Augmentation of an anterior lumbar interbody fusion with an anterior plate or pedicle screw fixation: a comparative biomechanical in vitro study

Abstract

<jats:sec> <jats:title>Object</jats:title> <jats:p>Posterior pedicle screw (PS) instrumentation is often used to augment anterior lumbar interbody fusion (ALIF) but at the cost of an increase in the morbidity rate due to the second approach and screw placement. If anterior plates were found to be biomechanically equivalent to PS fixation (PSF) after ALIF, then this second approach could be avoided without decreasing vertebral stability.</jats:p></jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>Eight cadaveric L5–S1 spinal segments were tested under four conditions: intact, following anterior discectomy and interbody spacer placement, after placement of an anterior plate, and following PSF. The elastic zone and stiffness were calculated for axial compression, flexion/extension, lateral bending, and torsion.</jats:p> <jats:p>Neither anterior plate stabilization nor PSF showed significant intergroup differences in stiffness or the elastic zone. Both exhibited greater stiffness in flexion than the intact specimens (p &lt; 0.001). Pedicle screw fixation was associated with a decreased elastic zone in lateral bending compared with the intact specimen (p &lt; 0.04).</jats:p></jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>Anterior plate fixation is biomechanically similar to PSF following ALIF. Surgeons may wish to use anterior plates in place of PSs to avoid the need for a posterior procedure. This may lead to a decrease in operative morbidity and improved overall outcomes.</jats:p></jats:sec>

Craniocervical Fixation With Occipital Condyle Screws

“…All tests were performed with specimens mounted in a MTS Mini Bionix 858 servo hydraulic testing machine (MTS Systems Corp., Eden Prairie, MN) modified with the addition of a custom 2-degree-of freedom spine testing fixture as previously described. 25 The occiput was secured in a custom potting frame at one end and C-3 at the other.…”

“…Specimens were stored at Ϫ20°C and thawed overnight at 25°C, before testing. 25 Specimens were dissected in the Osman Microsurgery Laboratory and biomechanical testing performed in the Spine Biomechanics Laboratory, Department of Neurosurgery, University of South Florida. After thawing, specimens were dissected free of all extraneous muscle and soft tissues, leaving the ligaments, joints, and osseous structures intact.…”

Pullout of a lumbar plate with varying screw lengths

“…25 Other means of stabilization include the addition of posterior instrumentation, such as pediclebased fusion devices and interspinous spacers. 3,4,26 The limitations of this study are similar to those of many in vitro biomechanical studies. First, construct failure through pullout differs from in vivo construct failure, which involves cyclic loading mechanisms.…”

“…Numerous biomechanical studies have shown the stabilizing efficacy of anterior plates to approximate that of posterior fixation. 3,4 When stability supplementation comes from an anterior plate, the holding power of screws securing the anterior plate in place relates to procedural success. Many authors have studied factors pertaining to screw stability, such as bone density, outer screw diameter, outer screw diameter-to-inner screw diameter ratio, thread pitch, cannulation, and screw length.…”

Screw Orientation and Foam Density Interaction in Pullout of Anterior Lumbar Interbody Fusion Plates

“…4 Although pedicle screw fixation has been shown to provide greater biomechanical stability in lateral bending, anterior plates have been shown to provide sufficient immobilization for fusion while obviating intraoperative repositioning of the patient and a second approach. [5][6][7] Anterior plate fixation in ALIF procedures has become increasingly popular over the last 7 years. 8 While the stability of lateral plates and posterior fixation has been previously studied, research regarding the stability of straight anterior plates remains relatively scarce.…”