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Posterior Stabilization at the Cervicothoracic Junction: A Biomechanical Study

Kreshak, Jennifer L. MD*; Kim, Daniel H. MD†; Lindsey, Derek P. MS‡; Kam, Andrew C. MD§; Panjabi, Manohar M. PhD*; Yerby, Scott A. PhD‡∥¶

Biomechanics

Study Design. This study biomechanically evaluated three fixation devices for stability with posterior two- and three-column injuries.

Objectives. To find an effective means of posteriorly stabilizing injuries at the cervicothoracic junction.

Summary of Background Data. The cervicothoracic spine is complex anatomically and has been a difficult challenge in approach and stabilization of traumatic and degenerative disorders.

Methods. Twenty-one human cadaveric spines (C3–T3) were loaded in flexion, extension, lateral bending, and axial torsion. A posterior two-column injury was created at C7–T1. One of three posterior fixation systems was applied (two rod–screw systems, one plate–screw system, all with screws at C5, C6 and T1, T2). The spines were tested again. A three-column injury was created by transecting the remaining anterior structures; the spines were tested a final time.

Results. In flexion–extension, there were no significant differences in stiffness between intact and instrumented two-column injury specimens for all systems; the instrumented three-column injury was significantly (P < 0.05) less stiff than intact specimens in extension. Ranges of motion and neutral zones decreased from intact to instrumented two-column injuries and increased from intact to three-column constructs. In lateral bending and axial rotation, all systems were stiffer than intact spines for both injuries; ranges of motion and neutral zones were reduced for both injuries compared with intact specimens.

Conclusion. All three systems stabilize the cervicothoracic junction with a posterior two-column injury in flexion–extension, lateral bending, and axial rotation; none was adequate for a three-column injury, particularly in extension. A three-column injury at this level would warrant supplemental anterior fixation.

From the *Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, Connecticut,

the †Department of Neurosurgery, Stanford University School of Medicine, Stanford, California,

‡VA Palo Alto RR&D Center, Palo Alto, California,

the §Department of Neurosurgery, Westmead Hospital, Westmead, New South Wales, Australia,

∥St. Francis Medical Technologies, Concord, California,

and ¶San Francisco Orthopaedic Residency Program, San Francisco, California.

Supported in part by a grant from the North American Spine Society and a Yale Medical Student Research Fellowship.

Acknowledgment date: August 7, 2001.

First revision date: May 7, 2002.

Acceptance date: May 13, 2002.

Equipment was provided by Synthes Cervifix (Paoli, PA), DePuy Summit (Warsaw, IN), and Danek Axis (Minneapolis, MN). The device(s) is/are FDA approved.

Address correspondence to Manohar M. Panjabi, PhD, Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, P.O. Box 208071, New Haven, CT 06520-8071; E-mail: manohar.panjabi@yale.edu

© 2002 Lippincott Williams & Wilkins, Inc.