Lumbar total disc replacement impingement sensitivity to disc height distraction, spinal sagittal orientation, implant position, and implant lordosis (spine 37;10, E590-598)

Spine 2012 May 1;37(10):E590-8

Title:

Lumbar total disc replacement impingement sensitivity to disc height distraction, spinal sagittal orientation, implant position, and implant lordosis

Authors

Rundell SA

Day JS

Isaza J

Guillory S

Kurtz SM

Study Design

3D finite element model (FEM) of 2 lumbar motion segments (L4-L5/L5-S1) implanted with a mobile-bearing TDR and exposed to simulated sagittally balanced erect posture

Objective

To determine the sensitivity of TDR impingement to 

1) Disc height distraction

2) Implant lordotic angle

3) Implant anterior-posterior position

4) Spinal orientation relative to the horizon

Summary of Background Data

1. TDR has the potential to replace fusion as the "gold standard" for treatment of painful degenerative disc disease.

2. However, complications after TDR have been associated with device impingement and accelerated polyethylene wear.

Methods

1. Previously developed FEM was altered to include implantation of a mobile-bearing TDR.

2. Series of sensitivity analyses was performed to determine impingement risk.

3. Evaluations

   

1) Spinal orientation

    2) Disc height distraction

    3) Footplate lordosis angle

    4) Anterior-posterior position

Results

1. TDR tended to result in an increase in extension rotation and facet contact force during simulated erect posture when compared with the intact models.

2. Impingement risk was sensitive to all of the tested parameters.

Conclusion

1. Indicated that lumbar mobile-bearing TDR impingement is sensitive to disc height distraction, anterior-posterior position, implant lordosis, and spinal sagittal orientation.

2. 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.

Key points

1. TDR implantation during simulated erect posture

>>> increased facet contact force

>>>extension rotation

2. Disc height distraction >>> increasing impingement risk

3. Underestimation of the implant’s lordotic angle >>> greatest impingement risk

4. Placement of the TDR too far anterior or posterior >>> increased impingement risk

5. Patients with an increased sacral slope >>> greater risk of device impingement

"This comes from Spine (c) 2012 Lippincott Williams & Wilkins, Inc."