Dynamic Cervical Spinal Canal Stenosis: Identifying Imaging Risk Factors in Extended Positions

Study Design: A retrospective study at a single academic institution. Purpose: This study aimed to identify imaging risk factors for stenosis in extended neck positions undetectable in preoperative neutral magnetic resonance imaging (MRI) and improving decompression strategies for cervical spine disorders. Overview of Literature: Cervical disorders are influenced by various dynamic factors, with spinal stenosis appearing during neck extension. Despite the diagnostic value of dynamic cervical MRI, standard practice often uses neutral-position MRI, potentially influencing surgical outcomes. Methods: This study analyzed 143 patients who underwent decompression surgery between 2012 and 2014, who had symptomatic cervical disorders and MRI evidence of spinal cord or nerve compression but had no history of cervical spine surgery. Patient demographics, disease type, Japanese Orthopedic Association score, and follow-up periods were recorded. Spinal surgeons conducted radiological evaluations to determine stenosis levels using computed tomography myelography or MRI in neutral and extended positions. Measurements such as dural tube and spinal cord diameters, cervical alignment, range of motion, and various angles and distances were also analyzed. The residual space available for the spinal cord (SAC) was also calculated. Results: During extension, new stenosis frequently appeared caudal to the stenosis site in a neutral position, particularly at C5/C6 and C6/C7. A low SAC was identified as a significant risk factor for the development of new stenosis in both the upper and lower adjacent disc levels. Each 1-mm decrease in SAC resulted in an 8.9- and 2.7-fold increased risk of new stenosis development in the upper and lower adjacent disc levels, respectively. A practical SAC cutoff of 1.0 mm was established as the threshold for new stenosis development. Conclusions: The study identified SAC narrowing as the primary risk factor for new stenosis, with a clinically relevant cutoff of 1 mm. This study highlights the importance of local factors in stenosis development, advocating for further research to improve out-comes in patient with cervical spine disorders