate is placed over the screw head. LAMP, laminoplasty.

https://doi.org/10.1371/journal.pone.0339103.g003

Experimental treatment group: Suture-anchor technique.

The surgical exposure and laminar splitting are identical to the control group. After opening the bilateral split laminae gently, self-tapping titanium suture anchors (LAMIFIX, Olympus Terumo Biomaterial Corp., Tokyo, Japan) are inserted into the lateral masses, taking care not to penetrate the facet joints. Sutures attached to the anchors are threaded through the yellow ligament and tied to maintain the laminae in an open position. If the stability of the non-fixed lamina is inadequate, alternatively, the additional suture is made between the yellow ligament and the deep fascia. This maneuver is performed for at least two levels (Fig 4).

Download:

• PNG
  larger image
• TIFF
  original image

Fig 4. Schema and intraoperative photographs of double-door LAMP using suture-anchors.

Suture-anchors are inserted into the lateral mass. Then, the sutures are threaded through the yellow ligament and tied in the open position of lamina. LAMP, laminoplasty.

https://doi.org/10.1371/journal.pone.0339103.g004

Endpoints

Primary endpoint.

The Primary endpoint is the recovery rate of cervical Japanese Orthopaedic Association (JOA) score (Table 1) at 1 year postoperatively. The recovery rate calculation formula is as previously reported [2] as follows.

Download:

• PNG
  larger image
• TIFF
  original image

Table 1. Cervical JOA score. Maximum total score:17.

https://doi.org/10.1371/journal.pone.0339103.t001

The primary analysis time point is postoperative 1 year. Results at postoperative 2 years are also presented as a final analysis.

Secondary endpoint.

1. (1). Operative Time and estimated blood loss
2. (2). Minimal Clinically Important Difference (MCID) achievement: the proportion of patients achieving MCID for Cervical JOA score recovery rate, defined as 52.8% according to previous reports [25], at postoperative 1 and 2 years postoperatively in each group.
3. (3). Patient-reported outcomes: health-related quality of life (EQ-5D-5L), Visual Analogue Scale (VAS) for neck pain, upper limb pain, and upper limb numbness, Neck disability index (NDI) at postoperative 1 and 2 years
4. (4). Radiological outcomes:
   • Retention rate: The ratio of the laminar angle at postoperative 1 or 2 years to the angle at 1 week postoperative on CT. A rate < 0.8 indicates lamina closure [13].
   • Hinge fracture: Graded as 0 (none), 1 (ventral cortex fracture), or 2 (complete fracture with collapse) on CT [16] at postoperative 1 or 2 years.
   • Bone union of gutter: Classified as Union (bony bridging), Healed (callus without bridging), or Nonunion on CT [16] at postoperative 1 or 2 years.
   • Cervical spinal alignment: C2-7 angle including the range of motion calculated from flexion and extension lateral views, C-SVA, and T1 slope on X-ray at postoperative 1 and 2 years.
   • Paravertebral muscle: Paraspinal muscle cross-sectional area (CSA) in C4/5 level at postoperative 1 and 2 years on MRI.
   • Postlaminectomy Membrane: Grading of the soft tissue mass posterior to the dural sac on the central slice of the T2 sagittal image [26] and dural sac CSA (C3/4, C4/5, C5/6, C6/7 levels) at postoperative 1 and 2 years.
5. (5). Health Economics: evaluated by ICER. Costs will include direct medical costs (surgery, hospitalization, management of adverse events). Quality-Adjusted Life Years (QALYs) will be derived from EQ-5D-5L scores using a Markov model, with costs and outcomes discounted at 2% annually.
6. (6). Adverse Events: Incidence of intraoperative, early (<30 days), and late (>30 days) complications, using the evaluation criteria from the JSSR database [27] and grading by the Common Terminology Criteria for Adverse Events V.5.0. [28]

Discussion

DCM, including CSM and OPLL, is the most common cause of spinal cord dysfunction in the elderly worldwide. The incidence and prevalence of DCM are estimated at a minimum of 41 and 605 per million in North America. The overall incidence of CSM-related hospitalizations has been estimated at 4.04 per 100,000 person-years, and surgical rates seem to be rising [1]. As the aging population grows, the incidence of DCM-related hospitalizations continues to rise, necessitating effective and sustainable surgical interventions [29], While cervical laminoplasty (LAMP) has become the gold standard for multisegmental DCM, avoiding the kyphotic deformities and membrane formation associated with laminectomy [30], the optimal fixation method for the opened lamina remains a subject of debate.

