Implantable sensors, advanced navigation could be next step for disc replacement

Alan Condon -  

The first artificial disc replacement in the U.S. was performed in 2000, but the technology has come a long way since then, with many surgeons predicting that the procedure will one day overtake spinal fusion as the standard of care in the cervical spine.

Thirteen spine surgeons detail the next big step for cervical disc replacement, including implantable sensors, advanced navigation features when placing an artificial disc and nanotechnology that can monitor the facet joint and adjacent disc pressure.

Ask Spine Surgeons is a weekly series of questions posed to spine surgeons around the country about clinical, business and policy issues affecting spine care. Becker's invites all spine surgeon and specialist responses.

Next week's question: Can you detail a recent spine surgery that you are particularly proud of? What was challenging about the patient's condition? How did you approach the surgery and what was the outcome?

Please send responses to Alan Condon at acondon@beckershealthcare.com by 5 p.m. CDT Wednesday, Aug. 31.

Editor's note: Responses were lightly edited for clarity and length.

Question: Cervical disc replacement has really taken off in recent years, and long-term data continues to impress. What advancements would you like to see in the design and functionality of artificial discs?

Michael Goldsmith, MD. The Centers for Advanced Orthopaedics (Bethesda, Md.): I have been incredibly happy with the results of cervical disc arthroplasty over the last 12-plus years. The key to success with total disc replacement, as with many procedures in spine surgery, is patient selection. Patient selection is so vital, especially since anterior cervical discectomy and fusion is still an excellent alternative in patients with contraindications, and helps to ensure good outcomes with surgery. 

The next step with TDR will be to integrate sensors in the implant that can communicate motion, wear and possible loosening. This information will help alert the patient and the surgeon at an early stage when there may be a problem that warrants a visit to the surgeon.

Adam Kanter, MD. Pickup Family Neurosciences Institute at Hoag Hospital (Orange, Calif.): In the right patient with the right pathology, few treatments provide as much relief and patient satisfaction as artificial disc replacement. My expectation for the future in ADR technology is for the implants to be more imaging friendly and require less of it. Some ADR implants create tremendous artifact that make follow-up imaging with MRI difficult if future issues arise. But what I would really love is if the implant was able to communicate its movement and mechanistic "health" through bluetooth or some other wireless/imageless mechanism. That is the future; more information but requiring less imaging.  

Christian Zimmerman, MD. Saint Alphonsus Medical Group and SAHS Neuroscience Institute (Boise, Idaho): Concerns and ongoing discussions surrounding the potential failures with cervical arthroplasty are centered around errors in patient selection or surgical technique. Patients with advanced spondylosis, osteophytic disease, severe facet arthropathy, osteoporosis, sagittal deformity or preoperative instability remain poor candidates for artificial disc surgery and more prone to resultant complications. Post-operative issues such as heterotopic ossification, adjacent level failure, wear and tear debris, tissue reaction and limitation to just a single level also enter discussions around design and usage. Having placed and removed a number of these devices, future advancements like better end plate insinuation and foraminal distraction, multilevel indicative and cost-contained products might be more advantageous to the market.

Issada Thongtrangan, MD. Microspine (Phoenix): I would like to see a design that can match or restore the patient's sagittal alignment with MRI compatibility. Another novel aspect is the microdevice or chip that will monitor the adjacent disc pressure and facet joint pressure intraoperatively and postoperatively.

John Burleson, MD. Hughston Clinic Orthopaedics (Nashville, Tenn.): I like seeing MRI compatibility. That is probably the biggest change recently as well as the different materials used in that implant. I would also like to be able to determine constraint with a modular component. Right now we can change constraint with different implants, but it might be nice to change out the core of the component before implantation (similar to a constrained hip liner versus a traditional poly) to create an implant specific to that patient's needs at that specific level. 

Vladimir Sinkov, MD. Sinkov Spine Center (Las Vegas): Cervical disc arthroplasty is a very exciting and promising technology. The procedure has very good short- and mid-term published data showing excellent clinical outcomes, quicker recovery, and much lower rates of adjacent segment degeneration and need for reoperation when compared to traditional anterior cervical discectomy and fusion. I believe this procedure will continue becoming more popular as the indications expand. The limitations of the current implants on the market include poor ability to address cervical instability, facet mediated pain, deformity and multilevel disease. The question still remains on how long the devices will last on average and what would be the best way to revise them.  

