Biomechanical Analysis And Clinical Research On Cervical Stability After Cervical Posterior Operations

Part1Biomechanical analysis on cervical stability after cervical posterior operationsObjective:Due to removing the posterior tension-band (including ligamentum nuchae, ligamenta interspinalia, ligamentum flavum and vertebral arch) by Open-door laminoplasty (LP) and laminectomy (LC), some surgery-related late complications are often observed in the long-term follow-up, including instability, progressive kyphosis neurological deterioration and axial symptoms, which seriously affect the neurological recovery and the life quality of the patients. Through the biomechanical experiments, this study aims to investigate the impacts on cervical stability after cervical different posterior multilevel decompression, providing a theoretical reference for clinical treatment.Methods:A total of16adult male goats C1～T1cervical specimens were randomly divided into four groups:Control group included4cases without any treatment, Laminoplasty (LP) group consisted of4cases, Laminectomy (LC) group included4cases, and Laminectomy with pedicle screw fixation (LPS) group consisted of4cases. After the preparation of specimens, we compressed and torsioned the specimens using Bose ElectroForce3520-AT biomechanical machine, and reported compression, torsion angles and stress. Differences of cervical stability among the four groups were compared using One-way ANOVA and Student-Newman-Keuls tests.Results:(1) Compression test results:the mechanical stress on C5vertebral was maximum in LC group, moderate in LP group, minimum in Control group and LPS group; the differences were statistically signicant among the Control group, LC group, LP group and LPS group (P<0.05).(2) Torsion test results:ANOVA test showed that there was significant differences in the cervical torsional stiffness under the different torsion angles among the four groups (P<0.001). SNK test shows that when the torsion angle is2°and4°, there was no statistical significance between LP and LC group (P>0.05), while there was statistical significance between LP, LPS and control group(P <0.001), and between LC, LPS and control group (P<0.001); the torsion stiffness was maximum in LPS group, moderate in Control group, minimum in LP and LC group. When torsion angle is6°,8°and10°, there was statistical significance among the four groups (P<0.001); the torsion stiffness was maximum in LPS group, moderate in Control group, followed by LP group and minimum in LC group.Conclusion:Laminectomy with pedicle screw fixation (LPS) removed the cervical posterior tension-band, but the pedicle screw fixation provided multilevel cervical posterior decompression with the immediate stability; Open-door laminoplasty partly reserved the cervical posterior tension-band, and also maintained the reliable stability for multilevel cervical posterior decompression. Laminectomy (LC) removed the cervical posterior tension-band, and resulted in a poor cervical stability.Part2Long-term impacts of different posterior operations on curvature, neurological recovery and axial symptoms for multilevel cervical degenerative myelopathyObjective:Multilevel cervical degenerative myelopathy (CDM) is usually treated by different posterior decompression techniques. Laminoplasty has been considered as an effective and safe method to widen the spinal canal dimensions without removing the dorsal elements of the cervical spine. Laminectomy allows adequate decompression of the spinal cord, and can be performed safely and easily. Hence, a satisfactory surgical outcome in a short time is often seen in patients undergoing laminectomy. However, some late operation-related complications have also been observed in laminoplasty and laminectomy, which include segmental instability, loss of cervical lordosis, neurological deterioration and axial symptoms. In recent years, laminectomy with lateral mass screw fixation, which can obtain adequate decompression of the spinal cord and immediate cervical stability, has been widely performed with favorable outcomes in the mid-term follow-up. At present, it remains controversial whether different posterior operations have long-term adverse impacts on cervical curvature, neurological improvement and axial symptoms for multilevel CDM. Moreover, there are few reports on the relationship among curvature changes, recovery rate and axial symptom severity. The purpose of this study was to investigate the long-term impacts of different posterior operations on curvature, neurological improvement and axial symptoms for multilevel cervical degenerative myelopathy (CDM), and to study the relationship among loss of cervical lordosis, recovery rate and axial symptom severity.Methods:We retrospectively