Magnetic Resonance Imaging of the Cervical Spine Under-Represents Sagittal Plane Deformity in Degenerative Myelopathy Patients

Background In treating patients with cervical myelopathy, surgical approach may be dictated by sagittal balance, highlighting the need for accurate pre-operative assessment. Magnetic Resonance Imaging (MRI) is widely-recognized for its utility in the diagnosis and surgical planning of cervical myelopathy. Plain radiographs (X-rays) are a reliable tool to assess bony alignment. However, they may not always be included in standard pre-operative evaluation, especially in an era of restricted payer-environments. Failure to appropriately acknowledge a patients' preoperative kyphotic deformity may cause the surgeon to choose a posterior-only approach, which would provide suboptimal sagittal plane correction and decompression of anterior pathology. Methods 101 patients with cervical myelopathy with MRI and plain radiographs were identified. Cervical lordosis and kyphosis were measured using the Cobb method on standing lateral x-ray and sagittal T2-weighted MRI. CI (Ishihara) was also measured on standing lateral x-ray, and sagittal T2-weighted MRI. Bland-Altman plots were generated and used to compare subtle differences in measurement techniques and modalities. Odom's criteria were recorded. Results The average difference between plain radiograph and MRI measurements for curvature angle was 3.5 +/- 7.2 degrees (p < 0.001), and the average difference between plain radiograph and MRI measurements for curvature index was 1.5 +/- 5.9 degrees (p= 0.015). Conclusions MRI may under-represent the respective sagittal plane deformity in patients with degenerative cervical myelopathy. Clinical Relevance We would recommend the use of standing x-rays when considering surgical planning in all myelopathy patients. This manuscript was reviewed and approved by an institutional review board. Informed consent was not obtained because patient specific identifying information was not used. It was performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments.