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6 Lumbar Artificial Discs, Their Features, and Clinical Proof Points

Published January 31, 2019

If your back is unresponsive to nonsurgical management, your doctor could recommend total disc replacement (TDR) surgery. When you undergo total disc replacement, the damaged disc in your back is replaced by an artificial disc that affords your spine the near same functionality and flexibility it once enjoyed before injury.

As a chronic back pain patient, it’s important to know and understand what your lumbar implant options are and where you can access them. Choosing the right artificial disc implant for your condition can help regain your quality of life more quickly—whether that’s getting back to work, resuming activities, or doing basic day-to-day chores.

Only two lumbar disc replacement systems have met the rigors of the U.S. Food and Drug Administration Class III Medical Device Approval Process and are currently marketed in the U.S.: the ProDisc-L and the activL Artificial Disc. Several other lumbar disc replacement systems have gone into clinical trial to seek FDA approval but have fallen short for company financial or performance related issues.

 

Methodology

What do we mean by FDA Class III Product?

Medical devices are regulated by the U.S. Food and Drug Administration because let’s face it, no one wants to unknowingly be treated with Snake Oil. Yet the FDA does not treat all types of medical devices equal. For instance, it sees a pair of surgical scissors as just that, scissors, and does not put them through a rigorous clearance/approval process. Even most implants used for spinal fusion just require biomechanical testing and follow what is known as the FDA Class II Process for product clearance. However, the FDA sees artificial disc replacements, whether cervical or lumbar, differently. It believes that the slightest nuance in design characteristics can greatly impact long-term patient outcomes. Therefore, they require that rigorous, long-term clinical data is gathered on such Class III devices. The FDA Class III Approval process is like no other country’s. The perks: at the end we know how the discs will perform over time. 

What do we mean by mean wear rate?
When disc replacements first entered the stage, there was significant concern about the long-term wear rates of the discs. Without long-term evidence available, it was common for surgeons and patients alike to question how long they could expect the replacement to last. 

A test was developed and validated to measure how many years of relative wear a disc could take. It is an extremely time consuming and costly test to run and thus why only the most established companies have done the long-term testing. 

The test measures how many million cycles of continuous use the discs can take. Each ten million cycles represents a year and the test is validated out to 80 years. Orthopaedic surgeons understand the long-term wear rates of knees and hips so those implants are commonly used to compare the wear of disc replacements. 


The Lumbar Artificial Discs

We've put together a list of six lumbar artificial disc implant technologies available on the global market. Here they are, in alphabetical order.  


ActivL artificial disc for disc replacement surgeryImage Credit: AesculapactivL® Artificial Disc

FDA Approved: YES


FDA Indication

The activL Artificial Disc is FDA approved for skeletally mature patients with single-level degenerative disc disease at either L4/L5 or L5/S1 in patients who have failed at least six months of nonoperative care

Patients cannot have more than a grade 1 spondylolisthesis or have bad bone quality as determined by a spine surgeon. Patients may have had previous microdiscectomies and laminectomies and still be considered as candidates for the procedure. The manufacturer has patient resources that provide the full range of indications and contraindications for the device. 

Summary

The activL® Artificial Disc was approved by the U.S. Food and Drug Administration (FDA) in 2015 after it was studied in a head-to-head randomized, controlled trial where safety and effectiveness outcomes between the activL and two other previously FDA approved lumbar discs, including the ProDisc-L, were studied. In this study at the 24-month primary composite endpoint, the activL was found to be 14% more likely to be successful than the control devices (ProDisc-L and Charite). 

Success was primarily driven by the strong maintenance of range of motion outcomes associated with the activL. Importantly, across disc replacements this clinical study found only about a 4% overall device failure rate and extremely good return to work and narcotic utilization outcomes. The activL® Artificial Disc was designed in partnership with two U.S. orthopeadic surgeons backed by the same engineer expertise that had designed ProDisc-L (Aesculap, the activL manufacturer, actually sold ProDisc-L before designing activL). 

The company says that activL moves differently than previous generation lumbar discs. It features anatomically correct rotational and translational motion that more closely mimics the natural, healthy, human spine. In fact, at 5 years, activL patients have 31% more range of motion – potentially because of these design features, which the company calls “Intelligent Motion Technology.” You can read a lot more about the activL device, its design attributes and available clinical evidence through this open access article and through the activL Artificial Disc patient website www.soactivesofast.com/lowback.

What stands out about the activL Artificial Disc?

Sizing. The activL Artificial Disc offers the smallest height disc, ideal for many with small statures, out of any other disc replacement system currently available on the global market. It’s just 8.5 mm tall (also available in 10, 12 and 14 mm for those of us needing that). It also comes in four endplate footprints which your surgeon will size you up for at the beginning of your procedure (S, M, L, XL; 26 mm x 31 mm, 38 mm x 34.5 mm, 30 mm x 39 mm, 33 mm x 40 mm) and lordotic configurations of 6°, 11° and 16°. 

