General data and grouping
The current clinical research protocol fulfilled 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 fixation comprised the control group (26 males and 6 females); the mean age was 56.8±1.6 (range, 46–77) years. No significant 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: ① 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 ossification; ② complete and clear preoperative and postoperative imaging data (X-ray, CT, MRI); ③ complete follow-up data for >3 months; and ④ completion of the clinical research protocol after provision of consent by the patients.
Exclusion criteria: ① refusal of the treatment plan; ②cervical vertebrae infection, fracture, tumor, and dysplasia; ③ a combination of basic diseases such as severe diabetes and high blood pressure and an inability to undergo surgery; and ④incomplete clinical data.
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 flexed and fixed 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 fixed 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 sufficient 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.
Cross-sectional area and median sagittal diameter of the spinal canal
The cervical CT data (64-slice CT 0.625 mm thin-layer scan) of 62 patients were imported into Mimics 17.0 software in DICOM format for evaluation.
a. Cross-sectional area
The segmentation function in Mimics 17.0 software was used to select the measurement area. The ability to automatically identify the edge of the spinal canal  allowed measurement of the cross-sectional area of the spinal canal for the C3–7 segments at the midpoint plane of the pedicle. The posterior edge of the vertebral body or the posterior margin of the pathological placeholder, such as the intervertebral disc or the posterior longitudinal ligament ossification, was chosen as the anterior border of the spinal canal. The posterior border was defined as the anterior edge of the segmental lamina and both sides of the inner edge of the pedicle. The preoperative cross-sectional area was defined as S1, and the postoperative area was defined as S2. Thus, the enlarged area was calculated as S2-S1.
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 defined as d1, and the postoperative diameter was defined as d2; thus, the enlarged distance was calculated as d2-d1.
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 b1, and the postoperative distance was b2; thus, the spinal cord drift was calculated as b2-b1.
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.