Changes Of Sagittal Balance Of Cervical Spine After Anterior Cervical Discectomy Fusion In Double Segment Of Cervical Spondylotic Myelopathy

Objective: Cervical spondylotic myelopathy(CSM),compressed by static and dynamic factors due to unstable state of vertebral body, was characterized by abnormal of sensation and motion. It usually damaged multilevel discs of cervical spine and mostly occurs in the victims aging between 40 and 60 years. The sagittal balance of cervical spine recently is crucial to the incidence of cervical spondylotic and the severity of unstable state can be estimated by the sagittal parameters of cervical alignment. However, the parameters of sagittal cervical alignment can be limited by the unclear X-ray graph, the differences in the position of radioactive examination and orthopedic surgery, insufficient studies about the changes of sagittal balance of cervical spine in double segment of CSM after anterior cervical operation. The purpose of such study is to measured parameters of sagittal cervical alignment by the sagittal reconstruction of Cervical Computed Tomographic Scans and analyze changes in the clinical and radiolographic factors related to cervical sagittal balance in patients with Cervical spondylotic myelopathy after anterior cervical surgery.Methods: This retrospective comparative study assessed prospectively collected data obtained from 58 patients with C5-6、C6-7 Cervical Spondylotic Myelopathy from January 2012 to July 2014 at our department. Cervical myelopathy demonstrating cord compression by MRI was identical to the clinical examination. Inclusion criterion included the following:1. patients with significant neurological symptoms in spite of conservative treatment for at least 3 months; 2. patients of acute exacerbation lead by trauma and other factors; 3. patients who has spinal segment unsteadily with severe neck pain and dysfunction of limb movement. Exclusion criterion included that: patients who underwent previous cervical spine operation; 2 patients suffered from bony destruction,active inflammation of verterbal body and the diseases that were unsuitable to surgery; 3.patients with spinal cord degeneration and amyotrophy. A total of 56 patients were enrolled in this study. All the patients underwent anterior cervical discectomy fusion. Patients’ scheduled regular follow-up visits were at 1, 3, 6, and 12 months, and then annually.All patients were measured clinically and radiographic parameters preoperative and during follow-up, while the radiographic data obtained from the sagittal reconstruction of Cervical CT which should shown the manubrium and first thoracic vertebra completely. Analyzed the parameters preoperatively and during follow-up, the radiographic parameters shown by the sagittal reconstruction of cervical CT including T1 slope, C2-7 SVA(C2-7 sagittal vertical axis) and C2-7 Cobb angle. The clinical parameters were neck VOA(Visual Analogue Scale), upper limb VOA and cervical JOA(Japanese Orthopedic Association).Patients were divided into two groups based on the median of T1 slope’s scope preoperatively, that patients in high T1 slope team was above the median, while patients in low T1 slope team was blow the median; compare the clinical and radiographic differences between the two groups. Finally We compare the postoperative differences between the radiographic and clinical data as well as explored the correlation between the means of each radiographic data, the means of radiographic and clinical data. Data were analyzed by the Statistical Package for the Social Sciences(version 16.0), the bilate P-value <0.05 was considered to be statistically significant.Results: A total of 56 patients were enrolled in this study. Demographic Data:the mean age of the patients was 60.9 years(range, 40-78 years). 38 patients were men, and 18 patients were women. The mean follow-up period was 29.1 months(range, 12-36 months). In the analysis of postoperative changes of parameters of sagittal balance of cervical alignment, the C2-7 SVA decreased from 25.16±1.0 mm to 20.75±1.64 mm, the C2-7 Cobb angle increased from 19.20±1.04 degrees to 24.05±0.84 degrees, and the T1 slope increased from 23.38 ± 4.27 mm to 25.66 ± 2.09 mm. All postoperative changes of parameters of sagittal balance of cervical alignment showed statistically significance(P<0.01). In the analysis of changes in clinical parameters after surgery, the neck VAS decreased from 4.14±0.84 to 2.34±1.49, the upper limb VAS decreased from 1.35±0.94 to 1.04±0.87, the cervical JOA increased from 10.14±2.68 to 14.77±1.70. The neck VAS and cervical JOA were changed significantly after operation(P<0.01), but no statistically significance change in upper limb VAS(P=0.82). Patients were divided into two groups based on median of T1 slope’s scope before surgery. The spinal cord fuction of two group has improved,JOA increased from 10.14±2.46 to 14.77±1.70 during follow-up. The high T1 slope( range 23.4 to 43.6°, mean 26.65±3.47°) included 28 patients with 18 male, 10 female and the average age was 61.66±7.31 years. The low T1 slope( range 12.7 to 23.4°, mean 20.13±1.76°) included 28 patients with 20 male and 8 female,the average age was 60.14±7.83 years. The age and sex ratio were no statistical significant(P=0.74)(P=0.62). In the comparison of sagittal parameters of cervical spine, High T1 slope had postoperative high C2-7 SVA(21.68±1.12) than low T1 slope(19.82±1.56)(P<0.01); High T1 slope had postoperative low C2-7 Cobb( 24.18±0.60) than low T1 slope( 23.93±1.04),(P=0.89)。In the comparison of clinical improvement,High T1 slope had postoperative low JOA( 13.89±1.91), JOA improvement( 52.8%) than low T1 slope( 15.64 ± 0.83),( 78.7%) and thus is statistical significant( P<0.01);High T1 slope had low VAS( 2.00±1.49),upper limb VAS( 0.75±0.84) than low T1 slope( 2.68±1.44),( 1.32±0.82),thus is no statistical significant( P=0.66),( P=0.31). In the analysis of correlation between the means of each parameters of sagittal balance of cervical alignment, there were significantly negative correlations between C2-7 SVA and C2-7 Cobb(r=-0.45, P<0.01) and positive correlation between C2-7 Cobb and T1 slope(r=0.26,P<0.01). In the analysis of correlation between the means of radiographic and clinical parameters, there were negative correlations between C2-7 SVA and cervical JOA(r=-0.31,P<0.01), C2-7 SVA and cervical JOA improvement(r=- 0.17,P<0.01), C2-7 Cobb and neck VAS(r=-0.42,P<0.01)Conclusion: The parameters of sagittal balance of cervical alignment impact on cervical balance intensively. In a patient without the destruction of posterior cervical alignment, cervical lordosis increased to compensate the cervical slippage caused by the increased T1 slope.ACDF surgery may make lower risk in slippage, and increase cervical lordosis by additional process. The parameters of sagittal balance of cervical alignment may predict the clinical improvement of patients after surgery. In the investigation of comparison, patients with higher T1 slope may have lower improvement after surgery. The surgeons in spine department should take a deep awareness of sagittal parameters and make customized surgery which evaluate the severity of unstable cervical preoperatively.