1.1 Patient Case Selection and General Information
We obtained ethical approval exemption from our ethics committee to perform this study since we didn’t have direct contact with the participants. Patients treated for CSR in database records of our hospital were retrospectively analyzed from Dec 1, 2016, to Apr 30, 2020.
Inclusion criteria were as follows: 1) patients with single nerve root symptoms, and their cervical imaging data (including anteroposterior and lateral radiograph, hyperflexion and hyperextension radiograph, three-dimensional reconstruction CT and MRI) showed single-level and unilateral foraminal bony stenosis with bony herniation, 2) the nerve root symptoms were consistent with the focus location of the imaging data, 3) If necessary, angiography and block would be performed to identify the responsible nerve root, and 4) the conservative treatment failed to produce the desired results or the symptoms got progressively worse after 6 weeks, which seriously affected daily life and work. Exclusion criteria including: 1) patients with cervical segmental instability or nerve root disease, 2) patients with neck skin infection and history of posterior cervical surgery, 3) patients with central stenosis, spinal cord compression or symptoms of multi-level nerve root injury, 4) patients with severe systemic disease or organ dysfunction that cannot tolerate surgery.
1.2 Surgical Procedure and Postoperative Management
The posture refers to professor Rutten's method [6]. The patient's head is connected to the Mayfield head rest and fixed in hyperflexion position to open the posterior intervertebral space. Both lower extremities are in hip and knee flexion, and padded for protection.
The focus is located by anteroposterior and lateral radiograph. An 8mm incision is made after local anesthesia. Place in and position the primary dilator accurately, then screw in the working sleeve. Subsequently, insert the endoscope. After connecting the lavage device, use nucleus pulposus forceps and a high-radiofrequency electrotome to clean the muscle and soft tissue on the surface of lamina. Once the "V" point is clearly identified, use a high-speed drill to expand the lamina space from head to tail. Generally, grind off the lower edge of upper lamina and the upper edge of lower lamina by about 3mm respectively. Grind off the inner edge of lateral mass by 3mm to the outside simultaneously. Remove the ligamentum flavum with basket forceps and gun forceps. Use the nerve hook to separate the scar on nerve and identify the spinal cord and exiting root. Next, grind off the upper edge of the lower cervical pedicle to create a potential channel from the axilla of nerve root to the rear of the intervertebral space. Gently rotate the working sleeve to protect the spinal cord and nerve root, adjust the lens to aim at the intervertebral space, excise the herniated nucleus pulposus and annulus fibrosus with nucleus pulposus forceps, and cut off the posterior osteophyte of the intervertebral space with an osteotome or a drill. Then explore again whether there is residual nucleus pulposus or osteophyte around the nerve root, perform annulus fibroplasty with the radiofrequency electrotome, and inject dexamethasone after hemostasis. Finally, remove the working sleeve followed by wound closure (Figure 1).
Routine swelling and pain relief and neurotrophic treatment are performed after the operation. Patients can begin out-of-bed activities with soft neck braces on the 2nd postoperative day. The neck brace should be worn for 4 weeks. The postoperative outpatient and telephone follow-up last for 6-18 months, with an average of 11.2 ± 6.5 months.
1.3 Effectiveness Evaluation
Operation time and length of stay were recorded. Relevant surgical complications such as infection, spinal cord and nerve injury, and systemic manifestations were also collected. The pain was evaluated based on visual analog scale (VAS). In addition, Japanese Orthopaedic Association (JOA) scores was used to assess the improvement in the motor, sensory and bladder dysfunction of patients. VAS and JOA score were recorded routinely on admission, at postoperative 1 week and 3 months, and at the last follow-up.
1.4 Imaging Evaluation
The intervertebral foramen height and anteroposterior diameter, and intervertebral foramen area were measured pre- and postoperatively (1 week). The sagittal section of the internal edge of the pedicle on operated side was defined as the measuring plane, and the height and diameter were measured based on this plane. For intervertebral foramen area, we transferring the thin-layer scanning DICOM data to the workstation (syngo.via, software version:VB40, Siemens Healthineers, Forchhiem, Germany), performing multiplanar reconstruction (MPR) in the vertical direction of the intervertebral foramen, manually found and determined the best display layer. Then we used the area measuring tool to sketch along the contour curve of the intervertebral foramen, and obtained the contour area (cm2) after drawing. Finally, we recorded the results.
In addition, cervical radiographs in hyperflexion and hyperextension position were collected before and 3 months after the operation. The evaluation standard of cervical instability (angular displacement larger than 10° or horizontal displacement larger than 3.0 mm) was used to judge whether there was postoperative segmental instability [7].
1.5 Statistical Analysis
Statistical Packages of Social Sciences (SPSS) software (version 22.0) was used to analyze the collected data. The measurement data were expressed by means and standard deviations (x̄ ± s). Differences in variables before and after the operation were analyzed through one-way ANOVA or paired t-test. Meanwhile, p<0.05 was considered statistically significant.