Cervical Total Disc Arthroplasty (TDR)
Cervical arthroplasty was first developed in 1966. At the time, ACDF was gaining popularity due to reports of great clinical success. The interest in cervical arthroplasty arose because it offered patients a movement-preserving procedure in comparison to the ACDF. However, they were largely abandoned shortly thereafter due to high complication rates experienced with early designs.
It wasn’t until the 1980s and 1990s that this procedure began gaining popularity in Europe after more advanced modifications were made, resulting in improved patient outcomes. In 2002, first reports on modern cervical ADR appeared with the premise that it would decrease or prevent adjacent segment disease by maintaining motion. Since 2010, there have been several randomized controlled trials published that demonstrate superiority to cervical fusion with regards to reoperation rate and quicker return to work in comparison to ACDF. Furthermore, patients are immobilized in a cervical collar for only 1 week postoperatively.
Overall complication rate has been shown to be equivalent or better than ACDF, although there are unique complications to be mindful of. The most common complication reported is heterotopic ossification, which abnormal bone growth around the implant. This may lead to loss of motion in some patients.
Although it is a common complication of the procedure occurring in 50% of patients over a ten-year period, it is regarded by some as a rather insignificant complication considering the alternative procedure (ACDF) completely eliminates motion from the start. Proponents argue that in the subset of patients who would develop HO, it is better to give them 5-, 10-, 15-years of preserved motion before the development of HO limits or completely eliminates motion.
The most fearful complication of TDR is neurological injury from component malposition or migration; however, this is rare. Considering this is an artificial joint, there also is the risk for possible revision of components secondary to wear. It is also important to remember this is a relatively new procedure and long-term outcome studies are still not available.
This procedure is FDA approved for skeletally mature adults (age 22-60 years old) for reconstruction of a single disc from C3-C7 vertebrae for intractable symptomatic cervical disk disease (SCDD). It is recommended that this technology be reserved for those who have failed at least six weeks of nonoperative treatment.
This technology should not be used for any patient with an active infection, significant osteoporosis (defined as DEXA bone density measured T-score less than or equal to -2.5), allergy or sensitivity to the implant material (cobalt, chromium, molybdenum, polyethylene, titanium), severe cervical spondylosis (loss of disc height >50% or an absence of motion <2 degrees), or instability. This procedure can be used below prior fusions, avoiding the need to remove a plate or minimizing esophageal or RLN manipulation.
Cervical disc arthroplasty is performed through an anterior approach with a 3-5cm horizontal incision made on one side of the neck. The vertebral segment of diseased disc is then exposed and removed, along with any osteophytes or other causes of nerve compression. Once decompression is complete, the disc replacement device is sized and placed into the appropriate position between the vertebra with the aid of live xray (fluoroscopy). Once in place, the wound is closed. Patients often are able to go home the same day
Cervical Spine Surgery
Initial treatment of SCDD involves a trial of non-operative management usually for 6-12 weeks, with physical therapy, medications and occasionally injections as the mainstay of treatment. If the symptoms fail to resolve or if the neurological symptoms are severe and/or progressive, then surgical management is indicated. Depending on the cause of symptomatic cervical disc disease, various surgical procedures may be used.
Patients that have a herniated disc isolated to only one side may be candidates for posterior discectomy (AKA lamino-foraminotomy), which is performed from the back of the neck and involves removing a small section of bone. This creates more space for the nerves, relieving the pressure that is causing the symptoms. However, the most common procedure both historically as well as in today’s practice for symptomatic cervical disc disease is anterior cervical discectomy and fusion (ACDF).
This involves accessing the spine through the front of the neck, removing the disrupted disc entirely, filling the void with a space-occupying substitute (e.g. bone graft, metal cage, medical grade plastic), and then fusing the two adjacent vertebrae together. Although this eliminates any movement between the two adjacent vertebral bodies thus eliminating pain caused by bone-on-bone friction, there are some drawbacks. By eliminating movement between the vertebrae, it is thought that this may potentiate degeneration of the vertebral bodies above and below the fusion as a result of the increased torque applied to these respective joints.
Fusing the two vertebrae together requires a metal plate applied to the front of the bones that can often result in esophageal irritation, although this often times transient. There is also risk for failure of the bones to fuse together (non-union), necessitating further operative management. Following the procedure, patients require immobilization in a cervical collar for 6wks to help mitigate the risk of non-union. Overall, the complication rate of this procedure is low, which is why it is the “gold standard” in today’s practice.
Although this procedure has decades of clinical follow up demonstrating good long-term outcome, there has been a shift in interest to procedures that are motion-preserving. A novel technique that is has gained popularity in last several years is Total Disc Replacement/Arthroplasty, which creates an artificial motion-preserving joint between the two bones.
Symptomatic Cervical Disc Disease
Symptomatic cervical disc disease is a condition that results from damage and degeneration of the cushion (disc) between the bones (vertebrae) of the neck (cervical spine). When the disc between the bones is damaged or deteriorated, the bones can rub against one another causing significant pain.
Damage to the intervertebral discs can also be an independent source of pain. When the structural integrity of the disc is violated, part of it may protrude (i.e. herniates), which can compress the spinal cord directly, or may compress the nerves exiting the spinal cord (i.e. peripheral nerves) that provide sensation and muscle function in the arms/shoulders/neck in the case of the cervical spine.
Bone spurs (osteophytes) can develop in response to prolonged bone-on-bone contact, which can also be a source of nerve compression. When compression of the peripheral nerves occurs, this often manifests most prominently as unilateral pain in upper extremities/neck that may or may not radiate down the respective arm. Compression of peripheral nerves, referred to as cervical radiculopathy, may also cause weakness in certain muscle groups of the upper extremity.
When the spinal cord is compressed directly, this is referred to as cervical myelopathy, which typically manifests more as weakness as opposed to pain bilaterally, with spasticity and rigidity common as well. All the above can be part of Symptomatic Cervical Disc Disease (SCDD).
The Prodisc-C Total Disc Replacement is one the most commonly used technologies for cervical disc replacement. It is intended to significantly reduce pain through the removal of the diseased disc while restoring disc height and providing the potential for motion similar to native anatomic kinematics. It is a modular implant, meaning that there are numerous components as opposed to a single rigid construct. It consists of two metal endplates (composed of cobalt chromium molybdenum alloy, CoCrMo) that are placed on the superior and inferior borders of the two vertebral bodies with a medical grade plastic (ultra-high molecular weight polyethylene) that is between the plates.
The polyethylene insert is convex in shape which articulates with the polished concave bearing surface of superior endplate. These together form a ball and socket design, allowing for the preservation of motion with unconstrained axial rotation, and 20 degrees of motion in both flexion and extension. Both of the metal plates have a central keel that anchors into the vertebral bodies providing secure primary fixation.
These central keels are similar in concept to the shape of a sailboat and how they are able to remain stable in hazardous conditions. The keels have a superficial layer of titanium porous coating, which aids in long-term fixation. There are six sizes of endplate footprints and three different polyethylene height options, allowing for a total of 18 possible configurations to appropriately fit nearly any specific patient dimensions.