Posterior Laminectomy and Lateral Mass Screw Fixation for the Treatment of Severe Cervical Spondylotic Myelopathy

Severe and complex cervical spondylotic myelopathy(CSM) requires surgical treatment. The common methods of posterior cervical spine surgery are laminoplasty and laminectomy with lateral mass screw internal xation. However, the operative effect of this surgical approach is unclear owing to the complexity and severity of CSM in patients who undergo this surgical treatment.Therefore, we aimed to evaluate the clinical effects of posterior cervical laminectomy and lateral mass screw internal xation in patients with severe and complex CSM. signicant muscle strength; severe the cervical spinal canal on obvious ischaemic changes in the cervical spinal cord; posterior longitudinal ligament with severe anterior and posterior compression; and contraindications for anterior or posterior laminoplasty.


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Background Severe and complex cervical spondylotic myelopathy(CSM) requires surgical treatment. The most common surgical approaches include the anterior, posterior, and combined anterior and posterior approaches. A speci c surgical approach is chosen according to the patient's condition. An anterior approach to the cervical spine is widely used to remove anterior compressive material; however, it does not provide su cient decompression for CSM with severe compression of the anterior and posterior long segments [1].Some patients with CSM have cervical spinal deformities or instability, requiring posterior surgery.
The common methods of posterior cervical spine surgery are laminoplasty and laminectomy with lateral mass screw internal xation. The latter is a safer and more adequate treatment option for patients with severe, indirect, multilevel cervical cord compression. It allows for removal of the lamina and ligamentum avum, and cervical spinal canal enlargement. The dural sac and cervical spinal cord are able to drift backward, relieving or eliminating the compression from the anterior and posterior sides of the spinal cord and achieving direct and indirect decompression [2].This procedure is used to treat CSM caused by severe complex degeneration, posterior longitudinal ligament ossi cation, ligamentum avum thickening, or congenital stenosis of the cervical spinal canal. The operative effect of posterior laminectomy and lateral mass screw xation is unclear owing to the complexity and severity of the disease in patients who undergo this surgical treatment [3].
Thus, this study aimed to evaluate the clinical effects of this surgical procedure in 60 patients with severe and complex CSM.We hypothesised that posterior laminectomy and lateral mass screw xation (PLF) would result in favourable clinical outcomes.

Patients and study design
Data for patients with complex and severe CSM who underwent posterior cervical laminectomy and lateral mass screw internal xation from May 2013 to June 2020 at our hospital were retrospectively reviewed.The Ethics Committee of our institution approved this study, and informed consent was obtained from the patients.
The inclusion criteria were as follows:multilevel CSM (no less than three levels) combined with instability (sigmatic vertebral translation in hyper exion and hyperextension surgery segment>3mm or angle>11°) or deformity (kyphosis angle<20°,with mild lateral or anteroposterior displacement); severe medullary symptoms and signs, including Hoffman's sign and ankle clonus, increased muscle tone, and signi cant decrease in muscle strength; severe stenosis of the cervical spinal canal suggested on imaging with obvious ischaemic changes in the cervical spinal cord; posterior longitudinal ligament ossi cation with severe anterior and posterior compression; and contraindications for anterior or posterior laminoplasty.
Patients with severe anterior and posterior cervical compression with≥60% anterior compression requiring anterior and posterior surgeries were excluded from the study.
The patients were routinely examined using cervical spine lateral and hyperextension radiographs, threedimensional computed tomography (CT), and cervical magnetic resonance imaging (MRI). The postoperative follow-up period ranged from 6 months to 6 years (mean 3.6 years).

