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A New Stand-Alone Anterior Lumbar Interbody Fusion Device: Biomechanical Comparison with Established Fixation Techniques

Cain, Christopher M. J. MD*; Schleicher, Philip MD; Gerlach, Rene; Pflugmacher, Robert MD; Scholz, Matti MD; Kandziora, Frank MD, PhD

doi: 10.1097/01.brs.0000187897.25889.54
Basic Science

Study Design. Established lumbar fixation methods were assessed biomechanically, and a comparison was made with a new stand-alone anterior lumbar interbody cage device incorporating integrated anterior fixation.

Objectives. To compare the stability of a new stand-alone anterior implant (Test-device) with established fixation methods to assess its suitability for clinical use. Our hypothesis being that the Test-device would provide stability comparable to that provided by an anterior cage when supplemented with posterior pedicle screw fixation.

Summary of Background Data. It is accepted that the use of rigid pedicle screw instrumentation increases the chance of achieving a solid fusion, but its use may be associated with a significant increase in postoperative morbidity caused by disruption of the posterior musculature. It is also evident that this increased fusion rate is generally not associated with increased clinical success. This dilemma has led to a search for a solution and to the development of the Test-device anterior lumbar interbody device.

Methods. The kinematic properties of either the L3–L4 or L4–L5 lumbar motion segment of 8 cadaveric lumbar spines have been tested using the following sequence of fixation: intact, Test-device, Test-device and translaminar facet screws (TS), Cage and TS, Cage and Universal Spine System (USS), and Cage and small stature USS.

Results. All fixation techniques except the cage and TS decreased (P < 0.05) range of motion (ROM), neutral zone (NZ), and elastic zone (EZ), and increased (P < 0.05) stiffness in comparison to the intact motion segment in all test modes. There was a significant increase (P < 0.01) in the ROM, NZ, and EZ, and decrease in the stiffness of the cage and TS group in comparison to all other stabilizationtechniques in flexion and rotation. There was no significant difference in the ROM, NZ, EZ, and stiffness between the Test-device and cage and USS groups in flexion, extension, and bending. The Test-device resulted in a significantly lower EZ (P < 0.05) and a significantly higher stiffness (P < 0.05) in rotation than all other fixation methods.

Conclusions. The Test-device alone provided similar and the Test-device and TS higher stability than the pedicle screw constructs evaluated. These results support progression to clinical trials using the Test-device as a stand-alone implant.

This study evaluates the stability provided by a new stand-alone anterior fusion device and compares its biomechanical stability with established fusion constructs. The stability provided by this implant was comparable to that of pedicle screw fixation in flexion, extension, and lateral bending, and was superior in axial rotation.

From the *Adelaide Spine Clinic, Adelaide, Australia, and †Unfall-und Wiederherstellungschirurgie, Universitätsklinikum Charité der Humboldt Universität Berlin, Berlin, Germany.

Acknowledgment date: September 21, 2004. First revision date: February 7, 2005. Second revision date: March 1, 2005. Acceptance date: March 7, 2005.

Mathys (Bettlach, Switzerland) provided the implants and instrumentation systems used, and financially supported the preparation, evaluation, and completion of this work. We acknowledge the commercial interest Mathys (now Synthes) has in the development of this device.

The device(s)/drug(s) that is/are the subject of this manuscript is/are not FDA- approved for this indication and is/are not commercially available in the United States.

Corporate/Industry funds were received in support of this work. One or more of the author(s) has/have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this manuscript: honoraria, gifts, consultancies.

Address correspondence and reprint requests to Christopher M. J. Cain, MD, Adelaide Spine Clinic, 252 East Terrace, Adelaide SA 5000, Australia; E-mail: drcmjcain@adelaide.on.net, www.spine.com.au

© 2005 Lippincott Williams & Wilkins, Inc.