title: Impact of dynamic alignment, motion, and center of rotation on myelopathy grade and regional disability in cervical spondylotic myelopathy.
abstract: OBJECTIVE
  Cervical stenosis is a defining feature of cervical spondylotic myelopathy (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. For the current study, the authors hypothesized that dynamic changes may be associated with myelopathy severity and neck disability. This goal of this study was to present novel methods of dynamic motion analysis in CSM.
  
  
  METHODS
  A post hoc analysis was performed of a prospective, multicenter database of patients with CSM from the AOSpine North American study. One hundred ten patients (34%) met inclusion criteria, which were symptomatic CSM, age over 18 years, baseline flexion/extension radiographs, and health-related quality of life (HRQOL) questionnaires (modified Japanese Orthopaedic Association [mJOA] score, Neck Disability Index [NDI], the 36-Item Short Form Health Survey Physical Component Score [SF-36 PCS], and Nurick grade). The mean age was 56.9 ± 12 years, and 42% of patients were women (n = 46). Correlations with HRQOL measures were analyzed for regional (cervical lordosis and cervical sagittal vertical axis) and focal parameters (kyphosis and spondylolisthesis between adjacent vertebrae) in flexion and extension. Baseline dynamic parameters (flexion/extension cone relative to a fixed C-7, center of rotation [COR], and range of motion arc relative to the COR) were also analyzed for correlations with HRQOL measures.
  
  
  RESULTS
  At baseline, the mean HRQOL measures demonstrated disability and the mean radiographic parameters demonstrated sagittal malalignment. Among regional parameters, there was a significant correlation between decreased neck flexion (increased C2-7 angle in flexion) and worse Nurick grade (R = 0.189, p = 0.048), with no significant correlations in extension. Focal parameters, including increased C-7 sagittal translation overT-1 (slip), were significantly correlated with greater myelopathy severity (mJOA score, Flexion R = -0.377, p = 0.003; mJOA score, Extension R = -0.261, p = 0.027). Sagittal slip at C-2 and C-4 also correlated with worse HRQOL measures. Reduced flexion/extension motion cones, a more posterior COR, and smaller range of motion correlated with worse general health SF-36 PCS and Nurick grade.
  
  
  CONCLUSIONS
  Dynamic motion analysis may play an important role in understanding CSM. Focal parameters demonstrated a significant correlation with worse HRQOL measures, especially increased C-7 sagittal slip in flexion and extension. Novel methods of motion analysis demonstrating reduced motion cones correlated with worse myelopathy grades. More posterior COR and smaller range of motion were both correlated with worse general health scores (SF-36 PCS and Nurick grade). To our knowledge, this is the first study to demonstrate correlation of dynamic motion and listhesis with disability and myelopathy in CSM.
authors: Department of Orthopaedic Surgery, New York University Hospital for Joint Diseases, New York, New York;
authors: Shian
authors: S
authors: Liu
authors: Department of Orthopaedic Surgery, New York University Hospital for Joint Diseases, New York, New York;
authors: Renaud
authors: R
authors: Lafage
authors: Department of Neurosurgery, University of Virginia Medical Center, Charlottesville, Virginia;
authors: Justin S
authors: JS
authors: Smith
authors: Department of Orthopaedic Surgery, New York University Hospital for Joint Diseases, New York, New York;
authors: Themistocles S
authors: TS
authors: Protopsaltis
authors: Department of Orthopaedic Surgery, New York University Hospital for Joint Diseases, New York, New York;
authors: Virginie C
authors: VC
authors: Lafage
authors: Department of Orthopaedic Surgery, New York University Hospital for Joint Diseases, New York, New York;
authors: Vincent
authors: V
authors: Challier
authors: Department of Neurosurgery, University of Virginia Medical Center, Charlottesville, Virginia;
authors: Christopher I
authors: CI
authors: Shaffrey
authors: Rothman Institute, Egg Harbor Township, New Jersey;
authors: Kris
authors: K
authors: Radcliff
authors: Department of Neurosurgery, University of Kansas Medical Center, Kansas City, Kansas;
authors: Paul M
authors: PM
authors: Arnold
authors: Department of Orthopaedic Surgery, University of Washington, Seattle, Washington;
authors: Jens R
authors: JR
authors: Chapman
authors: Department of Orthopaedic Surgery, New York University Hospital for Joint Diseases, New York, New York;
authors: Frank J
authors: FJ
authors: Schwab
authors: Department of Neurosurgery, Toronto Western Hospital, Toronto, Ontario, Canada;
authors: Eric M
authors: EM
authors: Massicotte
authors: Emory Orthopaedics and Spine Center, Emory University School of Medicine, Atlanta, Georgia; and.
authors: S Tim
authors: ST
authors: Yoon
authors: Department of Neurosurgery, Toronto Western Hospital, Toronto, Ontario, Canada;
authors: Michael G
authors: MG
authors: Fehlings
authors: Department of Neurosurgery, University of California-San Francisco Medical Center, San Francisco, California.
authors: Christopher P
authors: CP
authors: Ames
mesh_terms: D000328:Adult; D000368:Aged; D002574:Cervical Vertebrae; D004185:Disability Evaluation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011788:Quality of Life; D016059:Range of Motion, Articular; D013118:Spinal Cord Diseases / Q000175:diagnosis* / Q000209:etiology* / Q000503:physiopathology; D055009:Spondylosis / Q000150:complications* / Q000175:diagnosis / Q000503:physiopathology*
keywords: 7 cervical lordosis; COR = center of rotation; 7 sagittal vertical axis; CSM = cervical spondylotic myelopathy; CTJ = cervicothoracic junction; HRQOL = health-related quality of life; NDI = Neck Disability Index; ROM = range of motion; SF-36 PCS = 36-Item Short Form Health Survey Physical Component Summary; cL = C2; cSVA = C2; cervical spondylotic myelopathy; cone of kinesis; dynamic alignment; extension; flexion; health-related quality of life outcomes; mJOA = modified Japanese Orthopaedic Association