Lumbar total disc arthroplasty still relevant in select patients

When it was introduced in 1984, lumbar total disc arthroplasty came with promises of pain reduction and preserved or increased mobility, which fusion could not provide. Nearly 30 years later, data show the procedure has not yet demonstrated its superiority to fusion, but surgeons in Europe continue to endorse its use in a select patient population.

“I still am a believer that disc replacement helps a certain group of patients better compared with fusion,” said Luiz Pimenta, MD, PhD, of the Instituto de Patologia da Coluna, in São Paulo, Brazil, who is president of the International Society for the Advancement of Spine Surgery (ISASS). “The concept in the beginning and still the concept now is that, especially for younger patients, the option to preserve motion is better than a fusion. Basically, fusion just postpones problems. We fuse one level and after some years, the patient comes back with another level with degenerative disease,” he told Orthopaedics Today Europe.

Freeman and Davenport found in their systematic literature review on the subject in the European Spine Journal in 2006 that no study at the time had shown clinical outcomes of lumbar total disc replacement were superior to fusion. In a meta-analysis published in 2010, Yajun and colleagues noted lumbar total disc arthroplasty (TDA) did not show significant superiority over fusion for degenerative disc disease and its benefits of motion preservation were not conclusive. In a systematic review of the literature published this year, Jacobs and colleagues concluded the differences in clinical improvement with lumbar TDA compared with fusion and conservative treatment were clinically irrelevant, and they warned against widespread adoption of the technique.

But European orthopaedic surgeons remain proponents of lumbar TDA for different reasons.

“Originally, it was said that it is highly important that you maintain motion for the patient,” Max Aebi, MD, DHC, FRCSC, professor and co-chair emeritus at the MEM Research Center of Orthopaedic Surgery at the University of Bern, Switzerland, said. “But the patient goes to the doctor because of pain — not because of motion. With time, I think most of the surgeons understood that the major issue of the patients is not so much to maintain a few degrees of motion, but maybe to protect the segment above or below to decelerate disc degeneration,” said Aebi, who is an Orthopaedics Today Europe Editorial Board member.

Rudolf Bertagnoli, MD, professor of orthopaedics at First European Center for Spine Arthroplasty and Associated Nonfusion Technologies, in Bogen, Germany, agreed that reduced disc degeneration at other levels is a benefit of lumbar TDA.

“We now have up to 15 years of follow-up in some cases that shows we have a much significantly lower rate of adjacent-level degeneration,” he said. “This is one of the major problems of fusion procedures: The uninstrumented segment adjacent to the fusion procedure will have to work much more, which means we see a relatively higher rate of degeneration at the adjacent levels after fusion procedures.”

Relevant patient population

After years of TDA experience, surgeons implemented more select criteria for determining which patients are candidates for lumbar TDA. The procedure is now reserved for young patients, aged 50 years or younger, with isolated disc degeneration, typically Modic 1 changes on MRI, and with nonarthritic facets and posterior muscles that are strong, according to Jean Charles Le Huec, MD, PhD, professor of orthopaedic surgery, chairman of the ortho-spine department and director of the Surgical Research Lab at Bordeaux University Hospital, in Bordeaux, France.

“Lumbar total disc arthroplasty is not indicated for patients with osteopenia or osteoporosis because the risk for subsidence would lead to failure of the implant bone interface,” said Bertagnoli, an Orthopaedics Today Europe Editorial Board member. “We also do not recommend this in the elderly population because the majority has low bone density and osteopenia.”

Pimenta, who began doing TDA surgery in 2000, learned that disc replacement performed for the wrong indications can lead to more surgery and revisions.

“The segment of motion is not the disc itself — it also has two other joints in the back, including the facet,” he said. “To preserve the motion, we have to preserve the facet. If the facets are in bad condition when we do a disc replacement, it will in the long run cause more problems, recurrent pain and the need for revision.”

In the 1990s, Enric Càceres Palou, MD, PhD, FRC, head of orthopaedics at Valle Hebron Hospital and chair of Autonomous University in Barcelona, was the first surgeon in Spain to implant lumbar TDA prostheses. He suggested lumbar TDA not be performed in patients older than age 55 years.