Poor surgeon and facility reimbursement for cervical disc arthroplasty also remains a challenge for wider adoption. Since disc replacement is more technically difficult to perform than cervical fusion and requires additional training, it would be expected to be reimbursed at a higher level than fusion but the opposite is currently true for Medicare and most private insurers.  

Richard Guyer, MD. Texas Back Institute (Plano): My wish list:

1. Having AI with CT capability to match the best cervical total disc replacement for the patient's anatomy and height.

2. Preoperatively having the ability to match cervical total disc replacement kinematics with the patient's.

3. Custom-made patient-specific endplates.

4. Newer materials other than what is available today to allow some compressibility.

5. Intraoperative navigation to allow perfect placement of the cervical total disc replacement matching the proper axis of rotation of the patient.

Jessica Shellock, MD. Texas Back Institute (Plano): It would be nice to have some additional options with lordotic angles for cases in which we might be able to improve sagittal alignment in the neck, especially in multilevel cases. It would also be great to ultimately see some new designs with new biomaterials that have a compressible core to mimic a "natural" disc. 

Perhaps more importantly from my standpoint is that we need to get broader insurance coverage for scenarios such as hybrid constructs (ADR and fusion in combination) so that we can utilize the benefit of artificial discs in more clinical settings.

Jack E. Zigler MD. Texas Back Institute (Plano): Two things:

1. Improved biomaterials that perform physiologically more like natural healthy discs, with a progressive viscoelastic response.

2. A "fool-proof" system for axial visualization of the disc space in real-time to ensure maximum endplate coverage and reproducible optimal positioning of the implant.

Alexander Satin, MD. Texas Back Institute (Plano): We now have a diverse array of cervical artificial disc replacement devices available for implantation, with more currently undergoing investigation. These devices differ in overall design, degrees of freedom, material, MRI-compatibility, height options, lordosis and range of motion. Surgeon preference and experience often dictate the choice of implant. As we continue to gain a better understanding of in-vivo biomechanics and "behavior," we may eventually be able to select the ideal ADR for each patient. Our recent research suggests that certain patients develop increased motion after undergoing ADR with an unconstrained device, leading to increased rates of adjacent segment degeneration. Perhaps, these patients would be better served with a more constrained implant? Hopefully, we will obtain the knowledge and ability to produce custom ADRs that maximize footprint and possess adjustable properties that produce optimal alignment and motion.

Brian Gantwerker, MD. The Craniospinal Center of Los Angeles: Cervical artificial disc replacement has proven to be an excellent alternative to fusion in many cases. When it comes to young patients with cervical stenosis, large central disc herniations or degenerative disc disease, disc replacement has been shown to be very durable and as good as cervical fusion and also less likely to require further surgery down the road. Cervical disc replacements each have unique characteristics, making it very important to pick the proper mechanical replacement for the patient's particular pathology. What is very exciting, is being able to do two or more levels on selected patients. Using meticulous technique, good outcomes are possible. However, we must also self-police to avoid the inevitable outliers who feel the need to replace multiple levels using thin or questionable indications. The use of CT Spect scans have also been shown to be helpful when investigating the culprit levels to replace.  

Brian Fiani, DO. Weill Cornell Medicine/NewYork-Presbyterian Hospital (New York City): Cervical disc replacement is an excellent alternative to cervical fusion in the right clinical setting. During my six months of neurosurgery at the Naval Medical Center in San Diego, most of the patients were otherwise healthy individuals with an isolated herniated disc, radiculopathy and a desire to "get back on the ship" quickly for their duties. Many cervical disc replacements were performed weekly. The long-term data continues to show that there is a decreased incidence of adjacent segment disease, less dysphagia postoperatively, and quicker return to daily activities and work. Continued studies are needed on the use of cervical disc replacements for three or more adjacent levels. Additional feature advancements I would like to see include navigational placement of the artificial disc in order to ensure that it is placed midline which is an important factor when placing an artificial disc. Navigational technique would reduce radiation, and likely, the operative time.

Chester Donnally, MD. Texas Spine Consultants (Addison): Continuing to find a way to make these implants add lordosis would be exceptional. Another concept that differs with arthroplasty and fusion is that in ACDFs you can put in a cage that also provides some indirect decompression for the foramen. You do not want to place an "oversized" CDA with the current generation of implants.

Francisco Espinosa-BecerraMD. NorthShore Neurological Institute (Arlington Heights, Ill.): I do cervical disc arthroplasty using NuVasive's Simplify Disc. In recent years, the FDA has approved the device for both one-level and two-level cervical total disc replacement. It is the newest disc that is easy to use and has many improved features, which have resulted in improved outcomes for my patients.

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