Biomechanical Evaluation of Spinal Fixation Devices

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Abstract
The three-dimentional stability provided by six spinal fixation devices with or without interbody bone graft has been studied in an in vitro biomechanical model using five-vertebral (T11-L3) fresh cadaveric thoracolumbar specimens. An injury was created at T12-L1 by complete transection of the posterior elements and posterior half of the intervertebral disc, leaving the anterior half of the intervertebral disc and anterior longitudinal ligament intact. The three-dimensional rotations and translations, measures of biomechanical instabilities, were determined under physiologic loads for the intact spine and the spinal constructs, ie, injured spine plus instrumentation. The tested devices were: Harrington reverse ratchet rods (HR); Luque rectangle rod (LR); Kaneda device without transverse fixator (KD); Kaneda device with transverse fixators (KT); transpedicular external fixator (EF). In addition, stability tests were performed for KT, EF, and Harrington compression rods with interbody bone graft following a corpectomy (KTB, EFB, and HCB). The constructs were more stable than the intact spine under the four loads in the following order: flexion: EFB, HCB, EF, HR, LR, KTB, and KT; extension: EFB, LR, EF, KTB, HR, and KT; lateral bending: KTB, KT, EFB, KD, EF, HCB, and HR; and axial rotation: EFB.

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