According to Càceres, who is second vice president of the European Federation of National Associations of Orthopaedics and Traumatology, lumbar TDA should only be considered for patients with low back pain who do not improve after at least 6 months of conservative and other nonoperative treatment, including medication and activity modification.

“Low back pain from degenerative changes of the lumbar spine is mostly related to disc degeneration,” he said. “The surgeon, using the appropriate diagnostic tools, including X-ray, MRI and semi-invasive tests, faces the challenge of identifying patients in whom the disc is the predominant source of back pain.”

Càceres said ideal candidates for TDA should have not undergone previous abdominal surgery because scarring can complicate the anterior approach and they need a normal vascular anatomy.

“Patients should be neither extremely thin nor obese; either body type can complicate the anterior approach,” he said.

Lordosis, endplates, sagittal balance

To identify the ideal candidate for TDA, surgeons should assess the spinal lordosis particularly at L5/S1, Càceres said.

“A less lordotic disc space eases the seating of the prosthesis intervertebrally. Sufficient mobilization is easier because of less tension on the posterior portion of the disc space,” he said.

He said surgeons should avoid the procedure in anyone with a deeply concave superior endplate or large anterior osteophytes because this can complicate positioning the disc arthroplasty plates. Patients need 5 mm or more of disc space height for adequate distraction and mobilization and preoperatively surgeons should determine the vertebral body depth, according to Càceres.

Le Huec, who is past president of the Spine Society of Europe and ISASS, said sagittal balance is an important indication for determining which patients are candidates for lumbar TDA. When he and his colleagues included all their lumbar TDA cases in a registry, which included full-standing anterior-posterior and lateral radiographs, they found patients with a high incidence angle greater than 60º who underwent TDA had significantly worse outcomes mainly due to facet problems and persisting pain.

“This parameter (>60º sagittal balance) is an exclusion criterion for us,” Le Huec said. “In our experience, 20% to 25% of the patients [at] between 6 months and 2 years have pain, and those suffering from facet pain are always those... with a high incidence angle, which is the parameter for sagittal balance. These patients are not good candidates for disc arthroplasty.”

Training is essential to a successful lumbar TDA. When done properly, the complication rate for total disc replacement is very low, Le Huec said.

“We have never seen an anterior complication that we were not able to repair,” he said.

Various implant designs studied

Since lumbar TDA was introduced several implant designs have been used, which Szpalski and colleagues noted in their 2002 review where they chronicled designs in the literature and patents granted in the field.

About 25 models of lumbar TDA prostheses are used worldwide and three of them seem to stand out from the others, according to Bertagnoli: the Charité implant (various manufacturers), ProDisc L Total Disc Replacement (DePuy Synthes Spine; West Chester, Pa., USA) and Maverick lumbar prosthesis (Medtronic Spinal and Biologics, Memphis, Tenn., USA). The first disc prosthesis, the Charité implant, was introduced in 1984, followed by the ProDisc device in 1990.

“Generally speaking, the results approximately 2 years after surgery were similar to anterior as well as posterior fusion surgery,” Aebi said.

The ProDisc and Maverick devices have the longest follow-up, with successful outcomes in U.S. Food and Drug Administration prospective randomized studies, according to Le Huec. The first 64 patients implanted with the ProDisc demonstrated mechanical stability, pain relief and improved functional status with preserved motion at 7-year to 11-year follow-up, according to data from Marnay published in 2002. The Maverick implant, which was first implanted by Le Huec in 2002, showed improvements that equaled those with anterior fusion cages at 2 years postoperatively in a study Le Huec and colleagues conducted.

“Then many prostheses arrived on the market, but they were all copies of the previous ones that all had the ball-and-socket principle,” Le Huec said, noting the main articulation differences were the Charité TDA device had a free ball and there was a fixed ball in the ProDisc and Maverick designs. In the latter, the center of rotation differed and the couple of friction was either metal-on-metal or metal-on-polyethelene, he said.

But, no one TDA implant appears to perform better than the others, according to Le Huec and Aebi.

“The most frequently used discs like the ProDisc and Charité are successful due to systematic training of the surgeons,” Aebi said. “But not significantly different results can be reached with almost all disc prostheses presently established in the market, including new concepts like monoblock disc replacement with polyurethane devices.”

