Patient selection and surgical technique among ways to avoid TDA revisions

Revisions of primary total disc arthroplasty procedures, which may be required for a number of reasons, can be associated with complications and, according to several surgeons who spoke with Spine Surgery Today about this topic, the approach for a revision can directly affect the outcome of the surgery.

The long-term data for lumbar and cervical total disc arthroplasty (TDA) are very positive, Scott L. Blumenthal, MD, of the Texas Back Institute, in Plano, Texas, said. He said research has shown that patients who undergo primary TDA will need additional surgeries one-third less often than patients who undergo a fusion initially.

 

However, like any procedure, there are certain reasons why a revision may need to take place. Lumbar and cervical TDA revisions are vastly different and should be considered separately, Blumenthal said.

Lumbar revisions more common

Cervical TDA revisions are done less often than lumbar TDA revisions, in my experience, Blumenthal said.

“I have done three revisions in the cervical spine and all were revised to another disc replacement. Technically this is not difficult. This is not the case with lumbar revisions,” he told Spine Surgery Today.

Jeffrey A. Goldstein, MD, a Spine Surgery Today Editorial Board member, said revision rates for lumbar and cervical TDA procedures are low, and the implants are usually very stable if correctly positioned within a patient.

“It is important to place the implant so as to recreate the center of rotation of the disc space. Typically this means getting the implant posteriorly within the disc space. Oversizing the implant can affect the facet joints. Excessive stretch on the facet capsule can be a source of pain. Certainly risks can include expulsion, dislocation or migration. The most common need for revision surgery includes persistent pain or adjacent segment degeneration (ASD),” Goldstein told Spine Surgery Today.

Approach patient considerations

Using an anterior lumbar approach to place an artificial disc prosthesis is relatively straightforward for the surgeon, but can lead to exceedingly difficult revisions because there are many large arteries and veins in front of the lumbar spine that, if damaged, can cause significant bleeding and blood loss, Blumenthal said.

Artificial disc revisions of any kind can be needed due to poor patient selection, surgical technique or because a patient did not follow the postoperative rehabilitation protocol, so the surgeon needs to focus on these areas, he said.

According to Blumenthal, the gold standard for revision of lumbar TDA is likely to convert it to fusion.

“I have done some exchanges with components, but it is exceedingly rare. For obvious reasons, fusion is the salvage procedure. If you can perform the procedure through a posterior approach it is much safer for the patient,” he said.

Patient selection is key

According to Neil M. Badlani, MD, of Houston, patient selection is the number one reason for revision of TDA and is also the best way to avoid a revision in the future.

He discussed the importance of making sure patients are aware of what an artificial disc can do for them, which can go a long way to tempering expectations, as well.

“The most important step is patient selection and managing the expectations of a patient. A patient who does have primarily back pain and is treated with a disc replacement sometimes has to understand it may not eliminate all of their back pain, but it should help them. During their procedure, you need to preserve the bony endplate to minimize fracture and implant subsidence. You have to be careful to place the implant symmetrically in the center of the disc space. You need to take more time in the operating room getting X-rays, making sure the positioning is appropriate. Then you have to be careful when placing the polyethylene to get the right size to allow for motion of the implant,” Badlani said.

Rare reasons for revision

Even with the necessary precautions and proper patient selection, the failure of an artificial disc related to its mechanics is also a possibility, albeit a rare one, according to Badlani.

“The third category is device-related adverse effects: loosening of the implants or wear of the polyethylene or extrusion of the polyethylene. Frankly, those are rare, but that is another category we have to think about. As we get a longer follow-up on these implants, we might see more of that,” he said.

Domagoj Coric, MD, of Carolina Neurosurgery & Spine Associates, in Charlotte, N.C., said displacement or subsidence of an artificial disc are two potential complications that may lead to TDA revision, and these complications occur in less than 1% to 2% of cases.

Bone quality matters

To avoid subsidence or displacement, surgeons should initially determine if a patient is osteoporotic.