reviewed98patients with multilevel CDM who had undergone laminoplasty (Group LP,36patients), laminectomy (Group LC,30patients), or laminectomy with lateral mass screw fixation (Group LCS,32patients) between January2000and January2005. Loss of curvature index (CI) was measured according to the preoperative and final follow-up radiographic parameters. The recovery rate was calculated based on the Japanese Orthopedic Association (JOA) score. Axial symptom severity was quantified by Neck Disability Index (NDI).Results:Analysis of final follow-up data showed significant differences among the3groups regarding loss of CI (F=41.46,P<0.001), between preoperative and final follow-up JOA scores (P<0.001), final follow-up JOA score (F=7.81, P<0.001), recovery rate (F=12.98, P<0.001) and axial symptom severity (χ2=18.04, P<0.001). Loss of CI showed negative association with neurological recovery (r=-0.555, P<0.001) and positive correlation with axial symptom severity(r=0.696,P<0.001).Conclusion:Excellent neurological improvement was obtained by LP and LCS for patients with multilevel CDM, while loss of CI in groups LP and LC caused a high incidence of axial symptoms. Loss of CI was correlated with poor neurological recovery and axial symptom severity. Lateral mass screw fixation can effectively prevent loss of postoperative cervical curvature and reduce incidence of axial symptoms.Part3Posterior selectively enlarged laminectomy and lateral mass screw fixation for multilevel cervical degenerative myelopathy associated with kyphosisObjective:Surgical management for patients with multilevel cervical myelopathy related to cervical kyphosis aims to decompress the spinal cord and restore the normal sagittal alignment using either an anterior or a posterior approach. However, multilevel anterior approach decompression has been associated with a high incidence of cord injury, cerebrospinal fluid leakage (CFL), graft failure and pseudarthrosis; multi-segmental posterior decompression might hinder neurological recovery because of the progression of kyphosis and segmental instability, as well from complications such as axial symptoms and C5root palsy. The optimal surgical strategy for the management of multilevel CDM with kyphotic deformity remains controversial, due to the shortcomings of each surgical approach. The purpose of this study was to investigate the surgical efficacy and complications prevention of posterior selevtively enlarged laminectomy (removing the inside edge of facet joints and decompressing the nerve foramina) and lateral mass screw fixation for the treatment of multilevel cervical degenerative myelopathy (CDM) associated with kyphosis.Methods:A total of43patients (28men and15women; average age59.6years) with multilevel CDM correlated to kyphosis were obtained in the study. All radiological data was record on computer based measurement from pre-or postoperative X-ray, MRI and CT. All neurological parameters were accessed in each patient. Analysis consisted of:Japanese Orthopedic Association (JOA) score, recovery rate, curvature index (CI), the expansion degree and the drift-back distance of the spinal cord, axial symptom severity and C5root palsy. The JOA scoring system and Neck Disability Index (NDI) scoring were applied to evaluate the neurological function and neck/shoulder axial pain before and after surgery respectively. Ishihara method was employed to measure cervical curvature index (CI). The degree of spinal cord expanding and shifting was calculated in MRI. Statistical analysis was performed using paired t test with significance set at P<0.05.Results:The43patients were performed the surgical decompression for mean3.91±0.86segments (ranged3～5segments) and followed up for average38months (ranged20～60months). There were significant differences between post-and pre-operative JOA score (14.31±1.33vs.8.16±1.11), CI (15.30%±3.18%vs.7.36%±9.69%), anteroposterior diameter at the level of maximum compression of the dural sac in MRI (6.10±0.89mm vs.2.92±1.49mm), NDI score (4.90±2.46vs.19.36±8.61), and the excellent and good rate was95.34%. The mean spinal cord posterior shift was4.59±1.20mm (ranged2.97～6.68mm). Bone graft was completely fused for3-6months after surgery. During the follow-up period, only2patients (4.7%) did not obtain complete recovery,4patients (9.3%) experienced axial symptoms. There were no C5root palsy or instrument failure occurred in all patients.Conclusion:The posterior selectively enlarged decompression and lateral mass screw fixation are proved to be effective in treating multi-segmental cervical spondylotic myelopathy associated with kyphosis, in terms of significant neurological function, maintaining the normal curvature and lower rate of axial symptoms and C5root palsy.