Biomechanical effects of the body augmenter for reconstruction of the vertebral body.
METHODS
An in vitro biomechanical study of the stabilizing effects of the body augmenter and posterior instrumentation on experimental thoracolumbar fractures with vertebral defects.


OBJECTIVE
To evaluate the effects of the body augmenter and instrumentation on the stability of the spine-device construct.


BACKGROUND
Posterior instrumentations alone are widely used to accomplish spinal reduction and provide stability for an injured spine; however, implant failure rates have been reported to be approximately 20%. Transpedicular discectomy and bone graft has reported only 33% fusion rates. Combined anterior bony strut and posterior instrumentation was a challenge to geriatric patients with vulnerable medical conditions and possible vascular and pulmonary complications. Therefore, a new design, the body augmenter, tries to reconstruct the vertebral body through internal mechanical support and also encourage bony fusion. This study is to evaluate its initial mechanical effects.


METHODS
Twenty fresh porcine T11-L3 vertebrae were harvested. The L1 vertebra with one third or one half corpectomy was performed to simulate a fracture injury with vertebral defects. Posterior instrumentation alone (PI group), posterior instrumentation with body augmenters (BA group), and anterior instrumentation with tricortical bony strut and DCP 1 level above and 1 level below the fracture site (DCP group) were applied as treatment strategies. Load-displacement and torque-angle plots were generated and used to calculate axial stiffness and torsional rigidity for these constructs with vertebral fracture at the L1 vertebrae. Axial compression, extension, and flexion tests were performed at intact and spine-device constructs to document spinal stability.


RESULTS
The construct stability had a complex association to the device applied. In the one third corpectomy group, the BA group had significantly higher compression stiffness than the PI group. In the one half corpectomy group, the flexion and compression stiffness of the BA group became significantly greater than the PI group, and the extension stiffness is significantly higher than the DCP group.


CONCLUSIONS
The body augmenters combined with posterior instrumentation increased the spinal construct stability during compression, flexion, and extension. According to results in this study, the body augmenter could provide a better initial stability of construct and prevent the implant failure of posterior instrumentation and may be a feasible substitute for the anterior role in the future.
Chen
Hsiang-Ho
HH
I-Shou University, Department of Biomedical Engineering, Chia-Yi Yang-Ming Hospital, Taiwan, ROC.
Wang
Wei-Kai
WK
Li
Kung-Chia
KC
Chen
Tain-Hsiung
TH
D000818:Animals; D001696:Biomechanical Phenomena; D005593:Fracture Fixation, Internal / Q000295:instrumentation; D020007:Implants, Experimental; D016268:Internal Fixators; D008159:Lumbar Vertebrae / Q000293:injuries / Q000601:surgery; D016103:Spinal Fractures / Q000601:surgery*; D034421:Sus scrofa; D013904:Thoracic Vertebrae / Q000293:injuries / Q000601:surgery