Objective

Preservation of segmental mobility and the potential to minimize adjacent segment disease have led to cervical disc arthroplasty devices (CDA). The FDA approved cervical devices have different features such as design, type of contact and biomaterials used. The objectives of this study were to determine motions, intradiscal pressures, and facet forces representing the external intervertebral joint-specific kinematics, and the internal anterior and posterior column load sharing of four CDAs. 

Methods

A validated 3D finite element model of the C2-T1 osteoligamentous column was considered for this study. The model consists of (a) cancellous core and cortical shell of the bodies, their posterior elements, i.e., laminae, pedicles and spinous processes, and the dens of the axis, (b) intervertebral disc annular fibers, ground substance, and nucleus pulposus, and (c) anterior and posterior longitudinal ligaments, joint capsules of the lateral mass, ligamentum flavum, and interspinous ligaments. The boundary conditions are such that T1 vertebrae are fixed and a moment is applied at the superior of C2 vertebrae. This column is subjected to physiological flexion-extension, and the overall and segmental angular motions from C2-C3 to C7-T1 were obtained. CDA is instrumented in the intact model at the C5-C6 level as per clinical procedure by removing the Intervertebral disc, posterior longitudinal ligament, and anterior longitudinal ligament.  The hybrid loading protocol applied moments for the metal on polymer Secure-C, Prodisc-C, and Mobi-C, and metal on metal Prestige LP. All CDA spines were subjected to the moments that produced the same overall range of motion of the intact spine under a pure moment of 2 Nm, representing the physiological loads.  Normalized motions with respect to intact at the index and adjacent segments, and intradiscal pressures and facet column loads were obtained for each CDA. 

Results

While all CDAs restored motion at the index level, differences existed between CDAs regarding the facet column load-sharing. The instrumented level and adjacent segment kinematics for all the CDAs has more changes in extension. The greatest increase occurs in Secure C (48%) and least in Prestige LP (26.5%). The moment required for Secure C in hybrid loading is lesser compared to other CDAs. At the adjacent segments, all the CDAs reduced the range of motion. In addition, both intradiscal pressures and facet column load-sharing depended on the type of the CDA. The metal on metal design (Prestige LP) responded with increasing intradiscal pressure at the adjacent levels whereas other CDAs decreased. The facet load at the adjacent segments reduced in all CDAs and recorded maximum in Mobi C (3.2 times of intact) at the instrumented level. 

Conclusions

The metal on metal disc is different from the metal on polymer designs, and factors such as the allowance of anteroposterior translation are attributed for these differences. Consideration of facet joint integrity should be a factor in the clinical decision-making process for the selection of the CDA.


Biomechanical Study of Cervical Disc Arthroplasty Devices Using Finite Element Models

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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