Association of Myelopathy Scores With Cervical Sagittal Balance and Normalized Spinal Cord Volume: Analysis of 56 Preoperative Cases From the AOSpine North America Myelopathy Study

Smith, Justin S. MD, PhD*; Lafage, Virginie PhD; Ryan, Devon J. BA; Shaffrey, Christopher I. MD*; Schwab, Frank J. MD; Patel, Alpesh A. MD; Brodke, Darrel S. MD§; Arnold, Paul M. MD; Riew, K. Daniel MD; Traynelis, Vincent C. MD**; Radcliff, Kris MD††; Vaccaro, Alexander R. MD, PhD††; Fehlings, Michael G. MD, PhD‡‡; Ames, Christopher P. MD§§

doi: 10.1097/BRS.0b013e3182a7eb9e
Influence of Spinal Deformity on Management and Outcome of Cervical Spondylotic Myelopathy

Study Design. Post hoc analysis of prospectively collected data.

Objective. Development of methods to determine in vivo spinal cord dimensions and application to correlate preoperative alignment, myelopathy, and health-related quality-of-life scores in patients with cervical spondylotic myelopathy (CSM).

Summary of Background Data. CSM is the leading cause of spinal cord dysfunction. The association between cervical alignment, sagittal balance, and myelopathy has not been well characterized.

Methods. This was a post hoc analysis of the prospective, multicenter AOSpine North America CSM study. Inclusion criteria for this study required preoperative cervical magnetic resonance imaging (MRI) and neutral sagittal cervical radiography. Techniques for MRI assessment of spinal cord dimensions were developed. Correlations between imaging and health-related quality-of-life scores were assessed.

Results. Fifty-six patients met inclusion criteria (mean age = 55.4 yr). The modified Japanese Orthopedic Association (mJOA) scores correlated with C2–C7 sagittal vertical axis (SVA) (r = −0.282, P = 0.035). Spinal cord volume correlated with cord length (r = 0.472, P < 0.001) and cord average cross-sectional area (r = 0.957, P < 0.001). For all patients, no correlations were found between MRI measurements of spinal cord length, volume, mean cross-sectional area or surface area, and outcomes. For patients with cervical lordosis, mJOA scores correlated positively with cord volume (r = 0.366, P = 0.022), external cord area (r = 0.399, P = 0.012), and mean cross-sectional cord area (r = 0.345, P = 0.031). In contrast, for patients with cervical kyphosis, mJOA scores correlated negatively with cord volume (r = −0.496, P = 0.043) and mean cross-sectional cord area (r = −0.535, P = 0.027).

Conclusion. This study is the first to correlate cervical sagittal balance (C2–C7 SVA) to myelopathy severity. We found a moderate negative correlation in kyphotic patients of cord volume and cross-sectional area to mJOA scores. The opposite (positive correlation) was found for lordotic patients, suggesting a relationship of cord volume to myelopathy that differs on the basis of sagittal alignment. It is interesting to note that sagittal balance but not kyphosis is tied to myelopathy score. Future work will correlate alignment changes to cord morphology changes and myelopathy outcomes.

Summary Statements. This is the first study to correlate sagittal balance (C2–C7 SVA) to myelopathy severity. We found a moderate negative correlation in kyphotic patients of cord volume and cross-sectional area to mJOA scores. The opposite (positive correlation) was found for lordotic patients, suggesting a relationship of cord volume to myelopathy that differs on the basis of sagittal alignment.

Novel techniques were developed to determine in vivo spinal cord dimensions on the basis of magnetic resonance imaging and applied and correlated to preoperative alignment, myelopathy, and disability scores in patients with cervical spondylotic myelopathy (CSM). The findings include the first report to correlate cervical sagittal balance (C2–C7 sagittal vertical axis) to myelopathy severity in CSM.

*Department of Neurosurgery, University of Virginia, Charlottesville

Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York

Department of Orthopaedic Surgery, Northwestern University, Chicago, IL

§Department of Orthopaedic Surgery, University of Utah, Salt Lake City

Department of Neurosurgery, University of Kansas, Kansas City

Department of Orthopaedic Surgery, Washington University, St Louis, MO

**Department of Neurosurgery, Rush Medical Center, Chicago, IL

††Department of Orthopaedic Surgery, Thomas Jefferson University, Philadelphia, PA

‡‡Division of Neurosurgery and Spinal Program, University of Toronto, Toronto, Ontario, Canada; and

§§Department of Neurological Surgery, University of California, San Francisco.

Address correspondence and reprint requests to Justin S. Smith, MD, PhD, Department of Neurosurgery, University of Virginia Health Sciences Center, P.O. Box 800212, Charlottesville, VA 22908; E-mail: jss7f@virginia.edu

Acknowledgment date: March 24, 2013. First revision date: June 1, 2013. Second revision date: July 28, 2013. Acceptance date: July 29, 2013.

The manuscript submitted does not contain information about medical device(s)/drug(s).

Supported by AOSpine North America, Inc. Analytic support for this work was provided by Spectrum Research, Inc., with funding from the AOSpine North America.

Relevant financial activities outside the submitted work: grant, support for travel, provision of writing assistance, medicines, equipment, or administrative support, board membership, consultancy, expert testimony, grants/grants pending, payment for lectures, stock/stock options, expert testimony, patents, royalties, payment for development of educational presentations, and travel/accommodations/meeting expenses.

© 2013 by Lippincott Williams & Wilkins