“The way to avoid subsidence or displacement is to make sure you have adequate bone quality. If there is any question about a female over 40 [years] or male over 50 [years] with risk factors for osteoporosis, you get a DEXA scan. Typically speaking, you would not want to place a TDA device in someone with less than a -1.0 to -1.5 DEXA score,” he said.

Another potential complication following TDA is heterotopic ossification (HO), where bone surrounding the implant begins to grow up and around the disc. To avoid problems with HO, Coric said the surgeon needs to get the best fit of the primary implant and maximize the footprint of the device within the disc space.

“When I do my arthroplasties, I do not even use my drill at all. I tell them not even to open the drill. I want to keep the bony endplates intact as much as possible. By doing that you decrease subsidence and displacement and you decrease the risk of HO. To avoid bone growth around the device, we avoid drilling, minimize violation of the bony endplates and maximize the footprint for the device to fill up as much of the vertebral endplate as possible. You want to get as good a fit as possible. Afterwards, we routinely use 2 weeks of NSAIDs. Intraoperatively, you want to irrigate very copiously, making sure there are no bone chips or bone debris and place bone wax on any exposed cancellous bone,” Coric said.

Fusion after arthroplasty

If the TDA fails completely, a revision to remove the disc is always a possibility and a fusion can then take place, said Badlani, who discussed some optimal revision strategies.

“If it is a disc replacement, one option for revision is a repeat anterior approach, removal of the implant and fusion. The revision anterior approach can be challenging because of scar tissue and the vascular anatomy. If there are arthritic changes of the disc space or resection of too much bone or malalignment, revision to another arthroplasty may not be possible. In any of those situations, it is safe to revise to a fusion through a standard anterior approach,” he said.

Badlani said, “If you are worried about scar tissue from a revision approach, particularly in the lumbar spine, there are reports of doing a lateral or transpsoas approach to try to retrieve the implant and then place a lateral interbody cage. That is a more unique and creative approach to revise this type of implant in certain situations.”

Disc-for-disc possible

Although fusion for a failed primary TDA is certainly a useful approach, Blumenthal said it is also possible to do a disc-for-disc transplant in some patients.

“When failures occurred and revisions were needed, thinking about our cervical education, we said, typically you take the disc out and replace it with a fusion. However, 7 years or 8 years ago, I had a patient who had a disc replacement and the prosthesis wore out. She asked why she could not have another disc replacement,” Blumenthal said, noting that he explained to the patient they had never considered that option before.

He told Spine Surgery Today that, as result, “I have done now three disc-to-disc revisions. It is much more reasonable than a cervical fusion for a number of reasons. The exposure is better and this is a real option in terms of revision,” Blumenthal said.

Revision due to pain

Pain, rather than implant modification, is one of the most common reasons for TDA revisions, according to Goldstein.

“Typically the need for revision is related to pain. There may be pain generators for which the disc replacement is not anticipated to provide relief. Take note of the facet joints preoperatively. If the facet joint is later found to be a pain generator, then conversion to a fusion with posterior instrumentation may be a consideration,” he said.

After a decision is made to revise or remove an artificial disc implant following primary TDA, access surgeon Salvador A. Brau, MD, FACS, told Spine Surgery Today the approach for a revision is important to a patient’s well-being and outcome.

If the artificial disc is not displaced, Brau will typically suggest leaving the disc in place and proceed with fusion through posterior instrumentation. The remaining device acts as a spacer, he said, and in the majority of patients this will work.

“The other situation would be the disc is displaced, it has left the disc space and it may pose a danger to the vessels in the front, if it has been displaced anteriorly, or it may be of danger to the spinal cord if it has been displaced posteriorly. Laterally, there are not too many entities that can be damaged except for the ureter, so a left ureteral catheter is placed just prior to the procedure,” Brau said.

When the decision is made to remove the disc device, Brau said the approach used is typically determined by the disc level since each level requires a different approach for the best possible surgical outcome.

In addition, prosthesis removal is facilitated in patients who previously had an anti-adhesion barrier deployed at the time of the arthroplasty.

