Comparative Study of Imaging Parameters between a New Cervical Full Lamina Back Shift Spinal Canal Enlargement Technique and Single Open-door Laminoplasty for Multisegment Cervical Spondylotic Myelopathy

Purpose To provide imaging evidence of the feasibility and clinical ecacy of a new full lamina back shift spinal canal enlargement technique by comparing its imaging parameters to those of single open-door miniature titanium plate internal xation. Methods A retrospective analysis was conducted on 64 patients with multisegment cervical spondylotic myelopathy caused by cervical stenosis. Of these, 32 underwent the new full lamina back shift spinal canal enlargement technique (observation group), and 32 underwent single open-door miniature titanium plate internal xation (control group). The CT data of both groups were imported into Mimics 17.0 software to measure the median sagittal diameter and cross-sectional area of the spinal canal. Photoshop CS5 was employed to measure the drift distance of the spinal cord on MR images to perform a comparative study of the imaging parameters from the two groups. Results The T2-weighted MR images in both groups showed continuous recovery of the cerebrospinal uid signal in the C3–C7 range. The new full lamina back shift spinal canal enlargement technique was signicantly superior to single open-door miniature titanium plate internal xation with respect to the spinal canal cross-sectional area and the median sagittal diameter (P<0.05). No signicant difference was detected in the drift distance of the spinal cord between the two groups (P>0.05). Conclusion The new full lamina back shift spinal canal enlargement technique achieved a thorough spinal canal decompression effect on imaging while ensuring a reasonable spinal drift distance and few surgical complications. The clinical curative effect of the new technique was precise.


Introduction
Multisegment cervical spondylotic myelopathy is a neck condition that arises from degenerative changes in the cervical region of the spine. Cervical spinal stenosis resulting from multisegment disc herniation, ligament hypertrophy, and ossi cation hyperplasia compresses or stimulates the cervical spinal cord as well as the associated blood vessels, leading to sensory, motor, and re ex dysfunction in the spinal nerves. After onset, the progression of cervical spinal spondylosis is associated with the development of complications. Several investigators [1][2] have chosen posterior cervical surgery for treatment owing to its relative safety, effectiveness, and low rate of spinal cord injury during surgery.
In 1977, Hirabayashi et al. [3] invented a single-door spinal canal enlargement laminectomy, which directly relieved posterior spinal cord compression and expanded the sagittal diameter of the cervical spinal canal. Simultaneously, the "bowstring principle" formed by physiological cervical lordosis in the cervical spinal cord was used to make the spinal cord drift backward to achieve an indirect decompression effect on the anterior and ank side of the spinal cord [4]. Subsequently, additional studies on posterior cervical surgery, the development of internal xation technologies, and various improved posterior cervical surgeries have continued to emerge. The study by O'Brien et al. [5] showed that the use of a titanium miniplate to x the lamina could provide strong support, protecting the dura mater effectively with improved stability. Single open-door miniature titanium plate internal xation is effective and reliable. However, injury to the posterior cervical muscle ligament complex can be large, and the spinous process can deviate from the midline, which would disrupt the stability of the cervical spine and cause axial symptoms [6]; the incidence of these complications is 45-80% [7].
Based on single open-door miniature titanium plate internal xation, we have developed a new type of spinal canal enlargement that lifts the lamina and preserves the posterior cervical ligament complex. It maintains the stability of the cervical spine, effectively leading to a reduced incidence of axial symptoms. The present study reviewed the imaging data of two groups of patients with multisegment cervical spondylotic myelopathy treated with either the new full lamina back shift spinal canal enlargement technique or single open-door miniature titanium plate internal xation. The cross-sectional area and the median sagittal diameter of the spinal canal and the distance of the spinal cord drift were measured and compared to evaluate the feasibility and advantages of the new type of spinal canal enlargement.

General data and grouping
The current clinical research protocol ful lled the requirements of the Helsinki Declaration and was approved by the Ethics Review Committee of the Second Hospital of Shanxi Medical University (2018LL039). All participants provided signed informed consent prior to registration.
A total of 32 patients with multisegment cervical spondylotic myelopathy underwent a new full lamina back shift spinal canal enlargement technique in our hospital between February 2017 and September 2018 and comprised the observation group (28 males and 4 females); the mean age was 57.3±1.7 (range, 49-76) years. Another group of 32 patients treated with single open-door miniature titanium plate internal xation comprised the control group (26 males and 6 females); the mean age was 56.8±1.6 (range, 46-77) years. No signi cant difference was detected in the baseline data between the two groups. Subsequently, preoperative and postoperative cervical X-ray, cervical CT, and cervical MRI were performed.
Inclusion criteria: Clinical symptoms and imaging examination leading to a diagnosis of cervical spondylotic myelopathy caused by cervical segmental disc herniation (≥3 segments) or cervical stenosis due to continuous posterior longitudinal ligament ossi cation; complete and clear preoperative and postoperative imaging data (X-ray, CT, MRI); complete followup data for >3 months; and completion of the clinical research protocol after provision of consent by the patients.
Exclusion criteria: refusal of the treatment plan; cervical vertebrae infection, fracture, tumor, and dysplasia; a combination of basic diseases such as severe diabetes and high blood pressure and an inability to undergo surgery; and incomplete clinical data.

