Biomechanical Study of Posterior Lumbar Interbody Fusion
Date Issued
2015
Date
2015
Author(s)
Chou, Wen-Kai
Abstract
Posterior Lumbar Interbody Fusion (PLIF) is one of the most common surgical techniques employed to treat spinal deformity, degeneration and other instability related conditions. With the improved understanding of the spine biomechanics combined with the advancement of medical devices as well as the heightened expectations of the general public in pursuing better health and quality of life, the demand for PLIF is ever increasing in the modern society. Despite its well-published effectiveness in relieving clinical symptoms, the frequent development of secondary complications requiring revision surgery associated with PLIF inevitably reduces its clinical efficacy. It is therefore the primary aim of the current project to investigate the mechanisms underlying the development of secondary complications associated with PLIF through a series of in-vitro studies using both porcine and human cadaver specimens. The secondary aim of the project focused on the issues of implant failure and the development of adjacent segment disease after instrumentation and more importantly, discussed some plausible design modifications for future implant development. The first study of the project was an in-vitro cadaveric study designed to determine the exact role of the pedicular cortical bone composition and the screw-bone gap on the screw fixation failure. The results of the study identified a significant correlation between cortical bone area ratio and the screw pullout strength. Presented results also demonstrated that the fatigue loading induced screw-bone gap of 1 mm was sufficient to cause a significant decrease in the pullout strength. However, a cortical bone area ratio of 0.73 or higher in this group was able to preserve most of the screw-bone interfacial strength and subsequently may play an important role in preventing a complete implant failure in clinical practice. The second study in the series was an in-vitro fatigue-loading test utilizing porcine specimens to comparatively analyze the biomechanical performance of PEEK and Titanium rods construct subjected to a battery of fatigue loading testing. Based on the results, it was determined that the differences in biomechanical characteristics of PEEK and Titanium rods construct when subjected to fatigue loading. More specifically, the result is indicative of the potential benefits of the PEEK rods construct in reducing the risks of adjacent segment disease and implant failure rates. The final study in this series investigated the effect of altered mobility of the instrumented level and its consequential impact on the biomechanical characteristics of the adjacent segment levels. The outcome of the study demonstrated that the increasing range of motion at the instrumented level is associated with decreased compensatory motion and intra-discal pressure at the adjacent segments. It was also determined that a maximum of 4.04° into flexion and 2.41° into extension achieved maximum stability of the instrumented level coupled with minimal biomechanical compensatory at the adjacent levels. Such finding is of significant clinical value as it provides a guideline for the future design and development of more advanced spinal implants. Overall, the series of studies comprised in the current project investigated the possible mechanisms associated with the development of secondary complications post PLIF surgery and proposed plausible solutions to overcome each of the shortcomings by identifying more appropriate medical material or through modification of device design. The outcomes of the project provided valuable knowledge base and guidelines for clinicians performing PLIF and it is hoped that the presented information will ultimately assist in the reduction of secondary complications and revision surgery associated with PLIF and subsequently improve the long-term quality of life for the patients.
Subjects
Posterior lumbar interbody fusion
Biomechanics
Implant failure
Adjacent segment disease
SDGs
Type
thesis
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