Surgical methods
Laminectomy and lateral mass screw internal xation were performed with the patient in the prone position under general anaesthesia. First, a posterior medial incision of the cervical spine was made. The fascia and paravertebral muscles were removed from the spinous process bilaterally to fully expose the lateral mass surface. Lateral mass nails were implanted in C3-7 bilaterally. A grinding drill was used to create a 3-mm wide slot in the inner lamina of the facet joint to reach the inner cortex, and a 1-2-mm thick lamina rongeur was used to bite the inner cortex to complete the slot. Kocher forceps were used to clamp the spinous process and carefully lift the entire lamina from the spinal canal. The lamina was moved to either side, and lamina forceps were used to bite the ligamentum avum to ensure complete separation from the dural sac. Complete removal of the lamina exposed the sides of the dural sac and entire surface of the facet joints.If the patient had nerve root-type symptoms, foraminal incision decompression was performed. The connecting rod and horizontal connections were installed.C-arm uoroscopy was used to con rm the ideal position of the internal xation. Bone granules were implanted bilaterally on the surfaces of the spine to promote bone fusion.All operations were performed by the same surgeon.

Modi ed surgery
Laminectomy and lateral mass screw internal xation were combined with 1-2 level laminoplasty to prevent excessive cervical spine drift. The C5 and upper or lower segment were used for the laminoplasty. If the patient had severe neurological symptoms, laminoplasty was approached on the symptomatic side.
A drill was used to grind the outer cortex and create a groove at the transition of the lamina and lateral mass. After thinning, the rongeur was used to bite the inner cortex and simultaneously open a door. The lateral ligamentum avum was completely loosened and separated. A grinding drill was used on the side of the portal axis to grind off the outer cortex at the junction of the lamina and the lateral mass to form a hinge. The lamina was gently opened at the door until the laminectomy was completed, and the width of the door was12-14mm.A curved-arch titanium plate (Synthes, GmbH,Switzerland) was xed to both ends of the door. Bone granules were implanted in the hinge area to promote bone fusion and form a permanent spinal canal.All operations were performed by the same surgeon.

Postoperative treatment
Antibiotics, mannitol, dexamethasone, nebulised inhalation medications, and other symptomatic therapies were administered to the patients for the rst 3-5 days postoperatively. The drainage tube was removed on postoperative day 3-5, and patients were encouraged to ambulate by postoperative day 3-5.
Patients wore an immobilising cervical brace for 6 weeks. Cervical spine radiographs and MR images were obtained6 weeks postoperatively.

Imaging evaluations
Cobb's angle was measured on lateral radiographs of the cervical spine. A positive value indicated lordosis, and a negative value indicated kyphosis. The preoperative and postoperative angles were compared.

Cervical MRI
Cervical MR images were used to detect the degree of backward drift of the cervical spinal cord, recompression, and obstruction of the cerebrospinal uid.

Evaluation of clinical e cacy
The Japanese Orthopaedic Association (JOA)scores at baseline and nal follow-up were compared to evaluate the improvement in neurological symptoms, the visual analogue scale (VAS) was used to evaluate pain severity, and the cervical neck disability index (NDI) was used to assess the degree of cervical dysfunction.Odom's classi cation was used to evaluate the comprehensive clinical e cacy at the last follow-up. The clinical e cacy was classi ed as follows:excellent in patients whose preoperative symptoms disappeared completely and whose daily lives were no longer affected by their condition, good in patients whose preoperative symptoms were signi cantly relieved with no obvious limitations in daily life, general in patients whose preoperative symptoms were partially relieved and whose daily lives were partially limited, and poor in patients whose preoperative symptoms did not improve or worsened.

Postoperative complications
The following postoperative complications were evaluated: fusion of the surgical segments, restenosis, loosened or broken internal xations, cerebrospinal uid leakage, incision infection, allergic reactions to implant materials, and vascular, nerve, or spinal injuries.

Statistical methods
All analyses were performed with SPSS version 20.0 statistical software (IBM Inc., Chicago, IL, USA).
Statistical signi cance was set at P<0.05. Data are expressed as mean ± standard deviation. The baseline and nal cervical physiological curvatures, JOA scores, VAS scores, and NDI scores were compared using the intra-group t-test.

Results
In the 60patients included in this study (Table 1), there were no reports of vascular, nerve, or spinal injuries, cerebrospinal uid leakage, infection, allergies to implant materials, restenosis, loosening or breakage of the internal xation, compression of the spinal cord, or obstructed cerebrospinal uid.  Two patients experienced mild posterior cervical axial pain that resolved over the course of 3 months. Unilateral C5 nerve palsy occurred in three patients and resolved after a few weeks. Two patients with limb muscle weakness required medication and rehabilitation. One patient experienced limb muscle loss due to a fall, which occurred 1monthpostoperatively and recovered after several months. None of the 12patients who underwent laminectomy and lateral mass screw xation combined with 1-2 level laminoplasty developed C5 palsy.