The Charité had a high complication rate due to surgeon inexperience and bone fixation was problematic in its first generation design because it lacked a hydroxyapatite coating. Furthermore, it was associated with high rates of facet arthrosis at 2 postoperative years, Le Huec said.

Because the Charité prosthesis is unconstrained, Pimenta found his patients often developed instability and then he had to revise them.

The most successful technology is the semiconstrained disc, Bertagnoli said.

“It is forgiving and it takes over the control of the motion segment,” he said. “This is, I think, why this has been the most universally used disc prosthesis.”

Pimenta said it is important that the lumbar anatomy naturally constrains the implant.

“Using a lateral design, we have the ligaments in the front that would restrict excessive motion. We have the facet that also restricts excessive motion, so we don’t have an unconstrained disc and it has a more controlled motion,” he said.

Some TDA devices, such as the ProDisc O Total Disc Replacement (DePuy Synthes Spine; Hagendorf, Switzerland), are intended to be implanted via a lateral approach. Pimenta has performed about 150 lumbar TDA surgeries using that approach and a minimally invasive technique.

To preserve motion, it is critical to not disrupt structures around the spine, Pimenta said.

“When we do a disc replacement, we make sure our surgery is minimally invasive so that we don’t damage muscle, damage ligaments, remove unnecessary bone, etc. This technique has yielded a better success rate,” he said.

Multilevel replacement considerations

Some surgeons believe only one lumbar level should be replaced at a time, however, Càceres contends multilevel TDA can be done in exceptional cases.

“Less than 10% of these procedures are indicated in multiple-level disease,” Càceres told Orthopaedics Today Europe. “The results could be good in cases of good patient selection with two or three degenerative discs without sciatica.”

Bertagnoli is not opposed to multilevel disc arthroplasty but noted that surgeon training needs to be much more extensive than for a single-level replacement. “The critical issue is the right positioning of the implant and the synchronization of each implant to the other implants. We have significantly better results with multilevel motion preservation with total disc replacement than with a multilevel fusion,” he said.

However, studies that compare multilevel TDA to fusion are lacking. Càceres said the few studies that evaluate multilevel procedures showed results were similar to one-level replacement.

Aebi told Orthopaedics Today Europe, “We need prospective, randomized, controlled studies to establish indications for when to perform multilevel replacement, specifically in comparison with fusion surgery in multilevel degenerative lumbar disease.”

“There are few case series that claim satisfying results, but without any control. Therefore, multilevel disc replacement should not be recommended to patients or to the average surgeon,” he said.

Le Huec said, “The very limited series in the literature have never convinced me to do multilevel implantation as the biomechanics of our implants today are very basic.”

He uses a hybrid construct in patients with multilevel degenerative disc disease. For patients with degenerative disc disease on both levels, “We prefer to perform a fusion at level L5/S1 and implant a prosthesis at level L4-5,” he said. “Our experience and the experience of other teams have shown that two levels of disc arthroplasty doesn’t provide as good of an outcome compared with this hybrid construct.”

Implant removal, explantation

Lumbar TDA carries three main potential complications, according to Aebi: (1) complications related to disc space access through the anterior approach because of the major vessels; (2) wrong positioning of the disc device; and (3) later complications where the disc prosthesis degrades or subsides into bone.

“It is important that these disc replacements are really down in the disc space and, with most prostheses, there are special instruments with which you can basically position the prosthesis into the disc space,” he said.

Some surgeons say the indications for implant removal include dislocation or infection.

“The salvage procedure is difficult with a high risk for major complications,” Càceres said.

Pimenta said surgeons must consider a revision strategy during primary lumbar TDA.

During primary implantation, Le Huec and colleagues have used two techniques to facilitate potential revision: inserting the prosthesis with an oblique approach, first possible with the Maverick prosthesis in 2003, and using a special barrier to protect the vessels during primary TDA. Le Huec said the Gore Preclude Vessel Guard polytetrafluoroethylene membrane (W. L. Gore & Associates Inc., Flagstaff, Ariz., USA) makes it easier to dissect the anterior spine during a revision and “facilitates revision because there are no adhesions with the left iliac vein, for instance.”