Surgery
The operations for the two groups were performed by the same doctors. The patients were administered general anesthesia and placed in a prone position. The head and neck were slightly exed and xed by a stent. The skin and subcutaneous tissue were cut layer-by-layer until the spinous processes of the C2-T1 vertebrae were exposed.
Surgical procedure for the observation group: The bilateral paravertebral muscles were removed under the periosteum on both sides of the spinous process, exposing the C3-7 bilateral lamina and articular processes. Throughout the procedure, the C3-7 spinous processes, superior ligaments, and interspinous ligaments were preserved. Meanwhile, their connections with the posterior cervical muscle ligament complexes of C2 and T1 were not cut off. Holes were drilled in the bilateral laminae of the C3-7 segments, and screws were preplaced into the holes. The C3-7 bilateral inner and outer bone cortexes of the laminae were gradually removed at the junction of the articular process and lamina. Suitably sized self-developed microsupport titanium plates were selected and xed to both sides of the C3-7 vertebrae to achieve full lamina back shift expansion (Figures 1, 2, and 3). During the operation, the posterior dura mater of the C3-7 was not compressed, and the spinal cord was adequately decompressed. Then, an indwelling drainage catheter was implanted, and the surgical incision was closed layer-by-layer to complete the operation (Figures 3, 4, and 5).
Surgical procedure for the control group: The bilateral paravertebral muscles were removed under the periosteum on both sides of the spinous process, exposing the C3-7 bilateral lamina and articular processes. At the junction of the lamina and facet joint, a high-speed drill was used to make a groove in the bilateral lamina. The left side retained the inner panel as the hinge, while further drilling was performed on the right side to create the door in C3-7. During the operation, the cervical spinal cord achieved su cient bulging, and a preformed steel plate was placed on the open side of C3-7. An indwelling drainage catheter was implanted, and the incision was sutured layer-by-layer to complete the operation.

b. Median sagittal diameter
The median sagittal diameter of the C3-7 segments was measured on the sagittal images. The distance was estimated from the midpoint of the posterior margin of the vertebral body to the midpoint of the lamina (except for the pathological placeholders such as prominent discs and bone hyperplasias). The preoperative median sagittal diameter was de ned as d 1 , and the postoperative diameter was de ned as d 2 ; thus, the enlarged distance was calculated as d 2 -d 1 .

Spinal cord drift distance
The preoperative and immediate postoperative central sagittal cervical MRI T2-weighted images were used to measure the distance from the midpoint of the posterior border of the C3-7 segments to the center of the spinal cord with Photoshop CS5 software. The preoperative distance was b 1 , and the postoperative distance was b 2 ; thus, the spinal cord drift was calculated as b 2 -b 1 .

Statistical data processing
Statistical analysis of the measurement data was performed using SPSS21.0 software and is represented by the mean and standard deviation (±). The preoperative and postoperative parameters in one group and the parameters of the patients in the observation and control groups were compared by completely randomized independent samples t-tests at the α=0.05 level.

Results
A signi cant difference was detected between the preoperative and postoperative cross-sectional area of the spinal canal for each group (P < 0.05 for both). The enlarged cross-sectional area in each segment after surgery of the observation group was signi cantly better than that of the control group (P < 0.05 for all) (   Immediately after surgery, the T2-weighted MR images of both groups showed continuous recovery of the cerebrospinal uid signal for the C3-7 segments. No signi cant difference was detected in the overall and per-segment postoperative spinal cord drift distance between the two groups (P > 0.05) ( Table 3).   [15]. The incidence after single-door laminoplasty is 5.1% [16]. A majority of investigators have speculated that [17] C5 nerve root palsy is related to nerve root traction caused by excessive spinal cord drift after decompression. Moreover, the C5 level is located at the apex of the decompression, and the majority of the postoperative spinal cord drift occurs at this segment. Simultaneously, the C5 nerve root is short and projects from the spinal cord at an obtuse angle, causing it to be maximally damaged after compression. Imagama et al. [18]  Kawaguchi et al. [21] de ned long-term postoperative neck and shoulder pain accompanied by soreness and heavy feelings as axial symptoms. Yoshida et al. [22] suggested that the incidence of axial symptoms was reduced by preserving the posterior cervical spinous process ligament complex. Okada et al. conducted a prospective study [23] that showed a decrease in the incidence of axial symptoms after the surgery mentioned above. Different from the study of Steven Casha [24], the lamina and spinous processes of the decompression segment were completely separated from the other tissues, removed from the body, soaked in hydrogen peroxide, and reimplanted in the corresponding position for xation. For the new surgical procedure, we preserved the spinous processes, supraspinous ligaments and interspinous ligaments without removing the connection between the decompression segments and the upper and lower segments, maintaining their midline positions. Additionally, we sutured the muscles and ligaments in situ to maintain the integrity of the posterior cervical muscle and ligament complex to reduce the occurrence of axial symptoms. Consecutively, we used a selfdeveloped laminoplasty titanium plate to rigidly x the raised lamina bilaterally, which signi cantly enhanced the stability of the cervical spine surgery. Therefore, paravertebral muscle exercises could be performed sooner after surgery, reducing the possibility of axial symptoms. These results were in agreement with the study by Ito et al. [25].

Conclusions
In summary, the new full lamina back shift spinal canal enlargement technique achieved a thorough spinal canal decompression effect, thereby reducing the occurrence of axial symptoms and controlling the incidence of C5 nerve root palsy. We concluded that the clinical e cacy was satisfactory. Nevertheless, the correlations between different-sized titanium plates and the expansions of both the cross-sectional area of the spinal canal and the median sagittal diameter will be investigated in the future to further guide the use of this new technique in clinical practice.