The posterior cervical muscle-ligament complex is an important structure for maintaining the stability of the cervical vertebrae. It is mainly composed of the spinous processes, supraspinous ligament, interspinous ligaments, and muscle tissues attached to the spinous processes and plays an important role in maintaining the biomechanical stability and physiological curvature of the cervical spine [14]. During open-door laminoplasty, pruning or excision of the spinous processes causes damage to the supraspinous ligament and interspinous ligaments and also removes the spinal attachment points of the posterior cervical muscles. Destruction of the muscle-ligament complex and the loss of muscle attachment points can result in atrophy of the posterior cervical muscles and weakening of the tension band can lead to a loss of cervical curvature and even cervical kyphosis [2,7,9,15]. When performing open-door laminoplasty at C3-7, in order to fully expose the superior border of the C3 lamina and the ligamentum flavum between the C2/3 lamina, partial dissection of thesemispinalis cervicis from the C2 spinous process is required [6]. If this is not reconstructed properly at the end of the operation, iatrogenic muscle injury may result.
The semispinalis cervicis arises from the transverse process of the upper thoracic vertebrae and ends in the C2-5 spinous processes. From a physiological perspective, the most important point is its attachment to C2. Studies have shown that the semispinalis cervicis is the most important posterior cervical extensor muscle, as its contraction accounts for 37% of the total contraction distance in posterior cervical extension [7].Therefore, reconstruction of muscle attachment points and maintenance of mechanical strength of the muscle-ligament complex has become an area of investigation for spine surgeons seeking to improve outcomes after open-door cervical laminoplasty.
Cheng et al [16]. first split the extensor muscle attachment points from the C2 spinous process before opening the laminaeand then reattached the muscles to the C2 spinous process with a suture replacing wire in order to retain the integrity and mechanical strength of semispinalis cervicis. Umeda et al [17]. described C4-6 laminoplasty with C3 and C7 partial laminectomies or C3 laminectomy and C7 dome decompression to maintain the integrity of semispinalis cervicis and the nuchal ligament. Chen et al [18]. first isolated the muscle along the spinous process unilaterally to expose the laminae, and then cut off the muscle-ligament complex together with the spinous process from the root with piezosurgery; after the laminae were opened, the spinous process stump and muscle were reattached to the laminar cortex to preserve the unilateral paraspinal muscle complex. Although the above innovative techniques reconstruct and preserve the integrity of the posterior cervical muscles using different methods, they all increase the complexity of the operation.
To solve this problem, we devised a simpler method of muscle attachment point reconstruction. The current centerpiece titanium plate used to fix the lamina to the lateral mass has a “Z” shape with two holes at each end [5,13,17-19]. Considering that the root of the original spinous process is shifted to the contralateral side after the lamina is opened, it is difficult to achieve reconstruction of the muscle attachment points in the midline. Therefore, we modified the centerpiece titanium plate by appropriately extending the length of the titanium plate on the side of the lamina and adding a hole at the distal end (a total of three holes). During the operation, the medial two holes were used to fix the lamina, while the distal hole was used for reconstruction of the semispinalis cervicis and anchoring and suturing of the cervical extensor muscles.
We found no significant difference in operation time (136.7 min vs. 128.3 min) or intra-operative blood loss (275.9 ml vs. 268.2 ml) between the study groups, indicating that the modified centerpiece titanium plate did not increase the complexity of the operation. In addition, postoperative neurological function significantly improved in both groups and the neurological recovery rates at last follow-up were similar. In addition, there was no significant loss of cervical ROM in either group after surgery. However, cervical curvature and cross-sectional area of the posterior cervical muscles remained well-maintained in group A but significantly decreased in group B.
Retention of cervical motion segments and adequate stability reconstruction are the basis for maintaining normal cervical ROM [14,16]. A “Z-shaped” titanium plate has adequate strength and stiffness to allow stable reconstruction [3,19]. Lateral fixation allows each vertebral body to have independent motion function, so does not cause significant loss of cervical ROM [5,18-19]. Our modified centerpiece titanium plate provides a new attachment point for the posterior cervical muscles, thus avoiding muscle atrophy. In addition, the tension band generated by the posterior cervical muscles can still maintain cervical curvature. Moreover, the supporting point formed at the distal end of the titanium plate at the C3 and C7 segments can also increase the force arm length of the posterior cervical extensor muscles [8,15,20]. Muscle fatigue will not easily occur after frequent cervical flexion and extension, which may explain the mild AS reported by patients in group A.
AS are common after laminoplasty and occur in 6%–60% of patients [21]. The primary manifestations are postoperative neck and shoulder pain accompanied by neck muscle stiffness, tension, discomfort, soreness, or swelling [3,5,7,12,14-15,20]. The mechanisms of postoperative AS development remain unclear but may be related to posterior cervical muscle atrophy, change in cervical curvature or lamina open angle, injury of the muscle-ligament complex, joint capsule damage, cervical instability, or other factors [2-5,7,9,12,14-21]. Spine surgeons have tried to reduce AS by improving surgical technique [2,7,9,12,15], preserving muscle attachment points [7,9,17,22], reconstructing the muscle-ligament complex [18], implanting an appropriate internal fixation device [5], and prescribing postoperative rehabilitation exercises [23] and physical therapy [24]; however, all have achieved various results. In this study, although both groups were fixed with titanium plates with the same mechanical strength, the severity of AS was significantly lower in group A than group B. In addition, we found that the cross-sectional area of the posterior cervical musculature decreased significantly after surgery in group B but not group A. These findings demonstrate that the third hole provided by the modified centerpiece titanium plate can not only reconstruct the integrity of the semispinalis cervicis, but also becomes an effective attachment point to provide mechanical support to the cervical extensor muscles. This effectively maintains the mechanical strength and tension band effect of the posterior cervical muscles, reducing the occurrence of AS.
Our study had several limitations. First, the clinical application time of the modified centerpiece mini-plate was short. Second, the number of samples included in the study was small, and there was a certain bias in the selection and grouping of patients. Third, the follow-up time was short. Therefore, to confirm the clinical efficacy, a large-scale, long-term, multicenter randomized controlled study is required.