Brau discussed what is required to remove a TDA prosthesis at L5-S1.

“Usually the initial disc is placed through the left retroperitoneal approach, so I would do a right retroperitoneal approach to get to that space. If they did a right retroperitoneal approach, I will do a left retroperitoneal approach for the revision. That usually works well for removing a device at L5-S1. If I have a barrier at L5-S1, it is not a difficult operation. If I do not have a barrier, it becomes more challenging,” he said.

A difficult level

By far the most difficult revision level is L4-5, as 92% of all vascular injuries will occur there. For revisions needed at that level, it is best to go either a little above or a little below where the original tissues were displaced to try and reach the psoas muscle, since this muscle can serve as a landmark that surgeons can follow down or up to the disc, Brau said.

If an anti-adhesion barrier was used, the surgeon can more readily expose the disc space to remove the disc implant.

“It is a lot more difficult if there is no barrier, because the vessels are almost impossible to mobilize. I try to find the edge of the vessels, which is not easy to do, and try to mobilize them. You usually find they cannot be mobilized, so then I go as far anterior as I can without injuring them, and start to go laterally and peel the psoas muscle off the disc space, and then through that window we are able to access the disc space and take out the disc,” Brau said. “It is very challenging, but it can be done, and in my hands and the spine surgeons I work with, we are at about 90% success with removing them without injury.”

Polyethylene inserts

When it comes to removing the artificial disc, it is important to first evaluate a patient’s MRI to see where the vessels are, if any component of the prosthesis has dislocated or if there are visible blood clots. Some TDA prostheses have polyethylene inserts that need to be removed before the endplates of the prosthesis can be removed, Brau said.

He said many surgeons think the artificial discs with a keel are more difficult to remove because of the keel, but once the polyethylene insert is removed, the keel can be taken off both above and below, which provides plenty of space to explant the endplates and remove the disc laterally. However, the procedure is challenging, and patients should be educated on the potentially dangerous complications they may face due to revision surgery, Brau said.

If a procedure is not going as planned or not going well, it can be aborted to keep a patient safe, he said.

Adjacent level revisions

Following TDA, adjacent levels may also require revision or added treatments.

“The longer-term studies have shown the need for surgery at the next level is significantly less in arthroplasty when compared with fusion. Fusion transmits the forces to the next level, and clinically, we see the need for more surgery,” he said.

If adjacent-level surgery is needed, Goldstein said fusion in combination with TDA, which is a hybrid procedure considered off-label by the FDA, can be effective.

“The procedure can be effective. Depending on the implant already in place, the surgeon may need to consider a zero profile device at the adjacent level so the instrumentation can be seated,” he said.

Options for adjacent levels

Adjacent-level treatments following TDA leave the surgeon with several options, according to Coric, which is in contrast to fusion, which basically just leads to more fusion.

“If you are not getting adjacent stresses, you can do a foraminotomy at the adjacent level. If someone comes in with unilateral radiculopathy, not a lot of neck pain or degenerative change, I am going to go posteriorly, do a minimally invasive surgical foraminotomy, which is also a motion-preserving operation. You are not going to get any fusion or instrumentation. I think you have a little bit more leeway with what to do with adjacent levels, when with fusion you are typically looking at more fusion. As you get more fusion you lose more motion, and as you lose more motion, that gets redistributed at adjacent levels and can have a cascading effect,” Coric said.

Badlani said he would treat the adjacent level like any other level if additional treatment were indicated.

“If there is moderate disc degeneration and motion in the facet joint, and you think that level is symptomatic, I would consider an adjacent-level disc replacement. If there are degenerative changes, then disc replacement might not be the answer. I would treat it similar to any other level,” Badlani said.

Because of a lesser need for TDA revision and reduced chances of ASD, Blumenthal is a proponent of TDA over fusion in patients who are eligible for either treatment.

“When you are talking about revisions, the long-term data show disc replacements need less surgery down the road. If someone is a candidate for either one, disc replacement is a better option,” Blumenthal said. – by Robert Linnehan