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Mechanical Engineering
BYU Applied Biomechanics Engineering Laboratory

Motion Preservation Devices

Compliant Mechanisms as Spinal Motion Restoration Systems

Spinal fusion is a surgical technique in which two or more vertebrae of the spine are united together via bone grafts and spinal instrumentation. The goal of spinal fusion is to encourage bone growth between the vertebrae such that mechanically the two vertebrae move as one, removing motion at the degenerated segment. Spinal fusion is not universally effective, and a recent study reported patient satisfaction rates with the procedure at 53%. Despite mediocre patient satisfaction rates with lumbar spinal fusion, demand is projected to grow by 2200% from 2005 to 2030. Our current understanding of the mechanical repercussions of spinal fusion on adjacent levels is not yet fully developed. There is some evidence that degenerative changes in intervertebral discs at levels adjacent to spinal fusion may simply be the result of natural aging processes. Recent studies however, have indicated that adjacent level intervertebral disc degeneration is accelerated following fusion surgery.

As an alternative to fusion, there has been significant effort expended over the last decade towards development of motion preservation and motion restoration devices for the spine. The first generation versions of these motion restoration devices (MRDs) have entered the US market over the last five years, and the short term results for these devices have been encouraging. However, the biomechanical characteristics of these devices are significantly different from those of intact spinal motions segments, and there are substantial questions regarding the medium- and long-term biomechanical response of the surrounding host environment following surgical treatment with these devices.

Compliant mechanisms have properties that make them uniquely suited for motion restoration devices: they gain their motion from the deflection of flexible members rather than from traditional articulated components, they are compact, high precision devices that are capable of sophisticated force-displacement profiles, and they generate little or no wear. The spinal disc itself is a compliant mechanism. This and other highly evolved compliant systems in nature are complex but compact and efficient, and compliant mechanism theory allows these properties to be accessible to man-made systems.

Working in collaboration with the BYU Compliant Mechanisms Research group (http://research.et.byu.edu/llhwww), we have developed two motion restoration devices with pending patents that have been licensed by Crocker Spinal Technologies. For more information on these products, please see their website (http://www.crockerspinaltechnologies.com).

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The FlexBAC™ lumbar total disc replacement.
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The FlexBAC™ lumbar total disc replacement.
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The FlexSuRe™ posterior dynamic motion restoration system.
FlexSuRe.jpg
The FlexSuRe™ posterior dynamic motion restoration system.

Related Publications


Shkolnikov, Y.P., Bowden, A.E., MacDonald, D., Kurtz, S.M. (2010). "Wear pattern observations from TDR retrievals using autoregistration of voxel data." J Biomedical Materials Research Part B: Applied Biomaterials Early View, Published online May 24, 2010.

Stratton, E., Howell, L.L., and Bowden, A. (2010). “Force-displacement Model of the FlexSuReTM Spinal Implant.” Proceedings of the ASME International Design Engineering Technical Conferences, Montreal, Quebec, Aug 15-18, 2010, DETC2010- 28476.

Bowden, A.E., H.L. Guerin, M.L. Villarraga, A.G. Patwardhan, and J.A. Ochoa (2008). “Quality of motion considerations in numerical analysis of motion restoring implants of the spine.” Clinical Biomechanics 23(5):536-544.

Halverson, P.A., L.L. Howell, and A.E. Bowden (2008). “A flexure-based bi-axial contact-aided compliant mechanism for spinal arthroplasty,” DETC2008-50121.

Mazzucco, D., A. E. Bowden and K. L. Ong (2006). "Examining failure causation in retrieved implant devices." Medical Device & Diagnostic Industry(Jan): 110-115.

Coleman, J.C., A.E. Bowden, S. Rundell, R.P. Nockels, and K.T. Foley (2008). Effect of semi-rigid posterior rods on kinematic stability and load distribution in the lumbar spine. Proc AANS/CNS, Chicago, IL, April 26-May 1.

Halverson, P., A.E. Bowden and L.L. Howell (2008). Wearless total disc arthroplasty through compliant mechanism design. Spine Arthroplasty Summit 8, Miami, FL, May 6-9.

Bowden, A.E., H.L. Guerin, M.L. Villarrage, A.G. Patwardhan, and J.A. Ochoa (2008). Higher order validation metrics are required when numerically modeling physiologic motion of the spine. Trans ORS 33: Poster 1360.

Bowden, A. E., Y. P. Shkolnikov, D. MacDonald and S. M. Kurtz (2007). Automated microCT-based damage maps of explanted polymeric TDR components. The Spine Journal, Vol. 7(5S) 128S-129S.

Kurtz, S. M., D. MacDonald, A. Von Ooij, J. Isaza, L. Ciccarelli, R. Ross, A. E. Bowden, A. Gl. Patwardhan (2007). Are one-sided wear patterns predictive of greater clinical wear in mobile bearing total disc replacements? The Spine Journal, Vol. 7(5S) 152S.

Bowden, A. E., S. Rundell, J. Auerbach and R. Balderston (2007). Total disc replacement changes facet contact stresses in extension, lateral bending, and axial rotation. Spine Arthroplasty Summit 7, Berlin, Germany, May 1-4.

Bowden, A. E., Y. Shkolnikov, D. MacDonald and S. M. Kurtz (2007). Development and validation of an automated microct-based technique for mapping damage of explanted polymeric components for TDR. Spine Arthroplasty Summit 7, Berlin, Germany, May 1-4.

Coleman, J., A. E. Bowden, S. A. Rundell, R. P. Nockels and K. T. Foley (2007). Effect of a semi-rigid posterior implant on range of motion and load distribution in the lumbar spine: A finite element study. Spine Arthroplasty Summit 7, Berlin, Germany, May 1-4.

Kurtz, S. M., D. MacDonald, L. Ciccarelli, A. van Ooij, J. Isaza, R. Ross, A. E. Bowden and A. Patwardhan (2007). Are one-sided wear patterns predictive of greater clinical wear in mobile bearing TDRs? Spine Arthroplasty Summit 7, Berlin, Germany, May 1-4.

Rundell, S., A. E. Bowden, J. Auerbach and R. Balderston (2007). Effects of Prodisc positioning on lumbar kinematics as determined using a specimen-specific finite element model. Spine Arthroplasty Summit 7, Berlin, Germany, May 1-4.

Bowden, A. E., J. S. Bergström and S. M. Kurtz (2006). Rim fracture risk of highly crosslinked polyethylene total disc replacements. Spine Arthroplasty Summit 6, Montreal, Quebec, Canada, May 10-13.

Bowden, A. E. and M. L. Villarraga (2006). In situ biomechanical investigation of a total facet replacement using finite element analysis. Spine Arthroplasty Summit 6, Montreal, Quebec, Canada, May 10-13.

Bowden, A. E. and M. L. Villarraga (2006). "In situ biomechanics of total facet replacement using finite element analysis." Proc 21st Ann Mtg of NASS SIPP #4: 140.

Rundell, S., A. E. Bowden, M. L. Villarraga, Q. Zhu and P. Cripton (2006). Validation of experimental implant-bone interface load measurement for a facet replacement device using finite element analysis. Spine Arthroplasty Summit 6, Montreal, Quebec, Canada, May 10-13.

Bowden, A. E., S. M. Kurtz and A. A. Edidin (2005). Biomechanical analysis of polyethylene stresses in the Charit„ total disc replacement. Spine Arthroplasty Summit 5, New York City, NY, May 4-7.

Bowden, A. E., S. M. Kurtz, D. MacDonald and A. A. Edidin (2005). "Long-term 3D wear patterns in retrieved acetabular liners." Trans ORS 31: Poster 0668.