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Myelopathy and Spinal Deformity: Relevance of Spinal Alignment in Planning Surgical Intervention for Degenerative Cervical Myelopathy

Shamji, Mohammed F., MD, PhD, FRCSC*; Ames, Christopher P., MD; Smith, Justin S., MD, PhD; Rhee, John M., MD§; Chapman, Jens R., MD; Fehlings, Michael G., MD, PhD, FRCSC*

doi: 10.1097/BRS.0b013e3182a7f521
Influence of Spinal Deformity on Management and Outcome of Cervical Spondylotic Myelopathy
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Surgical management of degenerative cervical myelopathy requires careful pathoanatomic consideration to select between various surgical options from both anterior and posterior approach. Hitherto, unexplored is the relevance of cervical deformity to the pathophysiology of such neurological disability, and whether correction of that deformity should be a surgical objective when planning for reconstruction after spinal cord decompression. Such correction could address both the static cord compression and the dynamic repetitive cord injury, while also restoring more normal biomechanics to the cervical spine. The articles in this focus issue's section on cervical spinal deformity reveal that cervical sagittal alignment is geometrically related to thoracolumbar spinal pelvic alignment and to T1 slope, and that it is further clinically correlated to regional disability and general health scores and to myelopathy severity. These conclusions are based on narrative reviews and a selection of primary research data, reflecting the nascency of this field. They further recommend for preoperative assessment of spinal alignment when significant deformity is suspected, and that correction of cervical kyphosis should be an objective when surgery is planned.

*Division of Neurosurgery, Toronto Western Hospital, Toronto, Ontario, Canada

UCSF Medical Center, Neurosurgery Clinic, San Francisco, CA

Department of Neurological Surgery, University of Virginia, Charlottesville, VA

§Department of Orthopaedic Surgery, Emory Spine Center, Atlanta, GA; and

UW Bone and Joint Center, Seattle, WA.

Address correspondence and reprint requests to Mohammed F. Shamji, MD, PhD, FRCSC, Toronto Western Hospital, Division of Neurosurgery, 399 Bathurst St, West Wing, 4th Flr, Room WW4-446, Toronto, Ontario, Canada M5T 2S8; E-mail: mohammed.shamji@uhn.ca

Acknowledgment date: June 10, 2013. First revision date: July 17, 2013. Acceptance date: July 25, 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: support for travel, board membership, consultancy, royalties, stock/stock options, grants/grants pending, provision of writing assistance, medicines, equipment, or administrative support, expert testimony, and payment for lectures.

The pathophysiology of degenerative cervical myelopathy is based on static spinal compression by structural changes stemming from either spondylosis (CSM) or heterotopic calcification (OPLL), but also on dynamic compression by nonphysiological excursion of the spinal cord and on cord tension related to its viscoelastic properties. It becomes intuitive then that cervical alignment can contribute to the onset and progression of myelopathy and consequently that restoration of sagittal and coronal alignment should be reasonable objectives when considering surgical intervention for this disease. The articles in this section provide an overview of the interplay with cervical spine alignment and pathophysiology and outcomes of myelopathy management.

Cervical deformity in the sagittal plane can arise from the underlying disease process, such as with spondylosis altering anterior column integrity with consequent loss of disc height, listhetic changes, and kyphosis. Surgical interventions such as laminectomy and laminoplasty may also produce iatrogenic progression of myelopathy in those individuals who develop postsurgical kyphosis. Indeed, patients with kyphotic or neutral postoperative sagittal alignment also are predisposed to the onset of clinical adjacent segment pathology once a fusion operation for myelopathy is undertaken.1 How this malalignment contributes to symptomatic progression remains an elusive answer, but what we have learned is well described in this issue by Ames and Smith.

