Biomechanical Effect of Constraint in Lumbar Total Disc Replacement

[Justin]

Spine. 34(12):1281-1286, May 20, 2009.

Biomechanical Effect of Constraint in Lumbar Total Disc Replacement: A Study With Finite Element Analysis.

Chung, Sang Ki MD, PhD *; Kim, Young Eun PhD +; Wang, Kyu-Chang MD, PhD *
Institution From the *Department of Neurosurgery, College of Medicine, Seoul National University, Seoul, Korea; and +Department of Mechanical Engineering, Dankook University, Yongin, Korea.

Study Design. Biomechanical effect of implantation of an artificial disc (AD) was investigated using the nonlinear three-dimensional finite element model of L4-L5. The SB CHARITE and the Prodisc were chosen as the representative prosthesis of unconstrained and constrained ADs (UADs and CADs) and compared with the intact human intervertebral disc.

Objective. To investigate the effect of implantation of an AD to spinal functional unit and to evaluate the difference between the unconstrained and constrained models.

Methods. Intact osteoligamentous L4-L5 finite element model was created with 1-mm computed tomography scan of a cadaveric spine and known material property of each element. Two models implanted with ADs, unconstrained or constrained model, were also developed. The implanted model predictions were compared with that of the intact. Range of motion, force on the spinal ligaments, force on the facet joint, stress on the vertebral body and vertebral endplate with flexion/extension, lateral bending, and axial rotation under 400 N compressive preload were compared among the models.

Results. The implanted models showed increased range of motion in flexion/extension, lateral bending, and axial rotation compared with that of the intact. Under 6-Nm moment, the range of motion were 140%, 170%, and 200% of intact in the UAD model and 133%, 137%, and 138% in the CAD model to each direction of loading. The forces on each ligament were different among the models with various loading conditions. Force on the facet, stress on the vertebral body and vertebral endplate were much larger in implanted model, especially in the CAD model.

Conclusion. By the result of this study it is obvious that implanted segment with AD has large range of motion and suffers from increased loading to surrounding bone and ligaments. The UAD has larger range of motion but exert less loading to the implanted segment than the CAD. It seems that the mobile center of rotation of the UAD has the ability to lessen the facet contact force and stress on the vertebral body.

(C) 2009 Lippincott Williams & Wilkins, Inc.

[Gilbert P]

Hello Doc

I think this means ADR increasea range of motion and further deterates the joints.

Is that correct Could put in layman terms?

Thanks for all the info

ATB Gilbert P

[Justin]

Hello Doc

I think this means ADR increasea range of motion and further deterates the joints.

Is that correct Could put in layman terms?

Thanks for all the info

ATB Gilbert P

Yes, Gil you are right. They looked at both unconstrained and constrained (UADs and CADs) artificial discs (ADs) compared with the intact human intervertebral disc.

An unconstrained device (UAD) is the Charite in this case and the constrained device (CAD) is the ProDisc. Both devices had increased range of motion in flexion/extension, lateral bending, and axial rotation compared with that of the intact human intervertebral disc.

• The UAD, Charite, displayed the greatest increase in range of motion.

• The CAD, ProDisc, displayed the greatest increased force on the facet, stress on the vertebral body and vertebral endplate.

• The forces on each ligament were different among the models with various loading conditions.

The publication's conclusion is great and I hope it makes more sense now:

By the result of this study it is obvious that implanted segment with AD (artificial disc) has large range of motion and suffers from increased loading to surrounding bone and ligaments. The UAD, Charite, has larger range of motion but exert less loading to the implanted segment than the CAD, ProDisc. It seems that the mobile center of rotation of the UAD, Charite, has the ability to lessen the facet contact force and stress on the vertebral body.

[Gilbert P]

Hi All

I stumbled on this from other site and wanted to share this information.

pubmed 19455003

Spine: 20 May 2009 - Volume 34 - Issue 12 - pp 1281-1286

Biomechanical Effect of Constraint in Lumbar Total Disc Replacement: A Study With Finite Element Analysis

Chung, Sang Ki MD, PhD; Kim, Young Eun PhD; Wang, Kyu-Chang MD, PhD
Department of Neurosurgery, College of Medicine, Seoul National University, Seoul, Korea.

