PhD Dissertation

Abstract

Low back pain can originate from the facet joint, which is innervated by the medial branch of the dorsal rami in the lumbar spine. One of the modalities used to treat facet joint pain is the use of radiofrequency ablation (RFA) of the medial nerve. Since this nerve supplies both facet joints and multifidus muscles, applying RFA will not only alleviate facet joint pain but also adversely affect the multifidus muscle. The multifidus muscle has an essential role in maintaining spinal stability. Activation of the multifidus muscle during different movements affects the pressure within the lumbar intervertebral discs. Therefore, its function is interrelated with the biomechanics of the spine. Denervation after RFA can significantly alter the normal mechanics of the spine, which in turn can lead to or worsen degeneration in spinal tissues such as the intervertebral disc and surrounding ligaments. The goal of this study is to evaluate the impact of the RFA procedure on the biomechanics of the spine. To achieve this, first, force-dependent kinematics simulations of different torso movements were performed to quantify the changes in joint forces and vertebral rotations that occur after denervation of the multifidus. These changes were found to be significant, especially after bilateral ablation compared to unilateral ablation. These results were used to evaluate changes in stresses and strains in soft tissues of the spine. To create an anatomical representation of the spine for both female and male populations, statistical shape models of the vertebrae were developed from a collection of computed tomography images. Finally, a finite element model was developed and validated using the statistical shape models and the forces and angular changes from the force-dependent kinematics model. The finite element analysis (FEA) showed that RFA alters the stress distribution in the intervertebral disc, increasing the risk of disc degeneration. This approach may elucidate the effect of RFA on the intervertebral disc.