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Mechanical Evaluation of Posterior Wiring as a Supplement to Anterior Cervical Plate Fixation

Rao, Raj D., MD*†; Wang, Mei, PhD*†; Singrakhia, Manoj D., MD*; McGrady, Linda M., BS*†

doi: 10.1097/01.brs.0000142431.63750.80
Cervical Spine
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Study Design. An in vitro experimental study was performed to examine 3-dimensional biomechanical stability of cervical fixations.

Objectives. To determine whether posterior interspinous wiring contributes to the rigidity of a single-level motion segment that has been plated anteriorly, and to determine the effects of this combined fixation on intradiscal pressure and spinal motion at the adjacent segments.

Summary of Background Data. Combined anterior and posterior column fixation is being increasingly used in a variety of clinical situations that do not involve complete disruption of the motion segment. The biomechanical validity of combined anterior posterior fixation in the absence of overt posterior ligamentous disruption has not been studied.

Methods. Six human fresh-frozen cadaveric cervical spines (C3–T1) were used. Three-dimensional intersegmental motion and intradiscal pressure were measured while the spine was loaded in flexion, extension, lateral bending, and torsion (up to 2.5 Nm). Fixation stability at the operative level (C5–C6) and influence of the fixation on adjacent segments were evaluated after an anterior plating procedure and combined anterior plating and posterior wiring.

Results. Comparing the combined approach with anterior plating alone, significant reductions in C5–C6 motion was noted: 49% in flexion (P <0.05), 48% in extension (P <0.003), and 33% and 39%, respectively, in left and right torsion (P <0.05). Reduction in the left and right lateral bending was not significant (18% and 12%, respectively). The improved fixation had minimal influence on the adjacent segments.

Conclusions. Combined anterior posterior fixation further reduces the segmental motion by almost 50% in flexion and extension, 33% and 39% in torsion, and does not significantly alter intradiscal pressure and spinal motion at adjacent segments.

The biomechanical validity of combined anterior posterior fixation in the absence of overt posterior ligamentous disruption has not been studied. This study examines the additional rigidity provided by posterior interspinous wiring to a motion segment that has been plated anteriorly, and to evaluate its effects on intradiscal pressure and spinal motion at the adjacent segments.

From the *Department of Orthopaedic Surgery, Medical College of Wisconsin; and the †Orthopaedic and Rehabilitation Engineering Center, Marquette University, Milwaukee, Wisconsin.

Acknowledgment date: June 16, 2003. First revision date: September 15, 2003. Second revision date: November 6, 2003. Acceptance date: November 17, 2003.

The device(s)/drug(s) is/are FDA-approved or approved by corresponding national agency for this indication.

No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

Address correspondence and reprint requests to Raj D. Rao, MD, Director of Spine Surgery, Medical College of Wisconsin, Department of Orthopaedic Surgery, 9200 W. Wisconsin Ave., PO Box 26099, Milwaukee, WI 53266-0099; E-mail: rrao@mcw.edu

© 2004 Lippincott Williams & Wilkins, Inc.