In this study, 95% of the patients had excellent or good clinical efficacy, and the JOA, VAS, and NDI scores at the last follow-up were all significantly improved compared with those recorded preoperatively. No cervical MR images revealed cervical spinal cord compression or cerebrospinal fluid obstruction. No loosening, withdrawal, or fractures were observed at the site of the internal fixation. In this study, patients with cervical kyphosis had significantly improved cervical spine curvature at the last follow-up than at baseline, indicating that laminectomy with lateral mass screw internal fixation with or without laminoplasty can significantly improve cervical kyphosis. In contrast, patients with cervical lordosis did not have significantly different cervical spine curvature at the last follow-up compared with that at baseline, indicating that laminectomy with lateral mass screw internal fixation with or without laminoplasty is able to maintain the physiological curvature of the cervical spine (Fig. 1).
Laminoplasty and laminectomy with lateral mass screw internal fixation are two surgical options that use a posterior approach to treat CSM. Each surgery has different indications: laminoplasty is indicated for patients with developmental cervical spinal stenosis, cervical disc herniation, and more than three segments of ossification of the posterior longitudinal ligament; laminectomy with lateral mass screw internal fixation is indicated for patients with CSM and long-segment compression, severe compression, cervical instability, or cervical deformity. Laminectomy with lateral mass screw internal fixation has a higher incidence of C5 nerve palsy than laminoplasty, as an excessive backward drift of the cervical spinal cord is not prevented. While axial pain is more common in patients who undergo laminoplasty due to the stability of laminectomy with lateral mass screw internal fixation, laminoplasty results in a greater range of motion of the cervical spine. Previous studies observed no significant difference in the effectiveness of the recovery of neurological function between the two surgical methods [4, 5]; however, recurrent nerve compression injuries are more common after laminoplasty, as this surgical method results in a less stable cervical spine [6].
Laminectomy with lateral mass screw internal fixation has replaced the previous simple posterior cervical laminectomy procedure and is widely used to treat multi-segment CSM or posterior longitudinal ligament ossification. A simple laminectomy leads to a significant increase in the incidence of postoperative kyphosis. Laminectomy with lateral mass screw internal fixation stabilises the cervical spine to prevent complications, including cervical kyphosis [7]. The latter also provides good stability of the cervical spine to prevent the progression or recurrence of lesions at the surgical segment and allows surgeons to correct mild, rigid cervical kyphosis to restore the physiological curvature of the cervical spine. The operation is relatively safe, and intervertebral disc-osteophyte complexes can be reduced postoperatively to reduce anterior compression [8]. Compared with laminoplasty, laminectomy with lateral mass screw internal fixation delays the progression of ossification of the posterior longitudinal ligament (OPLL) [9].However, laminectomy with lateral mass screw internal fixation can lead to posterior cervical axial symptoms, which are mainly caused by the imbalance of the muscles of the posterior neck, adhesions, scar compression, and excessive cervical spinal cord drift. This procedure may also result in C5 nerve palsy (excessive traction caused by drift of the dural sac and cervical spinal cord, especially in the presence of nerve root canal stenosis), cervical spinal cord drift, and unstable activity. Delayed and excessive cervical spinal cord drift can lead to injuries, especially in patients with existing cervical spinal cord disease [10].
The risk of C5 nerve palsy after laminectomy with lateral mass screw internal fixation can be reduced by using a precise surgical protocol, including precise laminectomy widths (not to exceed the width of the spinal cord by >2–3 mm or the width of the dural sac) to limit the drift of the dural sac [11].Identifying risk factors to predict complications is also necessary. C5 nerve traction paralysis has been associated with the presence of C4–5 intervertebral foraminal stenosis, and preventive decompression of the intervertebral foraminal area can help expand the nerve root canal space [12].
Improvements to the surgical methods of laminectomy with lateral mass screw internal fixation can help reduce the complication rate. Therefore, we combined laminectomy with lateral mass screw internal fixation with laminoplasty of 1–2 spinal segments to prevent excessive cervical spinal cord drift. A previous study reported that laminectomy and internal fixation were performed at the same time as selective blocking, single-doorlaminoplastiesin1–2 spinal segments [13].The spinous processes were suspended with the lateral mass screw with a thread in this previous study. Our results indicate that the selective blocking of laminoplasty combined with laminectomy with lateral mass screw internal fixation can prevent excessive backward drift of the cervical spinal cord, thereby significantly reducing the incidence of postoperative C5 paralysis and cervical spinal cord injuries. Inpatients with severe anterior and posterior compression and an anterior occupancy≤60%, the volume of the corresponding segment of the spinal canal can be controlled by adjusting the width of the blocking plate to open the door, thereby preventing excessive posterior drift of the cervical spinal cord. None of the 12 patients who underwent laminectomy and lateral mass screw fixation combined with 1–2 level laminoplasty developed C5 palsy(Fig. 2).
The surgical method used to treat severe and complex CSM is important. In routine cases, the operative method is selected according to the operative indications. Laminectomy with lateral mass screw fixation is the first choice for patients with severe symptoms or injuries to the cervical spinal cord or canal space. Decompression results in a significantly increased spinal canal space and good cervical spine stability, and the procedure is relatively safe. After laminectomy with lateral mass screw internal fixation, the compression in patients with severe anterior and posterior compression cannot change, as the cervical spine has been stabilised. Therefore, anterior surgery is not required. No patients in this study required anterior surgery.
Laminectomy with lateral mass screw internal fixation can also correct mild kyphosis with some mobility (kyphosis angle <20°). The K-line, the straight line connecting the midpoint of the spinal canal from C2 to C7, is often utilised in clinical practice and can be used as a reference index for the indication of posterior cervical surgery. When the OPLL range does not exceed the K-line on a standard lateral radiograph, the K-line is positive, and posterior decompression surgery is indicated. When the OPLL range exceeds the K-line on a standard lateral radiograph, the K-line is negative, indicating insufficient spinal cord drift. When the spinal canal invasion rate is≥60%, anterior surgery is indicated. However, when the K-line is positive and the spinal canal invasion rate is≥60%, posterior decompression is not contraindicated [14].Two main factors affect the K-line: cervical spine curvature and spinal canal pressure. Changes in these factors affect the selection of surgical method. We believe that the curvature of the cervical spine can be changed to affect the K-line to indicate posterior surgery, which is safer and more effective than anterior surgery. When the cervical kyphosis is >10°–13°, it affects the drift of the cervical spinal cord, and posterior surgery is not indicated. The cervical spine is generally unstable in these patients, and the kyphotic deformity of the cervical spine can be corrected through fixation with side mass screws (Fig. 3).
This study has notable limitations. First, the sample size of the follow-up cases was small. Second, the follow-up time was insufficient. Further follow-up is needed to verify procedural efficacy.