The correlation between preoperative compression degree of the spinal cord assessed by magnetic resonance imaging and the results of surgery for cervical spondylotic myelopathy

English Keywords:Cervical spondylotic myelopathy  Cervical spine  Magnetic resonance imaging  Compression degree of the spinal cord  Recovery rate

English Abstract:

  【Abstract】 Objectives: To investigate the correlation between preoperative compression degree of the spinal cord assessed by magnetic resonance imaging and the results of surgery for cervical spondylotic myelopathy. Methods: From February 2006 to July 2010, 115 patients with cervical spondylotic myelopathy in Peking University Third Hospital undergoing anterior or posterior decompression were included in this study. There were 75 males and 40 females with the age ranged from 24 to 85 years(average, 56 years). All patients were followed up for at least 24 months(average, 29 months). The number of compression levels was measured on T2-weighted sagittal MRI, then the ratio of the sagittal diameter of the spinal cord to the sagittal diameter of the dural sac was calculated as MRI Pavlov ratio at the site of maximal cord compression. The transverse area, transverse diameter and sagittal diameter of the spinal cord and the dural sac at the site of maximal cord compression were measured on T2-weighted axial MRI. Then the occupation ratio was calculated as the ratio of the area of the spinal cord to the area of the dural sac, the sagittal/transverse occupation ratio was calculated as the ratio of the sagittal/transverse diameter of the spinal cord to the sagittal/transverse diameter of the dural sac as percentage. The severity of myelopathy was evaluated by the modified Japanese Orthopaedic Association(mJOA) score, and recovery was determined by recovery rate(RR). Imaging fidings and preoperative mJOA(pre-mJOA) score were then correlated with 24-month postoperative mJOA(post-mJOA) score and RR. Then a linear regression analysis was established regarding the 24-month post-mJOA score and RR as dependent variables, and the predictive RR was correlated with the actual RR. Results: The spinal cord was compressed at 1 level in 37 cases, 2 levels in 17 cases, 3 levels in 15 cases, 4 levels in 25 cases and 5 levels in 21 cases. The MRI Pavlov ratio was 0.426±0.097, the sagittal and the transverse occupation ratio was (79.1±8.4)% and (76.2±7.3)%, and the occupation ratio was (54.6±16.2)%. The mJOA score increased from the preoperative 12.1±2.9 to the postoperative 14.7±2.0(P<0.001), and the RR was (43.0±55.7)%[(-200%)-100%]. The post-mJOA score and the RR correlated significantly with the pre-mJOA score, the MRI Pavlov ratio and the sagittal occupation ratio(P<0.05), but not correlated with the occupation ratio or the transverse occupation ratio significantly(P>0.05). The multiple regression equations to predict the results of surgery were as follows: post-mJOA=4.202+0.346×pre-mJOA+4.973×MRI Pavlov ratio+0.053×sagittal occupation ratio(%); RR=-30.348+ 115.875×MRI Pavlov ratio+1.226×sagittal occupation ratio(%)-5.993×pre-mJOA. The predictive and actual RRs were correlated significantly(R2=0.138, P<0.001). Conclusions: The compression degree of the spinal cord at the sagittal plane assessed preoperatively by MRI correlates significantly with the surgical effects of cervical spondylotic myelopathy.