The narrative review by Ames and coworkers describes the standard measurements for global sagittal alignment with specific focus on the varied cervical parameters. Correlations between cervical lordosis and the T1 slope underscore the research objectives of evaluating global sagittal alignment in planning and outcomes analysis from cervical spine fusion procedures.2–4 The proposed hypothesis is that malalignment may contribute to myelopathy via radial compression and longitudinal tension of the spinal cord, with simple decompression not necessarily decreasing the latter in the deformed spine.5 Consequent changes of demyelination and neuronal loss can translate this into clinically-significant deficit.4,6

Smith and coworkers provide new insight into how alignment correlates with neurological outcomes after management of CSM based on the AOSpine North America prospective multicenter CSM study. They introduce novel magnetic resonance imaging-based metrics of in vivo spinal cord dimensions, applying them to find associations between spinal cord cross-sectional area, length, and volume with myelopathy severity. Among patients deemed surgical, their novel data reveal that alignment does associate with extent of neurological dysfunction; the implications of these findings for the ideal surgical correction warrants future investigation. This report is also the first to correlate sagittal balance (C2–C7 sagittal vertical axis) with severity of myelopathy in CSM.

Although it is intuitive that correction of cervical deformity could address both static spinal cord compression and dynamic repeated concussive and tension forces, this nascent field has significant voids to fill insofar as how to define the ideal postsurgical alignment, and what surgical approaches can best achieve those objectives. Further research must focus on prospective assessment of how changes in cervical alignment will impact postoperative recovery from myelopathy and improvement in neck-related disability. It will be important to investigate how cervical malalignment impacts biomechanically on neck pain (e.g., VAS neck) and neurologically on myelopathy progression (e.g., mJOA).

Summary Statements.

Statement 1: Cervical sagittal alignment (cervical SVA and kyphosis) is related to thoracolumbar spinal pelvic alignment and to T1 slope.

Statement 2: When significant deformity is clinically or radiographically suspected, regional cervical and relative global spinal alignment should be evaluated preoperatively via standing 3-ft scoliosis radiographs for appropriate operative planning.

Statement 3: Cervical sagittal alignment (C2–C7 SVA) is correlated to regional disability and general health scores and to myelopathy severity.

Statement 4: When performing decompressive surgery for CSM, consideration should be given to correction of cervical kyphosis and cervical sagittal imbalance (C2–C7 SVA) when present.

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Acknowledgments

M.F.S: Study design, data analysis and interpretation, manuscript preparation, and revision; C.A: Study design, data analysis and interpretation, and manuscript revision; J.S.S: Study design, data analysis and interpretation, manuscript preparation, and revision; J.R: Study design, data analysis and interpretation, manuscript preparation, and revision; J.C: Study design, data analysis and interpretation, manuscript preparation, and revision; M.G.F: Study design, data analysis and interpretation, manuscript preparation, and revision.

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References

1. Hansen MA, Kim HJ, Van Alstyne EM, et al. Does postsurgical cervical deformity affect the risk of cervical adjacent segment pathology? A systematic review. Spine 2012;37:S75–84.
2. Hardacker JW, Shuford RF, Capicotto PN, et al. Radiographic standing cervical segmental alignment in adult volunteers without neck symptoms. Spine 1997;22:1472–80; discussion 80.
3. Lafage V, Schwab FJ, Skalli W, et al. Standing balance and sagittal plane spinal deformity: analysis of spinopelvic and gravity line parameters. Spine 2008;33:1572–8.
4. Tang JA, Scheer JK, Smith JS, et al. The impact of standing regional cervical sagittal alignment on outcomes in posterior cervical fusion surgery. Neurosurgery 2012;71:662–9; discussion 9.
5. Chavanne A, Pettigrew DB, Holtz JR, et al. Spinal cord intramedullary pressure in cervical kyphotic deformity: a cadaveric study. Spine 2011;36:1619–26.
6. Shimizu K, Nakamura M, Nishikawa Y, et al. Spinal kyphosis causes demyelination and neuronal loss in the spinal cord: a new model of kyphotic deformity using juvenile Japanese small game fowls. Spine 2005;30:2388–92.
Keywords:

myelopathy; spinal deformity; sagittal alignment; kyphosis; spinal imaging; spinal biomechanics

© 2013 by Lippincott Williams & Wilkins