Participants in the present study comprised Sixty-eight patients who underwent LP as decompression surgery for CSM were involved in the present study. Exclusion criteria were myelopathy caused by single-level disc herniation, OPLL, or a history of cervical spinal surgery, spinal tumor, trauma, and infection.
As the ethics approval, the study protocol was approved by the Institutional Review Board of Kindai University Hospital ( Control Cohort Study, No.2020-025). We conducted this study under approval of the institutional review board and informed consent was obtained from all patients.
The operative technique was previously described by Miyazaki and Kirita’s method (n = 64) and a modification of Kurokawa’s method (n = 4). The method of Miyazaki and Kirita was a procedure in which bilateral gutters were made and the laminae were split in the middle with a high-speed drill. The laminae were kept open with nylon sutures in the deep fascia bilaterally. The modification of Kurokawa’s method was the procedure in which mid-splitting of the spinous processes was performed using a T-saw [10]. After spreading the split spinous processes, hydroxyappatite spacers were sutured as necessary between the opened spinous process at each level.
We were able to obtain follow-up results for all 68 patients (50 males and 18 females). Mean age at surgery was 60.3 years (range, 32–92 years). All patients were followed-up for 2 year or longer after surgery. Mean follow-up period was 74.2 months (Table 1). The spinal levels of decompression were from C3 to C7 in 47 patients, C4 to C7 in 4 patients, C3 to C6 in 8 patients, C3 to Th1 and C2 to C7 in 3 patients each, and C4 to C5, C3 to C5 and C4 to Th1 in 1 patient each.
Table 1
Background characteristics of the participants
Characteristic | |
Age (years old) | 60.3 ± 12.4 |
Sex (male/female) | 50 / 18 |
Follow-up period (months) | 74 ± 43.5 |
The JOA score at preoperation (points) | 9.7 ± 2.9 |
The JOA score at follow-up (points) | 13.0 ± 2.6 |
The RR (%) of the JOA score | 45.5 ± 28.0 |
C2-7 angle at preoperation (degrees) | 4.1 ± 12.5 |
C2-7 angle at follow-up (degrees) | 6.6 ± 14.3 |
Data are presented as means ± SD. |
JOA: Japanese Orthopaedic Association |
RR: recovery rate |
Clinical Findings
The Japanese Orthopaedic Association (JOA) scoring system was used to evaluate the severity of cervical myelopathy preoperativly and at the final follow-up. The recovery rate (RR) of the JOA score was calculated using the method of Hirabayashi et al. to compare preoperatively and at final follow-up JOA scores. As defined by Hirabayashi et al., RR (%) was calculated as (postoperative JOA score – preoperative JOA score) / (17- preoperative JOA score) × 100.
Radiological Evaluation
C2-7 angle was measured on T2-weighted sagittal images of magnetic resonance imaging (MRI) preoperatively and at the final follow-up. In CSM patients, although C2-7 angle was positive, local kyphosis existed due to the alignment (e.g., sigmoid, reverse sigmoid, and kyphosis) in several patients. In those cases, local kyphosis angle was also measured on T2-weighted sagittal images of MRI at preoperatively and at the follow-up. The K-line was defined as the straight line connecting the midpoints of the spinal canal at C2 and C7 on midsagittal T2-weighted MRI in the present study. The patients were divided into two groups; K-line (-) and K-line (+). In the K-line (-) group, the anterior structural factors (e.,g., disc herniation, osteophyte, or kyphotic beak of the vertebra) crossed the K-line with no space between the K-line and the anterior wall of the canal. On the other hand, in the K-line (+) group, the anterior structural factors did not exceed K-line and stayed within the ventral area of K-line.
Clinical parameters such as gender, age, preoperative JOA score, the JOA score at the follow-up, the RR of the JOA score, and radiological parameters such as preoperative C2-7 angle, C2-7 angle at the follow-up, preoperative local kyphosis angle, and the local kyphosis angle at the follow-up were compared between K-line(-) and K-line (+).
Statistical analysis was performed using Student t-test and Mann-Whitney U test, with P < 0.05 considered statistically significant. Statistical analyses of data were performed with Stat Flex Ver.6 (Artech Co., Ltd., Osaka, Japan). Results were presented as means ± SD.