Discussion
In this study, 95% of the patients had excellent or good clinical e cacy, and the JOA, VAS, and NDI scores at the last follow-up were all signi cantly improved compared with those recorded preoperatively. No cervical MR images revealed cervical spinal cord compression or cerebrospinal uid obstruction. No loosening, withdrawal, or fractures were observed at the site of the internal xation. In this study, patients with cervical kyphosis had signi cantly improved cervical spine curvature at the last follow-up than at baseline, indicating that laminectomy with lateral mass screw internal xation with or without laminoplasty can signi cantly improve cervical kyphosis. In contrast, patients with cervical lordosis did not have signi cantly different cervical spine curvature at the last follow-up compared with that at baseline, indicating that laminectomy with lateral mass screw internal xation 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 xation 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 ossi cation of the posterior longitudinal ligament; laminectomy with lateral mass screw internal xation is indicated for patients with CSM and long-segment compression, severe compression, cervical instability, or cervical deformity. Laminectomy with lateral mass screw internal xation 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 xation, laminoplasty results in a greater range of motion of the cervical spine. Previous studies observed no signi cant 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 xation has replaced the previous simple posterior cervical laminectomy procedure and is widely used to treat multi-segment CSM or posterior longitudinal ligament ossi cation. A simple laminectomy leads to a signi cant increase in the incidence of postoperative kyphosis. Laminectomy with lateral mass screw internal xation 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 xation delays the progression of ossi cation of the posterior longitudinal ligament (OPLL) [9].However, laminectomy with lateral mass screw internal xation 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 xation 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 xation can help reduce the complication rate. Therefore, we combined laminectomy with lateral mass screw internal xation with laminoplasty of 1-2 spinal segments to prevent excessive cervical spinal cord drift. A previous study reported that laminectomy and internal xation 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 xation can prevent excessive backward drift of the cervical spinal cord, thereby signi cantly 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 xation 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 xation is the rst choice for patients with severe symptoms or injuries to the cervical spinal cord or canal space. Decompression results in a signi cantly increased spinal canal space and good cervical spine stability, and the procedure is relatively safe. After laminectomy with lateral mass screw internal xation, 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 xation 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 Kline is positive, and posterior decompression surgery is indicated. When the OPLL range exceeds the Kline on a standard lateral radiograph, the K-line is negative, indicating insu cient 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 xation 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 insu cient. Further follow-up is needed to verify procedural e cacy.

Conclusions
In conclusion, several surgical methods can be used to treat CSM. Posterior cervical laminectomy combined with lateral mass screw xation has excellent clinical e cacy. Combining this surgical method with laminoplasty of 1-2 spinal segments stabilises the cervical spine and spinal decompression while preventing excessive backward drift of the cervical spinal cord, resulting in fewer complications.

Declarations
We declare that experimental research on humans or the use of human tissues comply with international guidelines. We con rm that all methods were carried out in accordance with relevant guidelines and regulations.
Ethics approval and Consent to Participate: The Ethics Committee of of Union Hospital, Tongji Medical College, Huazhong University of Science and Technology approved this study. Informed consent was obtained from the patients. Consent for publication: Written informed consent for publication was obtained from all participants.
Availability of data and materials: The data sets supporting the results of this article are included within the article and its additional les.
Competing Interests: The authors declare that they have no competing interests. I declare that the authors have no competing interests as de ned by BMC, or other interests that might be perceived to in uence the results and/or discussion reported in this paper.
Funding: Not applicable   Laminectomy and lateral mass screw internal xation were combined with 1-2 level laminoplasty A 36-year-old man with cervical spondylotic myelopathy with incomplete paralysis, ossi cation of the posterior longitudinal ligament of the cervical spine, and cervical kyphosis underwent C3-7 lateral mass screw internal xation and fusion; C3, C4, and C5 total laminectomy; and C6-7laminoplasty.