• Steven A Rundell, Judd S Day, Jorge Isaza, Steven Guillory, and Steven M Kurtz.
• Armstrong Forensic Engineers, Milford, MI 48381, USA. steve.rundell@gmail.com
• Spine. 2012 May 1;37(10):E590-8.

Study DesignA 3-dimensional finite element model of 2 lumbar motion segments (L4-L5 and L5-S1) was used to evaluate the sensitivity of lumbar total disc replacement (TDR) impingement to disc height distraction, spinal sagittal orientation, implant position, and implant lordosis. The models were implanted with a mobile-bearing TDR and exposed to simulated sagittally balanced erect posture.ObjectiveThe objective of this study was to determine the sensitivity of TDR impingement to disc height distraction, implant lordotic angle, implant anterior-posterior position, and spinal orientation relative to the horizon.Summary Of Background DataTDR has the potential to replace fusion as the "gold standard" for treatment of painful degenerative disc disease. However, complications after TDR have been associated with device impingement and accelerated polyethylene wear.MethodsA previously developed finite element model of the lumbar spine was altered to include implantation of a mobile-bearing TDR. A series of sensitivity analyses was performed to determine impingement risk. Specifically, spinal orientation, disc height distraction, footplate lordotic angle, and anterior-posterior position were evaluated.ResultsGenerally, TDR tended to result in an increase in extension rotation and facet contact force during simulated erect posture when compared with the intact models. Impingement risk was sensitive to all of the tested parameters.ConclusionThe data from this study indicate that lumbar mobile-bearing TDR impingement is sensitive to disc height distraction, anterior-posterior position, implant lordosis, and spinal sagittal orientation. TDR impingement risk can be minimized by choosing an implant with an appropriate amount of lordosis, not overdistracting the disc space, and taking care not to place the implant too far anterior or posterior.

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