The Impact of Dynamic Alignment, Motion, and Center of Rotation on Myelopathy Grade and Regional Disability in Cervical Spondylotic Myelopathy

Abstract

Introduction Cervical stenosis is a defining feature of CSM. Matsunaga et al proposed that elements of stenosis are both static and dynamic, where the dynamic elements magnify the canal deformation of the static state. We hypothesize that dynamic motion may be associated with myelopathy severity and neck disability and present novel methods of dynamic motion analysis in CSM. Patients and Methods Post hoc analysis of a prospective, multicenter database of patients with CSM. A total of 110 patients (34%) met inclusion criteria symptomatic CSM, age over 18 years, baseline flexion/extension radiographs, and HRQOLs (mJOA, NDI, SF-36, and Nurick grade). The mean age was 57 ± 12 years with 41% female ( n = 46). Correlations with HRQOLs were analyzed for regional and focal parameters in flexion and extension. Baseline dynamic parameters (F/E cone relative to a fixed C7, center of rotation, range of motion arc relative to the COR) were also analyzed for correlations to HRQOLs. Results At baseline, the mean HRQOLs demonstrated disability and the mean radiographic parameters demonstrated sagittal malalignment. Among regional parameters, there was a significant correlation between increased C2–C7 angle in flexion and Nurick grade ( R = 0.189, p = 0.048) with no significant correlations in extension. Focal parameters including C7 slip were significantly correlated with disability (Flex R = −0.377, p = 0.003; Ext R = −0.261, p = 0.027). Reduced flexion/extension motion cones, a more posterior center of rotation, and smaller range of motion correlated with worse HRQOLs. Conclusion Dynamic motion analysis may play an important role in understanding CSM. Focal parameters demonstrated a significant correlation with worse HRQOLs especially C7 slip in flexion and extension. Novel methods of motion analysis demonstrated reduced motion cones correlated with worse myelopathy grades. More posterior center of rotation and smaller range of motion were both correlated with worse general health scores (PCS and Nurick).