Patients and study design
Data for patients with complex and severe CSM who underwent posterior cervical laminectomy and lateral mass screw internal fixation between May 2013 and 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: multi-level CSM (no less than three levels) combined with instability (sigmatic vertebral translation in hyperflexion 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 significant decrease in muscle strength; severe stenosis of the cervical spinal canal suggested on imaging with obvious ischaemic changes in the cervical spinal cord; CSM with discontinuous ossification of the posterior longitudinal ligament and 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.
Patients were routinely examined using cervical spine lateral and hyperextension radiography, three-dimensional computed tomography, and cervical magnetic resonance(MR)imaging. The post-operative follow-up period ranged from 1 to 6 years (mean 3.6 years).
Surgical methods
Laminectomy and lateral mass screw internal fixation 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 ligamentumflavum to ensure complete separation from the dural sac. Complete removal of the lamina exposed the sides of the dural sac and the entire surface of the facet joints. If the patient had nerve root-type symptoms, foraminal incision decompression was performed. To maintain cervical lordosis or correct cervical kyphosis, proper compression screws were applied and nuts and connecting rods were installed.C-arm fluoroscopy was used to confirm the ideal position of the internal fixation. Bone granules were implanted on both sides of the lateral mass to promote osseous fusion. All operations were performed by the same surgeon.
Modified surgery
Laminectomy and lateral mass screw internal fixation 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 createa ‘door’ 12–14mm wide. The lateral ligamentumflavum 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.A curved-arch titanium plate (Synthes GmbH, Zuchwil, Switzerland) was fixed 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.
Post-operative treatment
Antibiotics, mannitol, dexamethasone, nebulised inhalation medications, and other symptomatic therapies were administered to the patients for the first 3–5 days post-operatively. The drainage tube was removed on post-operative day 3–5, and patients were encouraged to ambulate by post-operative day 3–5. Patients wore an immobilising cervical brace for 12 weeks. Cervical spine radiographs and MR images were obtained 1 week post-operatively.
Effect analysis
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 pre- and post-operative angles were compared.
Cervical MR imaging
Cervical MR images were used to detect the degree of backward drift of the cervical spinal cord, re-compression, and obstruction of the cerebrospinal fluid.
Evaluation of clinical efficacy
The Japanese Orthopaedic Association (JOA)scores at baseline and final 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 classification was used to evaluate the comprehensive clinical efficacy at the last follow-up. The clinical efficacy was classified as follows: excellent in patients whose pre-operative symptoms resolved completely and whose daily lives were no longer affected by their condition,good in patients whose pre-operative symptoms were significantly relieved with no obvious limitations in daily life, general in patients whose pre-operative symptoms were partially relieved and whose daily lives were partially limited, and poor in patients whose pre-operative symptoms did not improve or worsened.
Post-operative complications
The following post-operative complications were evaluated: fusion of the surgical segments, restenosis, loosened or broken internal fixations, cerebrospinal fluid 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 significance was set at P<0.05. Data are expressed as mean ± standard deviation. The baseline and final cervical physiological curvatures and JOA, VAS, and NDI scores were compared using intra-group t-tests.