The double-door LAMP technique proposed by Kirita and Miyazaki has been accepted as an effective compression myelopathy treatment [3,31,32]. While effective, this method has the potential to cause “lamina reclosure,” a complication occurring in 1.8–5.5% of cases that is associated with neurological deterioration [13,16]. The plate system was initially established as an alternative technique to open-door LAMP, providing rigid fixation and simplifying the surgical workflow [33]. It has also been developed in the technique of double-door LAMP and widely spread nowadays [19–22]. However, this mechanical advantage is not without drawbacks; screw back-out and dislodgement, potentially lead to failure of retaining opened lamina [19,20]. Furthermore, the significant cost differential between plates and sutures, with the latter being substantially more expensive, raises critical questions regarding value-based healthcare [29].

This study represents the first large-scale randomized controlled trial (RCT) designed to directly compare the modern clip-plate technique against the conventional suture-anchor technique in double-door LAMP. The primary hypothesis is that the suture-anchor method is non-inferior to the clip-plate system in terms of neurological recovery, as measured by the JOA score. By validating non-inferiority, this trial aims to challenge the assumption that more expensive hardware is associated with superior clinical outcomes. The inclusion of specific exclusion criteria, such as Parkinson’s disease and maintenance dialysis, ensures that the analysis focuses purely on the efficacy of the fixation method for the opened lamina without the confounding variables of severe comorbidities affecting motor function.

Beyond clinical efficacy, this trial addresses several distinct gaps in the current literature. First, safety profiles regarding hinge fractures and bone union will clarify whether the rigid fixation of plates is truly safer than the semi-rigid fixation of anchors. Specifically, the incidence of hinge fractures, a common complication that can lead to palsy or closure, will be meticulously tracked via CT grading [16]. Second, the radiological assessment of the “postlaminectomy membrane” using MRI offers novel insights. Postlaminectomy membrane was reported to occur even after double-door laminoplasty using hydroxyapatite spacers [34]. The actual incidence of postlaminectomy membrane remains unclear after LAMP because no cohort studies have investigated whether LAMP prevents this membrane. Combining analysis of the grading of the mass posterior to the dural sac and cross-sectional area between the Kirita-Miyazaki LAMP with suture-anchors, which involves LAMP without a midline bony roof, and LAMP using clip-plates to form the lamina roof, will yield new insights regarding the incidence of postlaminectomy membrane after LAMP. Finally, the health economic analysis will use ICER. In an era of escalating healthcare costs, demonstrating that a lower-cost technique yields equivalent outcomes could justify changes in insurance reimbursement and surgical guidelines. Japanese insurance data indicates a four-fold cost difference between the implants, highlighting the potential for significant systemic savings [23].

Furthermore, the study employs a minimization randomization method stratified by age, sex, diagnosis, and facility. This rigorous design choice addresses the heterogeneity inherent in DCM populations, ensuring that the treatment groups are balanced regarding critical prognostic factors.

In conclusion, this prospective RCT anticipates establishing high-level evidence regarding the comparative utility of suture-anchors versus clip-plates. By balancing clinical efficacy, safety, and economic sustainability, the findings will empower surgeons and policymakers to make evidence-based decisions in the management of DCM. If the conventional suture-anchor technique proves non-inferior, it validates a cost-effective alternative that maintains high standards of patient care, effectively bridging the gap between traditional surgical principles and modern economic realities.

Supporting information

Acknowledgments

We would like to thank the members of Health Science Research & Development Center (HeRD) at the Institute of Science Tokyo for their assistance in preparing protocol of this clinical research. AI Assistance Statement: Gemini 2.5 pro (Google, CA, USA) was utilized for English proofreading and translation assistance. The authors retain full responsibility for the content.