Session: 07-07-02: Computational Modeling in Biomedical Applications II

Paper Number: 165763

Dynamic Responses of Cervical Spine Artificial Discs 

Introduction: Spinal disorders such as neck pain is known to be associated with degeneration that occurs with the ageing process.  They are also common in the younger populations such as athletes and military personnel.  These younger groups subject the spine to more frequent dynamic loading than others.  In either case, treatment options remain the same, however.  The classic surgical treatment is Anterior Cervical Discectomy and Fusion (ACDF) that involves removing the affected disc and replacing it with bone graft and plates connecting the two vertebral bodies. This procedure essentially renders the intervertebral joint rigid at this level, and transfers any motion to the adjacent segments, i.e., superior and inferior disc and facet joints.  A common negative effect of ACDF is that the adjacent segments degenerate quickly over time and may need further clinical attention, including surgery for those disc(s).  Preserving some motion at the affected disc level transfers less motion to the adjacent segments, and this is the fundamental concept in cervical spine artificial disc. The surgical procedure often termed as Cervical Total Disc Replacement (CTDR). While many artificial disc replacements are available and approved by the FDA, almost all studies are focused on quasi-static/physiological loading encountered in a majority of civilians.  This study aims to evaluate the biomechanical response of a CTDR device under dynamic loading for certain occupational scenarios (military pilots) and compare its effects with those observed under quasi-static/physiological loading.

Methods: Global Human Body Models Consortium’s mid-size male occupant was used. The intact model was validated under dynamic loading using human cadaver test data.  The model with helmet was seated upright in a seat with a harness system, and a vertical acceleration pulse was applied.  A single-level CTDR was simulated at C5-C6 segment. The three-component of the CTDR design was unconstrained and had a metal-polymer-metal articulation. Key biomechanical parameters including range of motion, disc pressure, and facet loads were assessed at the CTDR level (C5-C6) and at adjacent levels (C4-C5 and C6-C7). The responses were normalized to those of an intact spine under identical loading conditions.

Results: Briefly, at the CTDR level (C5-C6), the range of motion decreased by 31% under dynamic loading and increased by 37% under physiological loading. At the superior level (C4-C5), motion decreased in both loading cases: 3% under dynamic and 10% under physiological loading. At the inferior level (C6-C7), motion increased by 13% under dynamic loading and decreased by 11% under physiological loading.

Conclusion: The chosen CTDR design preserved motion at the CTDR level under dynamic loading. However, the increase in motion was less than the increase observed under quasi-static loading. While the trends are similar, the effectiveness of the artificial disc appears to be somewhat reduced under dynamic loading. Adjacent level motion was lower with the CTDR. Further analysis of disc pressures and facet loads, representing anterior and posterior column load sharing, will be discussed. The inferior level sustaining more motion than the superior level suggests a greater susceptibility of the inferior segment to degeneration.

Presenting Author: Balaji Harinathan Medical College of Wisconsin

Presenting Author Biography: Balaji Harinathan is a Ph.D. candidate specializing in biomechanics, solid mechanics, and finite element analysis.

Authors:

Balaji Harinathan Medical College of Wisconsin
Hoon Choi Cleveland clinic, Weston, FL
Narayan Yoganandan Medical College of Wisconsin