The Journal of Bone and Joint Surgery (American). 2006;88:1566-1573.
doi:10.2106/JBJS.E.00305
© 2006 The Journal of Bone and Joint Surgery, Inc.
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Anterior Cervical Fixation: Analysis of Load-Sharing and Stability with Use of Static and Dynamic Plates

Darrel S. Brodke, MD1, Paul Klimo, Jr., MD, MPH2, Kent N. Bachus, PhD1, John T. Braun, MD1 and Andrew T. Dailey, MD3

1 Department of Orthopaedics (D.S.B., K.N.B., and J.T.B.) and Orthopaedic Research Laboratory (K.N.B.), University of Utah Orthopaedic Center, 590 Wakara Way, Room A0100, Salt Lake City, UT 84108. E-mail address for K.N. Bachus: kent.bachus{at}hsc.utah.edu
2 Department of Neurosurgery, University of Utah School of Medicine, 30N 1900E, Suite 3B409 SOM, Salt Lake City, UT 84132
3 Rocky Mountain Neurosurgical Alliance, 701 E Hampden Avenue #510, Englewood, CO 80110

Investigation performed at the Department of Orthopaedics and the Orthopaedic Research Laboratory, University of Utah Orthopaedic Center, Salt Lake City, Utah

In support of their research for or preparation of this manuscript, one or more of the authors received grants or outside funding from Medtronic. None of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. A commercial entity (Medtronic) paid or directed, or agreed to pay or direct, benefits to a research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Background: Anterior plates provide stability following decompression and fusion of the cervical spine. Various plate designs have emerged, and they include static plates with fixed-angle screws, rotationally dynamic plates that allow the screws to toggle in the plate, and translationally dynamic plates that allow the screws to both toggle and translate vertically. The goal of this study was to document the effects of plate design following a single-level corpectomy and placement of a full-length strut graft and the effects following 10% subsidence of the graft.

Methods: A total of twenty-one cadaveric cervical spines (C2-T1) were randomized into three treatment groups and were tested for initial range of motion. A C5 corpectomy was performed, reconstruction was done with a full-length interbody spacer containing a load-cell, and an anterior cervical plate was applied. Load-sharing data were recorded with incremental axial loads. The range of motion was measured with ±2.5 Nm of torque in flexion-extension, lateral bending, and axial rotation. Then, the total length of the interbody spacer was reduced by 10% to simulate subsidence, and load-sharing and the range of motion were retested.

Results: With the full-length interbody spacer, there were no significant differences in the abilities of the constructs to share load or limit motion. Following shortening of the interbody spacer, the static plate construct lost nearly 70% of its load-sharing capability, while neither of the dynamic plate constructs lost load-sharing capabilities. Also, the static plate construct allowed significantly more motion in flexion-extension following simulated subsidence than did either of the dynamic plate constructs (p < 0.05).

Conclusions: Although all of the tested anterior cervical plating systems provide similar load-sharing and stiffness following initial placement of the interbody spacer, the static plate system lost its ability to share load and limit motion following simulated subsidence of the interbody spacer. Both dynamic plate systems maintained load-sharing and stiffness despite simulated subsidence.

Clinical Relevance: This study provides an improved understanding of the immediate performance of anterior cervical fusion surgery with plate fixation.


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