Approach/Insertion

It is inserted through the belly. Like most lumbar disc replacements, the activL is inserted through a direct anterior retroperitoneal procedure. Is this crazy? No. Nearly 13% of low back surgeries done in the U.S. are done through an anterior approach*. Why? Muscle sparing. Anterior surgery is considered to be less invasive and is associated with shorter recovery times. Because midline placement and alignment can be so important in disc replacements, it’s no wonder why surgeons prefer a direct anterior approach for disc replacement insertion. Yes, a small incision will be made in your belly leaving a small scar behind but your spine surgeon typically will use an access surgeon to help with this approach. 

Wear Testing

The wear testing completed on the activL Artificial Disc is aggressive. It was tested out to 100 million cycles (validated to 80 years) and the company found that it wore 16 times less than a hip replacement, seven times less than Charite and six times less than ProDisc-L. 

Endplate Material

The activL Artificial Disc consists of two endplates made of cobalt-chromium metal alloy with a titanium coating and a plastic insert that fits between the two endplates. The plastic insert is flat on the bottom and round on the top and is designed to move as you move during daily activities. 

Fixation

The activL is stabilized in the spine using spiked endplates and will be available in 2019 in the FDA approved keel version for patients with certain anatomies. 

Inlay Design & Fixation

The activL artificial disc inlay is manufactured from ultra?high molecular weight polyethylene. 

Degrees of Freedom & Biomechanics

The artificial disc offers 4 degrees of freedom. The activL’s plastic insert permits motion at the treated level of the spine allowing it to move front to back within the metal endplates but not side to side.



The AxioMed Freedom DiscAxioMed Freedom Disc

FDA Approved: NO


FDA Indications

Not applicable, it has not been approved for use in the United States by the FDA. 

Summary

The Freedom Lumbar Disc (FLD) replaces degenerated lumbar discs using polymer cores designed to mimic the functionality found in healthy human discs. The implant’s core responds to different varying degrees of pressure and loads with the same finesse as the human spine.

Freedom disc was originally designed by physicians at the Cleveland Clinic and has changed hands several times over its history. An FDA clinical trial was initiated on the disc but money trouble for this company means prospective patients do not know the outcomes of this study. It may still be too early to say if the clinical outcomes will be robust enough to allow Freedom Disc to receive FDA approval. There is some speculation that the original owner went bankrupt before they could finish collecting the trial outcomes. Freedom disc is currently broadly marketing in destinations outside of the United States where the regulatory pathway does not demand significant clinical evidence.

The Freedom disc is available in lordotic configurations of 8° and 12° and in three endplate footprints: 26mm, 28mm, and 30mm. 

What stands out about the Freedom Disc?

The designers of the Freedom disc boast that it is a six degree of freedom device offering compression. Unlike earlier generation devices, this may be a biomechanical advantage. Many surgeons speculate that they are eager to see the randomized controlled trial evidence and long-term adjacent segment outcomes.

 

Approach/Insertion

Like its predecessors, Freedom Disc is inserted through a direct anterior approach. According to the manufacturer, the Freedom Disc’s one-piece design simplifies surgical implantation by using a rails and bead-coated titanium endplates keep the device securely in place.

 

Wear Testing

Prothesis durability passed a shelf life of 50 million operations (and 30 million load cycles) without failure. Devices lost an average of 0.07 g weight over 30 million device cycles of wear testing. The parts lost approximately 1/4 of a millimeter in height over 30 million cycles, while the periphery dimension increased by about 3/4 of a millimeter. 30 million cycles is equivalent to about 30 years.

 

Endplate Materials

The Freedom Disc is a one-piece viscoelastic total disc replacement (TDR) consisting of an elastomeric core bonded to titanium retaining plates. Its core material is CarboSil™ TSPU, a silicone polycarbonate urethane thermoplastic elastomer.

 

Fixation

The retaining plates and endcaps are manufactured from titanium alloy and contain features on the bone-interface side to provide both short- and long-term fixation of the device to the vertebral body. End caps are locked into the retaining plates prior to implantation.

Inlay Design

According to the designers, its viscoelastic core made of a polycarbonate-urethane polymer allows the Freedom Disc to maintain natural feeling spinal movement.

 

Degrees of Freedom and Biomechanics

The Freedom Disc is designed to move like a human spine and biomechanical testing shows that the device is stronger than a real human disc. It maintains stability while giving the spine three-dimensional motion.

Axiomed’s Freedom Disc is currently only available outside the U.S. as it awaits FDA approval in the US.

