Experimental discovery of surgical guidelines for cervical disc augmentation

University of Minnesota Ph.D. dissertation. May 2012. Major: Biomedical Engineering. Advisor: Professor David J. Nuckley. 1 computer file (PDF); vii, 181 pages, appendices A-C.Intervertebral disc degeneration of the cervical spine affects over one half of all individuals over the age of 40 years and the last decade has seen an alarming increase in cervical disc degenerative disease related surgeries. In spite of newer technological advancements in devices for disc degeneration disease, spinal disc replacement and fusion, revision surgery rates have remained unchanged. 90% of the disc replacement revisions and 50% of fusion related revision can be attributed to improper device selection. Therefore, the objective of this research is to evaluate disc arthroplasty (replacement) and arthrodesis (fusion) devices and identify optimal implant size (height) selection criteria for biomechanical competence in force transmission, motion, and neurologic tissue protection. Eleven osteo-ligamentous human cadaver cervical spines were biomechanically evaluated after surgical augmentation with different sized implants for both arthroplasty and arthrodesis. The biomechanical outcomes measured were range of motion, neutral zone, stiffness, articular pillar strains, facet forces and intervertebral foramen area. Increased disc distraction was found to increase lordosis of the spine, increase compressive strains in articular pillars and increase in intervertebral foramen area. The kinematics outcomes were surgery type and implant size dependent where fusion lead to decreased range of motion, while arthroplasty maintained the range of motion with differential outcomes based upon the size of the implant. The integration of these biomechanical data demonstrate an implant size /spacer height relationship with direct clinical importance and the ability to guide clinical decision making so as to reduce revision surgery due to deviant biomechanical function