SPINE Volume 34, Number 1, pp E9 –E15 ©2008, Lippincott Williams & Wilkins Anterior Cervical Discectomy and Fusion With a Locked Plate and Wedged Graft Effectively Stabilizes Flexion-Distraction Stage-3 Injury in the Lower Cervical Spine A Biomechanical Study Odysseas Paxinos, MD,*† Alexander J. Ghanayem, MD,* Michael R. Zindrick, MD,*‡ Leonard I. Voronov, MD, PhD,*† Robert M. Havey, BS,*† Gerard Carandang, MS,† Alexander Hadjipavlou, MD,§ and Avinash G. Patwardhan, PhD*† Study Design. An in vitro three-dimensional (3D) flex- ibility test of human C3–C7 cervical spine specimens. Objective. To test the hypothesis that anterior cervical fusion with a wedged graft and a locked plate can effec- tively stabilize the cervical spine after complete anterior and posterior segmental ligamentous release. Summary of Background Data. Distraction-flexion Stage 3 injuries of the lower cervical spine (bilateral facet dislocations) are usually reduced under awake cranial traction. When the magnetic resonance imaging reveals a traumatic disc prolapse, anterior cervical discectomy and fusion (ACDF) is usually recommended. Most authors ad- vise combining ACDF with posterior instrumentation to address the insufficiency of the posterior elements. How- ever, there is clinical evidence that ACDF with a locked plate alone suffices for the treatment of these injuries, especially in young patients. Still, there are no biome- chanical studies on the effect of a locked plate on the complete anterior and posterior ligamentous-deficient young cervical spine under physiologic preload. Methods. Eight fresh frozen human lower cervical spines (C3–C7) from young donors (age, 44.5 years; range, 21– 63 years) were used. A 3D flexibility test was conducted using a moment of 0.8 Nm without preload. Flexion-extension was additionally tested using a mo- ment of 1.5 Nm under 0 and 150 N follower preload. Spines were tested first intact, then after complete C5–C6 discectomy with posterior longitudinal ligament resection and ACDF with a wedged bone graft and a rigid locked plate, and finally after complete release of the supraspi- nous, interspinous, and intertransverse ligaments; the facet capsules; and ligamentum flavum. Results. When tested under 0.8 Nm moment without preload, complete posterior and anterior ligamentous re- lease did not significantly increase the ROM of the ACDF construct in flexion-extension (P  0.025), lateral bending (P  0.025), and axial rotation (P  0.025). When tested under 1.5 Nm moment with or without a compressive pre- load, the complete posterior and anterior ligamentous re- lease did not significantly affect the ROM of the ACDF con- struct (P  0.01). The application of preload significantly reduced the motion at the C5–C6 ACDF construct with liga- mentous disruption in comparison with the motion in the absence of a preload (P  0.01). Conclusion. Anterior cervical fusion with a wedged graft and a rigid constrained (locked) plate can effectively stabilize the nonosteoporotic cervical spine after com- plete posterior element injury when excessive ROM is prevented (for example, by the use of postoperative ex- ternal immobilization). Even when the construct is sub- jected to higher moments, adequate stability can be achieved when physiologic preload is present. Osteopo- rosis and lack of sufficient preload due to poor neuromus- cular control may affect long-term screw stability, and additional external immobilization may be needed until fusion matures. Key words: cervical spine, flexion-distraction injury, trauma, facet dislocation, ACDF, preload, follower load. Spine 2009;34:E9 –E15 Distraction-flexion (DF) injuries are usually the result of motor vehicle accidents and account for about 10% of all injuries to the lower cervical spine. Allen et al have classified these injuries in 4 stages, with distraction-flexion Stage 3 (DFS-3) representing bilateral facet dislocation with ap- proximately 50% anterior subluxation of the upper verte- bral body in the motion segment. 1 In the past, several au- thors have reported good results in treating these injuries with posterior instrumentation, using either wires 2–4 or plates, 5–7 and many biomechanical studies over the years have shown posterior instrumentation provides better ini- tial stability than anterior fixation alone. 8 –13 Recently, several authors have reported very good fu- sion rates and clinical results in treating these highly un- stable injuries with 1-stage anterior cervical discectomy and fusion (ACDF) with bone graft and an anterior lock- ing plate. 14 –17 Clinical failures of DFS-3 injuries treated in this manner have been linked to poor cervical neuro- muscular control due to complete paralysis, 14 suggesting From the *Department of Orthopaedic Surgery and Rehabilitation, Loyola University Medical Center, Maywood; †Edward Hines Jr. VA Hospital, Hines; ‡Hinsdale Orthopaedic Associates, Hinsdale IL; and §University of Crete, Heraklion, Greece. Acknowledgment date: July 23, 2007. First revision date: March 7, 2008. Second revision date: July 9, 2008. Acceptance date: July 14, 2008. Supported by institutional grants provided by the Department of Vet- erans Affairs, WA, DC, and Hinsdale Spine Foundation, Hinsdale, IL. The device(s)/drug(s) is/are FDA-approved or approved by correspond- ing national agency for this indication. Institutional funds (Department of Veterans Affairs) funds were re- ceived 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 Avinash G. Pat- wardhan, PhD, Department of Orthopaedic Surgery and Rehabilita- tion, Loyola University Medical Center, 2160 S. First Avenue, May- wood, IL 60153; E-mail: apatwar@lumc.edu E9