Cervical arthroplasty, or artificial cervical disc replacement (CDR), is an advanced surgical procedure aimed at alleviating neck pain and restoring mobility by replacing damaged or degenerated cervical discs with a mechanical prosthesis. This procedure has gained popularity as an alternative to the traditional anterior cervical discectomy and fusion (ACDF), especially for patients seeking to maintain motion in their cervical spine.
Terminology
CDR, ADR-C, TDR-C are used to refer to artificial disc replacement surgery in the cervical spine (neck region).
When to Consider CDR
Cervical arthroplasty is typically considered when nonoperative treatments for neck pain and associated symptoms have failed for greater than 6 weeks. A thorough evaluation by a spine specialist, including imaging studies like x-rays, MRI, or CT scans, is essential to determine if cervical arthroplasty is appropriate. Indications for cervical arthroplasty include:
- Neurological Symptoms: Numbness, tingling, or weakness in the arms or hands due to nerve compression.
- Persistent Pain: Chronic neck pain that does not respond to physical therapy, medications, or other non-surgical treatments.
- Spinal Cord Compression: Symptoms of myelopathy, such as difficulty walking, balance issues, or hand dexterity problems.
Basics & Benefits of the CDR Procedure
The CDR procedure involves removing the damaged cervical disc and replacing it with an artificial disc implant. This surgery is performed under general anesthesia and typically involves the following steps:
- Incision: A small incision is made in the front of the neck.
- Disc Removal: The damaged disc is carefully removed to decompress and free the spinal cord and nerve roots from pressure due to degenerating disc tissues or bone.
- Implant Placement: An artificial disc, designed to mimic the natural movement of a healthy disc, is inserted into the disc space after vertebral endplates are prepared to receive it.
- Closure: The incision is closed, and the patient is taken to the recovery room.
The primary benefit of CDR over ACDF is the preservation of motion at the operated level, which may reduce the risk of adjacent segment degeneration, a condition where discs above or below the surgical site deteriorate over time. Also, a shorter healing time is required for CDR than ACDF which requires time to achieve bony union of vertebrae across the entire disc space.
Implant Differences and FDA Approvals
Artificial cervical discs vary in materials and design. Device surface endplates are sprayed with titanium plasma to aid with integration to adjacent cervical vertebral bony endplates.
The most common materials used are:
- Medical-grade metal alloys (such as titanium or cobalt-chromium)
- Polyethylene (a durable plastic)
- Medical grade thermoplastic with a zirconia-toughened alumina ceramic core.
Implant designs can differ on:
- The type of articulation, ranging from ball-and-socket to more constrained designs (movement in one or more directions)
- The material properties, where less dense metals or non-metals yield less visual obstruction on x-rays, MRIs, and CTs.
Several artificial cervical discs have received FDA approval for use in the United States. Notable examples include:
- Prodisc C: One of the first artificial discs approved by the FDA, composed of two components featuring a ball-and-socket design, with a keel on the superior and inferior endplate to allow bone growth from endplates to secure the device allowing natural motion. Components are Cobalt chrome alloy and ultra-high molecular weight polyethylene inlay. It is used to replace a disc between C3 to C7. FDA approval December 2007.
- Mobi-C: Approved for use at one or two levels of disc, offering a mobile core design that allows for a range of controlled motion. It has a keelless design which allows easier insertion. It is also the first device approved for one- and two-disc levels of the cervical spine. FDA approval August 2013.
- Prestige LP: Made of a metal-on-metal design, it is made with a titanium carbide alloy that provides improved MRI visualization over cobalt chrome alloy. It is a two-piece ball and trough configuration. It is approved for one- and two-disc levels of the cervical spine. FDA approval August 2013.
- M6-C: Is the only one-piece disc replacement with a compliant polycarbonate urethane (PCU) polymer core between two titanium endplates and a PCU and fiber-based sheath which mimics the natural disc structure. The endplates are coated with titanium plasma spray. This device provides progressive resistance to motion in all six degrees of freedom. It is approved for replacement for one disc level in the cervical spine between C3 to C7. FDA approval February 2019.
- Simplify Disc: Consists of thermoplastic polymer endplates and a ceramic core. It provides a low-profile option for patients with specific anatomical needs. Due to its use of non-metallic components, it has the advantage of allowing visibility of the spine on x-ray and MRI without metallic obstruction. It is approved for replacement at one or two discs of the cervical spine between C3 to C7. FDA approval April 2021.
Inclusion and Exclusion Criteria
When a spine surgeon is considering cervical arthroplasty, they must determine if the procedure is right for each patient. They do this by considering the inclusion criteria used in the FDA clinical trials for each device. These criteria include:
- Musculoskeletal adult older than age 18
- Symptomatic cervical disc disease at one or two levels
- No previous anterior cervical spine surgery at the intended levels
Exclusion criteria include:
- Severe osteoporosis or other bone diseases.
- Active infection or systemic disease.
- Multilevel cervical disc disease beyond two levels.
Off-Label Uses and Hybrid Constructs
While cervical arthroplasty is primarily approved for one or two levels, there are instances where off label use or other hybrid constructs may be considered. Off-label use involves using the artificial disc in ways not specifically approved by the FDA, such as in patients with more than two affected cervical disc levels. Hybrid constructs combine cervical arthroplasty with ACDF, providing stability and motion preservation specifically targeted at different segments of the cervical spine to optimize motion, stability, and spinal alignment. Spine surgeons who are experts in CDR have experience in off-label uses.
Conclusion
Cervical arthroplasty offers a promising alternative to traditional fusion surgeries for patients with cervical disc disease. By preserving motion and potentially reducing the risk of adjacent segment degeneration, CDR can provide significant relief and improve quality of life for many patients. A thorough evaluation by a spine specialist trained in CDR is crucial to determine candidacy and ensure the best possible outcomes from this advanced surgical technique. As technology and surgical techniques continue to evolve, cervical arthroplasty may become an increasingly preferred option for treating degenerative disc based cervical spine disorders.