 


Balanced back system for disc replacementBalancedBack

FDA Approved: NO

 

FDA Indications

Not applicable, the device is currently under investigation in the United States.

 

Summary

BalancedBack positions itself as an alternative treatment for fusion or artificial disc replacement (ADR) using total lumbar arthroplasty. The manufacture dubs it, “the first ‘total’ joint for the lumbar spine. The implant’s design—made up of two sides, each of which has a top and bottom component that fixes to the bone similar to the hardware configuration of a spinal fusion—is seen by the manufacturer as the next innovation after artificial discs. Patients undergoing a procedure to receive one of these implants receive it in a posterior approach instead of through the belly like artificial disc replacement. This allows your surgeon to decompress pinched nerves while restoring biomechanical stability to your spine.

 

What stands out about BalancedBack?

Its indication is broader than traditional total disc replacements. BalancedBack’s design replaces the function of the facets and the disc. Though it uses a similar structure to fusion, its screws do not protrude into muscle tissue, which causes pain. Instead, the screws sit embedded into the device. According to the manufacturer, BalancedBack allows for postural correction, stenosis decompression, removal of arthritic facets, and relief of other factors causing muscle irritation and spasm.

 

Insertion

Surgeon completely replaces the worn-out joint-a posterior approach, which theoretically helps to address the leg and back pain.

 

Mean Wear Rate

Not publicly available.

 

Endplate Material

Not publicly available.

 

Fixation

BalancedBack uses the same fixation as the pedicle screw used during fusion procedures to secure the device. The difference being the screw's tails are entirely within the bone and do not protrude.

 

Inlay Design & Fixation

N/A

 

Degrees of Freedom & Biomechanics

N/A

 

BalancedBack is not available in the U.S. (it’s performed by a pair of surgeons in the Cayman Islands). The surgeons cite the environment as part of their holistic approach to treatment and healing for the patient.

 


M6-L Lumbar artificial discM6-L

FDA Approved: NO

 

FDA Indication

The M6-L manufacturer has not indicated that they intend to bring the device to the US market.

 

Summary

The M6-L artificial lumbar disc from Orthofix offers a sleek design that’s based on the feel and function of natural spinal discs. It’s the first of its kind to use a polycarbonate urethan and woven fiber annulus to create an artificial nucleus that models the form and function of its natural counterpart. Its material, two titanium outer plates and a titanium plasma spray, is designed to promote bone growth into the metal plates to lock the disc in place and create long-term stability in the spine. The M6L is available in lordotic configurations of 3°, 6°, 10°, 16°. It offers two implant heights, 10mm and 12mm and 3 footprints (M, L, XL; 27 mm × 35 mm, 30 mm × 39 mm, 33 mm × 44mm)

 

What stands out about the M6L?

The M6-L moves like your natural disc once in the body and warmed up. Its artificial nucleus and annulus provide compressive capabilities and a controlled range of natural motion in all 6 degrees of freedom—side-to-side, up and down, and front-to-back.

 

Insertion

Similar to other devices, the M6L is inserted through a retroperitoneal approach through the belly.

 

Mean Wear Rate

Wear debris analysis to 20 million cycles (less or equal to 20 years):

  • Mass loss: 16.9 ± 12.0mg.
  • An average of an additional 25.9 mg of debris were generated and trapped inside the inside the device. Total device debris was therefore less than 43 mg.


Endplate Material

The M6-L is made of inner and outer titanium endplates coated in titanium plasma spray.

 

Fixation

Keels are used to secure the implant.

 

Inlay Design & Fixation

The M6-L is the only artificial disc made with an artificial nucleus (polycarbonate urethane) and a woven fiber annulus (polyethylene).

 

Degrees of Freedom & Biomechanics

Those with an M6-L artificial disc can expect 6 degrees of freedom (3 translational, 3 rotational) as well as shock absorption and elastic return.

The M6-L is not available in the U.S. and there are no plans by Orthofix to initiate an FDA submission or US clinical trial for approval of the M6-L.

 


LP-ESP artificial discLP-ESP

FDA Approved: NO

 

FDA Indication

Currently it sounds like the folks at FH Orthopaedics, the manufacturer of the LP-ESP do not plan to bring it to the US Market.

 

Summary

The LP-ESP disc mimics the natural lumbar disc allowing your spine to function with the same natural flexibility of its original disc. According to the manufacturer, people recommended for the LP-ESP discs are those who have undergone treatment-resistant lumbar discopathy, those who have gotten lumbar discopathy disease after treatment of a herniated disc, and those who have radiculopathy due to a recurrence of a herniated disc.