Study Design
Biomechanical effect of implantation of an artificial disc (AD) was investigated using the nonlinear three-dimensional finite element model of L4-L5. The SB CHARITÉ and the Prodisc were chosen as the representative prosthesis of unconstrained and constrained ADs (UADs and CADs) and compared with the intact human intervertebral disc.

Objective
To investigate the effect of implantation of an AD to spinal functional unit and to evaluate the difference between the unconstrained and constrained models.

Methods
Intact osteoligamentous L4-L5 finite element model was created with 1-mm computed tomography scan of a cadaveric spine and known material property of each element. Two models implanted with ADs, unconstrained or constrained model, were also developed. The implanted model predictions were compared with that of the intact. Range of motion, force on the spinal ligaments, force on the facet joint, stress on the vertebral body and vertebral endplate with flexion/extension, lateral bending, and axial rotation under 400 N compressive preload were compared among the models.

Results
The implanted models showed increased range of motion in flexion/extension, lateral bending, and axial rotation compared with that of the intact. Under 6-Nm moment, the range of motion were 140%, 170%, and 200% of intact in the UAD model and 133%, 137%, and 138% in the CAD model to each direction of loading. The forces on each ligament were different among the models with various loading conditions. Force on the facet, stress on the vertebral body and vertebral endplate were much larger in implanted model, especially in the CAD model.

Conclusion
By the result of this study it is obvious that implanted segment with AD has large range of motion and suffers from increased loading to surrounding bone and ligaments. The UAD has larger range of motion but exert less loading to the implanted segment than the CAD. It seems that the mobile center of rotation of the UAD has the ability to lessen the facet contact force and stress on the vertebral body.

Something to think about

Gilbert P

[Justin]

Hey Gil, thanks! The publication above has already been posted in the Spine Education Forums. See this thread that already has a discussion going --> click here.

[Gilbert P]

Hi Justin

Sorry I am not paying attention Dealing with pain, building a house for a client, mowing the lawn, trying to ride my bike,Etc...

Thanks again

This disturbed me to find this, does this mean we are doomed?

Sometimes I am not the sharpest tool in the shed and I wonder if their are any tools in the shed

Gilbert P

[KBear]

Sometimes I am not the sharpest tool in the shed and I wonder if their are any tools in the shed

Me either! That's one of my favorite sayings, along with, "not the brightest crayola in the box"

[trkdoc714]

Gil,

We're not doomed by any stretch of the imagination. Abstracts should be read with a grain os salt (or Mr. Dash for the HBP patients).

As I learned, no one's spine is the same. There is no "one size fits all" product or procedure. We have to be researchers and ask a lot of questions. That's why this unbiased site is so important. There aren't any manufacturers, surgeons or spine brokers (medical tour guides) trying to fit anyone into their products.

I truly think one day hybrid operations will consist of different brand artificial discs (or the technology to regenerate them) as they all have different properties and address various other individual issues we might have.

Like you've said many times......Keep learning!

Bob

[Justin]

Hey Gil,

No worries my friend. You've got a lot on your mind -- it doesn't reflect negatively on you in any way. It shows that you are a Spine Patient in pain that has "life" going on around him.

Thank you for bringing this important study up and I merged the threads so that we can have a discussion about it.

Gil, you've actually hit on something vitally important to Spine Patients -- We, as Spine Patients, should read every abstract--no what matter what Journal publishes it--with a "scrutinizing eye," as Bob eloquently stated that all abstracts should be read with a grain of salt (or Mrs. Dash for patients with HTN ). The abstracts in the Spine Patient Education Forums are not "cherry picked" abstracts to help achieve an underlying agenda. Rather, I merely post as many abstracts as I can find that relate to all Spine Patients and I encourage comments and discussion. The abstracts posted within that forum are not locked and anyone is free to post in the Education forum. Like anything in life, some of these abstracts are good, bad and anywhere in between. Just because someone publishes something in a Journal, it doesn't mean it's "off limits" to be questioned. Actually, the exact opposite should happen: it should be scrutinized, as it was "worthy" of publication by an editorial board.

Thank you for your help Gil!