The Correlation Between Clinical Outcomes And Postoperative Spinal Cord Drift After Decompressive Laminoplasty For Cervical Spondylotic Myelopathy

BackgroundCervical spondylosis is part of the aging process and affects most people if they live long enough. Degenerative changes affecting the intervertebral disks, vertebrae, facet joints, and ligamentous structures encroach on the cervical spinal canal and damage the spinal cord, especially in patients with a congenitally small cervical canal. Cervical spondylotic myelopathy (CSM) is the most common cause of myelopathy in adults. It's important to choose a suitable procedure, and there are widespread controversies about surgical approach nowadays, especially for the multilevel CSM. However, the surgery is generally performed to decompress the spinal cord and nerve root, no matter which approach it. Most of surgeons take spinal cord drift as a sign of succession decompression. "Bowstring principle", which used to explain the spinal cord drift for a long time, means that spinal cord is capable to get a biggest movement in cervical lord sis. According to this idea, most surgeons consider cervical hypnosis as the contraindication of posterior cervical spondylotic surgery. As the development of spinal surgery and MRI technology, this opinion is now being questioned by more and more experts.ObjectiveTo investigate the relationship among post decompressive migration of the spinal cord, clinical outcomes and preoperative cervical spine curvature.MethodsPreoperative and postoperative cervical spine MRIs of 45 patients who underwent cervical laminoplasty with/without fusion for the treatment of CSM were reviewed. Radiographic parameters including preoperative cervical spine curvature, spinal cord drift to the midpoint of the spinal cord were measured for statistical correlation. The recovery rate were based on the mJOA score, SF-36, VAS of the neck. ResultsFollow-up visit lasted from 6-48 months, with average of17.2 months. Statistical data were calculated as below:mJOA score was 10.87±3.16, SF-36 was 101.20±20.93, VAS of the neck was0.25±0.00, spinal cord drift (mm) was 1.39±0.88, postoperative cervical spine curvature were 19.98±14.98.According to application of spearman correlation analysis, no statistical correlation was revealed between post-decompressive spinal cord drift and clinical outcomes (spinal cord drift (mm) to mJOA score:N=0.10, P=0.54>0.05, to VAS of the neck:N=0.11, P=0.47>0.05, to SF-36:N=0.24, P=0.14>0.05). Also patients were divided into two groups according to spinal cord drift. The difference betweent mJOA,VAS of the neck,spinal cord drift (mm) of two groups was not statistically significant (p=0.547,p=0.201,p=0.334>0.05). The data shows that the preoperative cervical spine curvature did not statistically correlate with postoperative spinal cord drift.To discuss the relationship of spinal cord drift,cervical curvature and clinical outcomes, patients were divided into Normal-cervical-curvature Group and Abnormal-cervical-curvature Group. Analysis of the data did not reveal any statistical correlation between spinal cord drift and clinical outcomes(p=0.092,P=0.588,P=0.283>0.05).Patients were separated to Long-level Group (patients who received extensive and consecutive posterior laminoplasty) and Short-level Group (patients who received selected posterior decompression surgery). There was no significant difference between the subjects in Long-level Group and Short-level Group with respect to the mJOA recovery rate, sf-36, VAS of the neck, but the migration of the postoperative posterior drift of the spinal cord was greater for those in Long-level Group than for those in Short-level Group. There was no correlation between clinical outcomes and the length of surgery section.ConclusionsThe postoperative spinal cord drift in patients undergoing multisegmental decompressive laminoplasty with/without fusion for CSM does not statistically correlate with neither clinical outcomes nor preoperative cervical spine curvature. And there is no statistical correlation between preoperative cervical spine curvature and clinical outcomes. Although traditional extensive and consecutive laminoplasty resulted in a greater degree of shifting than did selected segmental laminoplasty, there was no difference found in the clinical outcomes between the two procedures. For multisegmental cervical spondylotic myelopathy, the traditional extensive and consecutive laminoplasty is not always necessary.