 

What stands out about LP-ESP

Its non-keeled design. The endplates are smooth and don’t incorporate jagged keels, which may affect the bone. It’s also made of 99 percent titanium which reduces the risk of allergic reaction. The LP-ESP’s one-piece cohesive interbody spacer provides six full degrees of freedom about the three axes. In addition, the elastic return property provides a potential protection for the posterior facet joints. It is offered in 7°, 9°, 11° lordotic configurations and implant heights of 10 mm and12 mm.

 

Insertion

This one goes in through the belly too.

 

Mean Wear Rate

Residual gap between metal endplates: 0.55 mm after 20 million cycles and 0.78 mm after 40 million cycles. This equates to about twenty to forty years.

 

Endplate Material

The LP-ESP is made of titanium endplates and a hydroxyapatite coating.

 

Fixation

To help secure the device within the spine, the LP-ESP artificial disc endplate incorporates three anterior horizontal spikes ensuring a secure initial fixation.

 

Inlay Design & Fixation

LP-ESP single-piece implant uses an inner core made with a silicone nucleus, and an outer core made with a polycarbonate urethane annulus. Its inlay fixation is located inside the two endplates of the implant.

 

Degrees of Freedom & Biomechanics

The LP-ESP artificial disc has six degrees of freedom with an adaptive center of rotation, improved stability, and shock-absorbing design.

 


prodisc L artificial disc

prodisc L

FDA Approved: Yes

 

FDA Indication

The ProDisc-L is FDA approved for skeletally mature patients with single-level degenerative disc disease at either L3/L4, L4/L5 or L5/S1 in patients who have failed at least six months of nonoperative care. Patients cannot have more than a grade 1 spondylolisthesis or have bad bone quality as determined by a spine surgeon. The manufacturer has patient resources that provide the full range of indications and contraindications for the device.

 

Summary

We like the breadth of evidence available on this disc. With over 200 peer-reviewed studies, ProDisc-L is the best-known and longest studied ADR. It is also the only lumbar disc that has begun the process of studying its performance at multiple levels through an FDA IDE study. However, the company never completed the study or sought FDA approval for this expanded indication. The outcomes for the FDA IDE study at five years are widely available and often referenced.

 

What Stands out about ProDisc-L?

Beyond the level of evidence available for the ProDisc-L for some patient anatomies the ProDisc-L flat endplate design and keel feature make sense to surgeons. The ProDisc-L is offered in two endplate footprints (27 mm x 34.5 mm; 30 mm x 39 mm), two heights (10mm and 12mm) and two lordoctic angle configurations (6° and 11°).

 

Approach and Insertion

The prodisc L requires a multi-step insertion through a midline, mini-open anterior approach. This enables the surgeon clear visualization into the disc space and minimizes exposure and risk of damage to vascular structures. The disc requires that a central channel is chiseled into the vertebral body above and below and then the prosthesis is placed in two steps. First the two endplates are inserted and then the disc space is re-distracted to place the plastic middle.

 

Mean Wear Rate

The ProDisc-L wear characteristics are well understood and tested to the same rigors as the activL Artificial Disc. Surgeons who participated in the ProDisc-L IDE studies in the early 2000s say that their patients continue to do well with very little evidence of wear reported.

 

Endplate Material

The prodisc L implant is composed of three components – two cobalt chrome alloy (CoCrMo) endplates and an ultra-high molecular weight polyethylene (UHMWPE) inlay. The plastic inlay locks into the lower endplate allowing the ball and socket of the upper endplate to create motion. The inlay does not move back and forth once locked in place.

 

Inlay Design & Fixation

The prodisc L artificial disc implant uses keels and lateral spikes to provide secure primary fixation and a plasma-sprayed titanium surface to promote integration when resting on the bone. The central keel design is patented by the manufacturer.

 

Degrees of Freedom & Biomechanics

The prodisc L offers 3 degrees of rotation freedom. This is because the central core is locked in place and does not move. Surgeons refer to this design as fully constrained.



Conclusion

Are you considering artificial disc surgery to solve your lumbar disc condition? If so, ask your surgeon which disc best benefits your existing back condition. While all of these options are available to you, only two are FDA approved for use within the United States. After talking to your surgeon, if you are still struggling with which implant makes sense for you we would recommend you check out these studies:


If you don't have a surgeon or have yet to consult with a surgeon about your back, you can find a surgeon near you or in your geographic region with experience in total disc replacement by visiting our Surgeon Finder to make an appointment with a surgeon who can answer your questions or to seek the opinions of multiple surgeons.


 Any implant manufacturer that wishes to provide additional information about their Disc Replacement should contact us. We would welcome the ability to provide additional clinical evidence, biomechanical testing and product positioning information to help back pain sufferers make more informed decisions about their care. Contact us.


* 13% (Source SmartTrak Data, 2018)

Updated: June 4, 2019

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