Effect of Center Keel Design ADRs on Vertebral Structural Integrity

[Researcher]

Yesterday, I was introduced to a spinal surgeon relatively new to our area. He happens to go to church with a co-worker. He moved here from California to be closer to his family. As it turns out, he is very knowledgeable about artificial disc replacement, having implanted them in California and here already as well. I have an open invitation from him for future discussions, and he is helping me by reviewing my MRI and X-Ray images. I am very encouraged that I now have an expert in the field that I can talk to, not as a "surgeon", but as the friend of a friend. I can call him on his cell phone or send him an email any time I like. I will share more about him specifically in the future after I have received his permission.

In the meantime, I want to ask one question based on a statement he made during our discussion yesterday. He cautioned me about selecting ADRs with a large center keel design. Examples of ADR's that have this type of design include the Synthes Spine Prodisc-C and Globus Medical Secure-C.

Prodisc-C



Secure-C


He indicated that some patients using this type of ADR have experienced the formation of cracks in the vertebral body and that the large channel required by these designs may be related to this complication. Of course, these cracks could be the result of other variables unique to the individual patients and the implant process. I was wondering if anyone has heard of this issue before. I am not making the statement that the two products shown above have known problems. I merely chose them as visual examples of a large center keel design.

Thanks,

Phil

p.s. - He had some not so encouraging news regarding insurance coverage for ADR. He said that every appeal that he has made to BCBS of Alabama has been denied. However, he did indicate that there has been some success in getting reimbursed for the portion of the ADR procedure that is identical to ACDF, which should be a significant percentage. i will provide more details on this as I continue my discussions with him.

Disclaimer: None of the information in this post should be considered medical advise. I am not a medical professional and any information presented, even though it may have originated from a medical professional is purely for the purpose of patient education and discussion.

[KBear]

Phil, I have heard of these problems. I think that is why we are seeing the new discs coming out doing away with the center keels (this is pure speculation on my part).

[trkdoc714]

From my understanding, once the bone growth begins, it grows around and through the device.

During the follow up visits with the local surgeon I asked that exact question. His PA said once the bone growth was complete there was little chance of a fracture related to the implant procedure.

I hope he's right. That was the same answer I got from Dr. Ritter-Lang prior to surgery.

[Justin]

Hi Phil,

Thanks for sharing the information above.

He indicated that some patients using this type of ADR have experienced the formation of cracks in the vertebral body and that the large channel required by these designs may be related to this complication. Of course, these cracks could be the result of other variables unique to the individual patients and the implant process. I was wondering if anyone has heard of this issue before. I am not making the statement that the two products shown above have known problems. I merely chose them as visual examples of a large center keel design.

Thanks,

Phil

With keeled devices, great attention must be paid to the size (height) of the patient's vertebral bodies. One concern with keeled devices at multiple adjacent levels is creating a fracture of the vertebral body, as you mentioned in your post. I have seen literature mentioning this complication in the past.

[MDE]

As Justin mentioned, literature has stated this issue, but almost exclusively with multi-level ADR surgeries with devices that have midline keels both on the superior and inferior endplates. Some devices only have a keel on the superior endplate, and others offer "options" so that in multi-level cases, a non keeled version can be used. This is also very directly related to technique in preparation of the endplate and the slot for the keel (how it was milled or drilled and how much bone was removed prior to trying to press fit the keel into place)

[tyler]

I want to ask one question based on a statement he made during our discussion yesterday. He cautioned me about selecting ADRs with a large center keel design. Examples of ADR's that have this type of design include the Synthes Spine Prodisc-C and Globus Medical Secure-C.

Prodisc-C



Secure-C


He indicated that some patients using this type of ADR have experienced the formation of cracks in the vertebral body and that the large channel required by these designs may be related to this complication. Of course, these cracks could be the result of other variables unique to the individual patients and the implant process. I was wondering if anyone has heard of this issue before. I am not making the statement that the two products shown above have known problems. I merely chose them as visual examples of a large center keel design.
.

Hi Phil -

This same issue was brought up by several of the surgeons I consulted with and apparently it can be a significant concern as noted.

As an initial matter, the larger and thicker the keel placement, the more the adjacent vertebrae must be carved out to accommodate implantation. However, it's not just an implantation issue because a disc will continue to transmit stress loads to the adjoining vertebrae even after it's settled in. To the extent those vertebrae are either weak already (generally a contraindication to ADR in the first place) or become so (it happens to the best of us), the issue can be an important one.

While there are different heights to the core of many discs, my understanding about Prodisc from their product brochure is that the basic keel was 3.5mm high. Since cervical vertebrae can be as thin as 10mm, this can represent a substantial cut-away.

My surgeon and others considered this a significant issue and one of the reasons they favored M6 - which instead has smaller, shorter and thinner 'fins.' I've heard that the Prodisc manufacturer has apparently recognized this potential issue and introduced smaller keels in newer designs, but I don't believe these are yet being used in the U.S.

Good luck in the research - and keep us posted on what you find!

Best,
Tyler

[Carson]

As mentioned I would think the instances of fracture are extremely rare. Here are two images of vertebral split fractures from a radiology website to demonstrate for radiologists abnormal imaging findings in lumbar.

[Carson]

Source Link: Normal and Abnormal Imaging Findings in Lumbar Total Disk Replacement: Devices and Complications

[Justin]

BTW the publications I read concerning vertebral fracture were about the Maverick device. The keels on the Maverick are huge.

[runagain]

Hey, good info. Thanks guys.
Like one of the posters above, i have to wonder if the implantation was done on bone that was not strong enough.
I am going good with no fractures but my bone is very strong.
Researcher, i think I know who your friend is. If he came from San Diego, CA. I have a friend who said he was a very good surgeon and she was really disappointed when he moved.
May be another guy, though.
I think it is good to bounce ideas off people, especially from someone who has a similar experience or from a surgeon friend.

R