[Artificial Disc Replacement] Study of Spine Motion After M6 Cervical Implant

[Researcher]

I came across this paper just published in the European Spine Journal (September 24, 2010). It was interesting other than the fact that 12 cadaver spines were used.

Phil

SpringerLink - European Spine Journal, Online First

Primary and coupled motions after cervical total disc replacement using a compressible six-degree-of-freedom prosthesis

A. G. Patwardhan, M. N. Tzermiadianos, P. P. Tsitsopoulos, L. I. Voronov, S. M. Renner, M. L. Reo, G. Carandang, K. Ritter-Lang and R. M. Havey

Abstract

This study tested the hypotheses that (1) cervical total disc replacement with a compressible, six-degree-of-freedom prosthesis would allow restoration of physiologic range and quality of motion, and (2) the kinematic response would not be adversely affected by variability in prosthesis position in the sagittal plane. Twelve human cadaveric cervical spines were tested.

Prostheses were implanted at C5–C6. Range of motion (ROM) was measured in flexion–extension, lateral bending, and axial rotation under ±1.5 Nm moments. Motion coupling between axial rotation and lateral bending was calculated. Stiffness in the high flexibility zone was evaluated in all three testing modes, while the center of rotation (COR) was calculated using digital video fluoroscopic images in flexion–extension.

Implantation in the middle position increased ROM in flexion–extension from 13.5 ± 2.3 to 15.7 ± 3.0° (p < 0.05), decreased axial rotation from 9.9 ± 1.7 to 8.3 ± 1.6° (p < 0.05), and decreased lateral bending from 8.0 ± 2.1 to 4.5 ± 1.1° (p < 0.05). Coupled lateral bending decreased from 0.62 ± 0.16 to 0.39 ± 0.15° for each degree of axial rotation (p < 0.05). Flexion–extension stiffness of the reconstructed segment with the prosthesis in the middle position did not deviate significantly from intact controls, whereas the lateral bending and axial rotation stiffness values were significantly larger than intact. Implanting the prosthesis in the posterior position as compared to the middle position did not significantly affect the ROM, motion coupling, or stiffness of the reconstructed segment; however, the COR location better approximated intact controls with the prosthesis midline located within ±1 mm of the disc-space midline.

Overall, the kinematic response after reconstruction with the compressible, six-degree-of-freedom prosthesis within ±1 mm of the disc-space midline approximated the intact response in flexion–extension. Clinical studies are needed to understand and interpret the effects of limited restoration of lateral bending and axial rotation motions and motion coupling on clinical outcome.

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[trkdoc714]

Phil,

It is interesting. None of the recipients complained of any radicular pain after the procedure. I guess that's just good patient selection.

Seriously though, great article. I came across similar articles while researching the Maverick disc. Cadaver testing can give good feedback when designing devices. This helps making adjustments to design or technique before a live patient is implanted.

I wonder if that type of job has a dental plan........

[Researcher]

Great sense of humor trkdoc714. Maybe I should add my spine to my organ donors list. I'm also glad that they were able to learn more about the effect of disc position on spinal motion. I'm looking forward to the day when my failing discs have been replaced with ones that work more like new OEM discs. I'm just one insurance company and about $50k away from success.

Phil