| Objective: To study the relationship between posterior shift of spinal cord and clinical curative after posterior decompression on the patients with cervical spondylotic myelopathy and to discuss mechanism of posterior shift of spinal cord.Methods: 1. We chosed 47 patients (31 men and 16 women) who underwent posterior decompression in our hospital from Sept. 2006 to Oct. 2010. The areas of decompression were from C3 to C6 (19 cases), C2 to C6 (1 case), and C3 to C7 (27 cases), while there were expansive single door laminoplasty(27 cases) and laminectomy(20 cases). The preoperative and postoperative 6 months spinal cord function was evaluated using Japanese orthopaedic society (JOA) rating criteria.2. The distance of posterior spinal cord migration were compared between laminoplasty and laminectomy.3. Using MRI imaging on central sagittal T2-weighted images are measurements preoperative cervical alignment, spinal cord ventral average oppression rate, longitudinal distance index,expanded laminae length,compression diameter of the largest segment and posterior spinal cord migration; Grouped according to posterior shift of spinal cord,≥3mm was group A and 0-3mm was group B. The age, duration, preoperative JOA score, compression diameter of the largest segment of AB groups were assessed with balancing test to assess JOA score recovery rate and good rate of the two groups, using t-test and a chi-square test. Correlation analysis were done to explore the relationship between posterior shift of spinal cord and the curative effect; The radiographic parameters were compared between group A and B.The relationshp between four radiographic parameters and posterior shift of spinal cord were also analyzed.Results: 1 JOA score before surgery and after 6 months: preoperative JOA score of the patients was 9.21±1.84, in contrast, JOA score at follow-up 6 months was 13.87±1.79, and the improvement of JOA score was 61.05%, including excellent in 12 cases, good in 22 cases and effective in 13 cases. Excellent and good rate is 72.34%.2 There were no statistically significant difference between laminoplasty and laminectomy.3 According to the age, disease duration, preoperative JOA score, T2 high signal and compression diameter of the largest segment, there was no statistically significant difference between two samples using t test (P> 0.05). JOA score recovery rate after surgery in the different groups were as follows: 78.81±15.30% in the A group and 52.73±12.12% in the B group. There were statistically significant difference between group A and B (P< 0.01). Compared the excellent and good rate of AB group, there was statistically significant difference. Posterior shift of spinal cord and JOA score recovery rate were analyzed by correlation, r=0.667(P<0.01), there was positive linear correlation. The cervical alignment and Spinal cord ventral average oppression rate were statistically significant difference between group A and B (P< 0.05), The expanded laminae length and LDI were no statistically significant difference between group A and B (P< 0.05). Pearson correlation analysis of spinal cord drift and radiographic parameter showed that: cervical spine Angle and posterior shift of spinal cord correlation coefficient r=0.408(P< 0.05) ,there were statistically significant linear relationship. Based on spinal cord ventral average oppression rate and Spinal cord drift correlation coefficient r=0.439(P<0.05), there was positive linear relationship. To decompression segment length and posterior shift of spinal cord correlation coefficient r=-0.081(P>0.05),there was no statistically significant linear relationship. To longitudinal distance index and posterior shift of spinal cord correlation coefficient r=-0.222(P>0.05),there were no statistically significant linear relationship; By the multiple linear regression, posterior shift of spinal cord was correlated between spinal cord ventral average oppression rate and cervical spine Angle.Conclusions: 1 Decompression segment within an average of spinal cord drift and clinical result after cervical posterior decompression have significant correlation, the recovery of the spinal cord function is better when the range of posterior shift of spinal cord is 3mm-4mm.2 Mechanism of spinal cord drift may be relevant with spinal cord ventral average oppression rate and bow string theory after posterior spinal surgery.
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