Failure Mechanism of Posterior Spinal Instrumentation － A Retrieval Study

In order to understand the failure mechanism of posterior spinal implants in vivo, a retrieval analysis of the failed implants was made and metallographic analysis was applied to investigate the broken surfaces of the failed implants to identify the failure modes. The results of metallographic analysis at the broken surfaces of the failed transpedicle screws revealed beach mark sign and striation under scanning electron microscope. In fractography, these signs implied that the screws were broken due to fatigue failure under cyclic axial loading, which was caused by the repeated flexionextension eximplied that the screws were broken due to fatigue failure under cyclic axial loading, which was caused by the repeated flexionextension exercise during trunk motion. Besides, in the three failure cases we collected, non-union of the bone graft was noted in two cases. In conclusion, the failure mechanism of the posterior spinal instrumentation was due to fatigue caused by cyclic axial loading during trunk motion. The result was compatible with the previous in vitro cadaver or animal studies. Besides, we suggested that necessary protection should be addressed to the patients receiving posterior spinal instrumentation, especially in patients with poor compliance and high activity demands.

並列關鍵字

Spinal implant ； Failure mechanism ； Fractography fatigue ； Protection

國際替代計量

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