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Computerized Tomographic Morphometric Analysis of Subaxial Cervical Spine Pedicles in Young Asymptomatic Volunteers
Raj D. Rao, MD1; Satyajit V. Marawar, MD1; Brian D. Stemper, PhD1; Narayan Yoganandan, PhD1; Barry S. Shender, PhD2
1 Departments of Orthopaedic Surgery (R.D.R. and S.V.M.) and Neurosurgery (B.D.S. and N.Y.), Medical College of Wisconsin, 9200 West Wisconsin Avenue, Milwaukee, WI 53226. E-mail address for R.D. Rao: rrao@mcw.edu
2 Aerospace Medical Association, Code 4656, Building 2187, Suite 2280A, Naval Air Warfare Center Aircraft Division, 48110 Shaw Road Unit 5, Patuxent River, MD 20670
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Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from the United States Office of Naval Research, Department of Defense, through Naval Air Warfare Center Aircraft Division contract N00421-02-C-3005 and the Department of Veterans Affairs Medical Research. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.
Investigation performed at the Department of Orthopaedic Surgery, the Medical College of Wisconsin, Milwaukee, Wisconsin

The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2008 Sep 01;90(9):1914-1921. doi: 10.2106/JBJS.G.01166
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Background: Although cervical spine pedicle screws have been shown to provide excellent fixation, widespread acceptance of their use is limited because of the risk of injury to the spinal cord, nerve roots, and vertebral arteries. The risks of pedicle screw insertion in the cervical spine can be mitigated by a three-dimensional appreciation of pedicle anatomy. Normative data on three-dimensional subaxial pedicle geometry from a large, young, and asymptomatic North American population are lacking. The purpose of the present study was to determine three-dimensional subaxial pedicle geometry in a large group of young volunteers and to determine level and sex-specific morphologic differences.

Methods: Helical computerized tomography scans were made from the third cervical to the seventh cervical vertebra in ninety-eight volunteers (sixty-three men and thirty-five women) with an average age of twenty-five years. Pedicle width, height, length, and transverse and sagittal angulations were measured bilaterally. Pedicle screw insertion positions were quantified in terms of mediolateral and superoinferior offsets relative to readily identifiable landmarks.

Results: The mean pedicle width and height at all subaxial levels were sufficient to accommodate 3.5-mm screws in 98% of the volunteers. Pedicle width and height dimensions of <4.0 mm were rare (observed in association with only 1.7% of the pedicles), with 82% occurring in women and 72% occurring unilaterally. Screw insertion positions generally moved medially and superiorly at caudal levels. Transverse angulation was approximately 45° at the third to fifth cervical levels and was less at more caudal levels. Sagittal angulation changed from a cranial orientation at superior levels to a caudal orientation at inferior levels. Mediolateral and superoinferior insertion positions and sagittal angulations were significantly dependent (p < 0.05) on sex and spinal level. Transverse angulation was significantly dependent (p < 0.05) on spinal level.

Conclusions: Pedicle screw insertion points and orientation are significantly different (p < 0.05) at most subaxial cervical levels and between men and women. Preoperative imaging studies should be carefully templated for pedicle size in all patients on a level-specific basis. Although the prevalence was low, women were more likely to have pedicle width and height dimensions of <4.0 mm.

Clinical Relevance: The present study provides normative data on subaxial cervical pedicle geometry from a large sample of young, healthy men and women. The data may be useful for preoperative planning for pedicle screw fixation.

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    Accreditation Statement
    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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