Occasionally a new disc prosthesis may be placed after an explantation. But an anterior fusion is typically done afterwards, either alone or with a cage, with additional anterior fixation through the cage or with a plate, Aebi said.

“It may be necessary to combine it with a posterior surgery and instrumentation. Sometimes you may want to leave the artificial disc in place and only perform a posterior instrumented surgery and put the anterior column with the remaining disc prosthesis under compression through the posterior tension banding of the instrumentation,” he said.

Future of lumbar TDA

Other techniques have been presented as alternatives to lumbar TDA, including posterior dynamic stabilization, facet replacement, interspinous process devices, anterior interbody fusion, far lateral interbody fusion and transforaminal lumbar interbody fusion with minimally invasive technology. Many of these procedures have been accepted and successful, Pimenta said.

Newer elastomeric disc prostheses have been used in lumbar TDA, but surgeons do not have enough experience with them to determine their advantages over the mechanical-style discs. Pimenta expects disc replacement will eventually better mimic and preserve lumbar spine motion for a longer time.

“We need to prove that the disc replacement lasts for at least 10 [years] to 20 years,” he said. “Having a lateral approach with an elastomeric disc is, in my opinion, the best move for the future.”

“There is a place for lumbar disc arthroplasty with the indications presented, but we still have a lot to do to improve the biomechanics of the implants as today [they are] too basic,” Le Huec said. “Probably the future will show that some drug therapy and less aggressive techniques could have a similar effect to slow down the degenerative process and therefore decrease pain and maintain function.” – by Tina DiMarcantonio

• References:
• Freeman BJ. Eur Spine J. 2006;15(Suppl 3):439-447.
• Jacobs WC. Spine. 2013;38:24-36.
• Le Huec JC. Orthop Clin North Am. 2005;36:315-322.
• Marnay T. Spine J. 2002;2(5):94S.
• Szpalski M. Eur Spine J. 2002;11:S65-S84.
• Yajun W. Eur Spine J. 2010;doi:10.1007/s00586-010-1394-x.

• For more information:
• Max Aebi, MD, DHC, FRCSC, can be reached at Stauffacher Str. 78, CH-3014 Bern, Switzerland; email: max.aebi@memcenter.unibe.ch.
• Rudolf Bertagnoli, MD, can be reached at Mussinanstr. 6, 94327 Bogen, Germany; email: rudolf.bertagnoli@pro-spine.com.
• Enric Càceres Palou, MD, PhD, FRC, can be reached at Passeig Vall d’Hebron, 119-129, 08035 Barcelona, Spain; email: ecaceres@vhebron.net.
• Jean Charles Le Huec, MD, PhD, can be reached at the Ortho-Spine Department, Bordeaux University Hospital France, Rue Jean Burguet, 33000 Bordeaux, France; email: j-c.lehuec@u-bordeaux2.fr.
• Luiz Pimenta, MD, PhD, can be reached at Rua Vergueiro, 1.421 Top Towers Offices, Torre Sul, Sala 305, Paraíso, 04101-000, São Paulo, Brazil; email: luizpimenta@luizpimenta.com.br.

Disclosures: Aebi is a member of the Scientific Board of Ranier Limited, the producer of the Cadisc prosthesis, in Cambridge, UK. Bertagnoli is a consultant for Synthes Spine. Pimenta is a stock owner and consultant for Nuvasive Inc. Càceres Palou and Le Huec have no relevant financial disclosures.

How has lumbar total disc arthroplasty lived up to its original clinical expectations of pain reduction and increased spine mobility?

 

Surgeons are reluctant to perform lumbar disc arthroplasty

Lumbar total disc arthroplasty was expected to replace spinal fusion for the treatment of chronic low back pain in patients with disc degeneration.

