By 1990, the cervical DDD market was saturated with many styles and choices of anterior cervical plates made by numerous spine device manufactures. Third generation anterior cervical plates featured enhanced locking mechanisms with anti-screw backout capabilities, variable screw angles, load sharing designs (thinner and less stiff), and customized drill guides and instrumentation that streamlined the surgical technique. Anterior cervical plates have enjoyed success, though complications have been noted over time for screw backout or breakage, esophageal irritation (dysphasia), and potentially stress shielding of the graph preventing bone healing.
By the early 2000s, companies began to explore options to place polyether ether ketone (PEEK) cages embedded with bone graft material in the cervical interbody space, and integrated fixation through the cage directly into the vertebral bodies. This alleviated the need for anterior cervical plates for some patients and simplified the overall procedure.
Today there is a mix of anterior cervical plating and stand alone PEEK cervical cages with integrated fixation on the market. While anterior plating is still more widely utilized in the market, we believe that application of stand-alone devices represents a rapidly growing segment.
Anterior cervical procedures account for more than 240,000 surgeries per year in the US. It is anticipated that motion preservation procedures will grow rapidly as more devices become available and new and long term evidence is published. The FDA approval of such devices is the obvious first step, and as more options are provided for on-label use, the increased usage of motion preservation devices is likely.
There are six cervical discs currently approved in the US—three of which were approved between 2007 and 2009, and another two approved by the FDA in 2012 (Globus’ Secure-C, and NuVasive’s PCM). Five of the available cervical discs in the US are approved for 1 level cervical disease only. In late August, LDR, Austin, TX, received approval from the FDA for the Mobi-C cervical disc replacement device, the first and only cervical disc replacement device to receive FDA approval to treat both onelevel and two-level cervical disc disease. (See Figure 1)Differentiating Mobi-C from other artificial cervical discs is its unique mobile bearing core which allows for controlled angulation and translational motion. In addition, it is implanted without a keel that is cut through the adjacent vertebral bodies like many existing discs on the market. The device’s patented mobile bearing core allows for flexion/extension and lateral bending coupled with translation similar to natural cervical motion.
Mechanical and Intrinsic Benefits
Artificial discs provide motion at the operated level, which allows the whole neck to move in a way that is more physiologic. This, compared to fusion, prevents the potential load transfer to adjacent healthy disc levels and represents the largest mechanical benefit of total disc replacement vs. fusion. The fundamental benefit is that artificial disc technology is intended to create an environment that is more natural.
As with hip or knee replacement, motion preservation for the spine is believed by many to provide a more natural surgical solution. And by maintaining motion, it is hoped that there will be a decreased likelihood, or a decreased rate of, degeneration at levels adjacent to the surgery.
Published clinical results for cervical disc replacement have shown:
- Lower reoperation rates for cervical disc replacement as compared to fusion
- Sustained motion at operated levels
- Trends toward lower rates of adjacent level degeneration
Many of the surgical steps to implant a cervical artificial disc are the same as performing an anterior cervical fusion. So the good news is that most of the surgical procedure is familiar to surgeons. However, there are specific considerations for an artificial disc regarding placement and sizing, and patient indications must be respected for good outcomes. We believe that many surgeons will be open to learning about artificial discs as second generation discs become available, and the quantity of consistent data to support good clinical outcomes is compelling.
The Challenge of Two-Level Cervical Discs
Why aren’t there more two-level discs on the market? This is a combination of factors. To begin, you must start with the design of the devices themselves. Some of the currently approved devices incorporate features that may make them less attractive for two-level applications. So in order to pursue two-level approval, you must start with a device specifically designed for both 1 and 2-level use. For example, the keels associated with many devices make them difficult to implant on two adjacent levels without compromising the vertebra in between the two keel cuts. If a device with anterior screw/flanges is used, the anterior vertebral body real estate may not accommodate so much hardware.
LDR is one of only two companies to have completed enrollment of a two-level cervical disc replacement study, and was the first to receive approval. In order to market a cervical disc device for two-level applications in the US, it is necessary to complete an investigational device exemption study and gain approval through the premarket approval process. This is a very arduous process and few device manufactures to date have made the necessary investments to study this large patient population.
The Mobi-C cervical artificial disc was first implanted in 2004 in Europe. To date, it has been implanted in more than 17,000 cases outside the US, in countries around the world. The device entered an IDE study in 2006, with approximately 600 patients enrolled in the US to study 1- and 2-level disc replacement and was recently approved by the FDA.
Information in this article was supplied by Joe Ross, Executive Vice President of Global Marketing, LDR Spine, Austin, TX. For more information, Click Here.