The number of fusions performed for low back pain has continued to increase despite trials reporting that the effectiveness of this operation is only comparable with multidisciplinary rehabilitation including cognitive treatment and exercises. The number of disc arthroplasties performed, on the contrary, has been stable and constitutes only a small percentage of those patients operated on for disc degeneration. Trials have not shown that arthroplasty is more effective than fusion in reducing low back pain. One trial found statistically better results compared with multidisciplinary rehabilitation, but the difference was not considered of clinical benefit by an independent systematic review. Adjacent-segment disc degeneration has been regarded as a disadvantage of spinal fusion, but the knowledge of this occurrence is currently sparse and radiological findings are not associated with pain and disability.

Lumbar total disc arthroplasty has been regarded as a dynamic alternative, which means patients will regain normal spinal mobility. Recently published biomechanical studies suggest the prosthesis may behave more like a fusion than a healthy dynamic disc. In the long term, adjacent-segment disc degeneration may also be expected after disc arthroplasty.

At first glance, a dynamic disc prosthesis may appear to be an attractive alternative for the patient, but surgeons are reluctant to implant these devices, partly because of the available clinical results and partly because they do not like to reoperate on these patients.

Jens Ivar Brox, MD, is a consultant and researcher in the orthopaedic department, Oslo University Hospital, Oslo, Norway.
Disclosure: Brox has no relevant financial disclosures.

 

Devices are lacking conceptually

For me, the answer is clear that lumbar total disc arthroplasty (TDA) has not lived up to its clinical expectations. The great hope of its proponents was that it would produce the same changes in the life of patients as those produced by the introduction of hip and knee arthroplasty. But there is a major difference: A hip or knee arthrodesis results in major disability, but that is not the case with most lumbar fusions, which have a limited effect on mobility.

Secondly, the hip joint is a simple ball joint and its movement is simple to reproduce. Total hip replacement replaces about 90% of the function of the hip. The spine is not a single joint like the hip, but a three-joint complex with elaborate mechanical movements and a viscoelastic load-sharing action. Most lumbar TDA devices on the market have forgotten that. We have done metal-metal or metal-plastic couples similar to a hip replacement that we place between two vertebrae. Basically, that reproduces only part of the motion and function without addressing the important disc viscoelasticity and load-sharing properties. So that first problem is a conceptual problem. Some designs tried to resolve the issue. Most did not succeed as the elastic polymers they used failed under repeated loading. Maybe new designs will offer a solution.

TDA was also supposed to solve the problem of adjacent-level disease, which is not a totally proven concept. There is enough good, long-term literature showing adjacent-level disease or degenerative changes at any level next to or even further away from the fusion may just be the consequence of individual characteristics or natural evolution of the disease (Videbaek, Pellise and Penta). A 20-year follow-up study by Wai showed more levels degenerated nonadjacent to a fusion than adjacent to it. Some longer term studies of TDA showed there is a non-negligible amount of disc degeneration adjacent to the prosthesis (Huang, Putzier).

Finally, if disc arthroplasty fails—and failures occur—revision is a complex and sometimes life-threatening surgery.

Projections in 2004 predicted that by 2010 the U.S. spine surgery market would comprise 45% artificial discs, 28% dynamic posterior stabilization and 19% artificial nucleus devices, and that fusion would retain 5% of the market (Viscogliosi). However, artificial disc today is about 3% of the U.S. market and artificial nucleus is virtually nonexistent. It seems the actual concept of TDA did not fulfill surgeon expectations. One day artificial discs may revolutionize the treatment of lumbar degenerative disease, but that does not appear to be the case today.

Marek Szpalski, MD, PhD, is chairman of the department of orthopaedics, Iris South Teaching Hospitals and associate professor of orthopaedics, University of Brussels, in Brussels, and adjunct associate professor, New York University, New York.
Disclosure: Szpalski has no relevant financial disclosures.

• References:
• Huang RC. J Spinal Disord Tech. 2003; 16:435-440.
• Pellisé F. Spine. 2007; 32:574–579.
• Penta M. Spine. 1995; 20:743-747.
• Putzier M. Eur Spine J. 2006; 15:183-195.
• Videbaek TS. Spine. 2010; doi:10.1097/BRS.0b013e3181e57269.
• Viscogliosi AG, Viscogliosi JJ, Viscogliosi MR. Beyond total disc: The future of spine surgery. Viscogliosi Brothers LLC; 2004.
• Wai EK. Spine. 2006; 31:1952-1956.