By now most people are familiar with joint replacement surgery to address end-stage degenerative joint disease. With over 7 million people in the U.S. living with a hip or knee replacement, it is likely you know someone who has had one. From a patient satisfaction standpoint, joint replacements are some of the most successful elective orthopedic procedures being performed. Now a similar approach is being employed to address degenerative disc disease in the cervical spine (neck) in the form of disc replacement surgery. This technology, and its increasing adoption among spine surgeons, is a major evolution in cervical spine surgery.
Generally speaking, spine surgeons address two types of pathology: nerve impingement and spinal instability. Regarding nerve compression, this problem arises as the result of disc degeneration, bone spur formation and subsequent pathologic pressure on nerves. In the cervical spine, degenerative changes often result in compression of the spinal cord and nerve roots. Affected patients present with neck pain and radiating shoulder and arm pain. When symptoms persist despite physical therapy, oral anti-inflammatories, activity modification and sometimes epidural steroid injections, they are considered for surgery. In the cervical spine, the most common procedure to relieve nerve compression is anterior cervical discectomy and fusion (ACDF). ACDF is the standard procedure for cervical disc disease that has historically yielded very good results.
Many patients when faced with a potential spinal fusion express concern about how their neck will feel after surgery. Chief among them is postoperative range of motion. Patients are counseled that range of motion will be somewhat less than preoperatively but will not affect function and ability to perform activities of daily living. More importantly, following successful surgery they can expect improved neck pain and resolution of arm pain. Despite the generally good results of ACDF, many patients have their reservations about undergoing surgery.
Another concern for both patients and surgeons is the potential need for further surgery. As any surgeon will tell you, nothing tempers a patient’s satisfaction with their surgery like the possibility of additional surgery. Following ACDF, there are two complications that can potentially lead to reoperation: failure of the fusion to successfully heal and clinically significant degeneration of an adjacent disc level. Failure of fusion is determined in the first few months after fusion surgery. It is during this time that the bone graft is incorporated into the healing fusion between vertebral bodies at which surgery is performed. Occasionally this event does not occur leading to a condition called pseudarthrosis. Symptoms of pseudarthrosis include worsening neck pain and recurrence of radiating shoulder and arm pain. When this occurs, additional surgery may be required. By comparison, adjacent level disc degeneration occurs months to years after a fusion operation. It is the result of increased load transfer to the discs flanking the fused levels. In turn, the disc experiences accelerated degeneration and may lead to additional surgery when symptomatic.
Cervical disc replacement was developed in large part to address the challenges of cervical fusion. The procedure allows for decompression of neural elements while avoiding decreased postoperative motion of the operated level. The indications for cervical disc replacement and cervical discectomy and fusion (ACDF) are similar. Surgery is reserved for patients who have significant symptoms referable to the degenerated level based on history and examination, those who have a neurologic deficit such as weakness, and attempted appropriate nonsurgical management for at least six weeks.
ACDF vs. Cervical Disc Replacement
Anterior cervical discectomy and fusion and cervical disc replacement are performed with the patient supine under general anesthesia. An incision is made on the front of the neck measuring approximately an inch. Next, a surgical dissection is performed down to the spine taking a path between the longitudinal structures of the anterior neck. The degenerated disc is removed in its entirety. At the backside of the disk, compressive bone spurs and disc herniations are removed, completing the neural decompression. A bone graft is placed in the intervertebral space restoring appropriate spacing between the vertebrae. Finally, a plate is affixed to the vertebrae anteriorly to increase the likelihood of successful fusion. Similarly, cervical disc replacement involves placing the device in the disc space. The device typically has two metal plates that contact the vertebral endplates and have a bearing surface between the two. The prosthesis mimics the normal motion of a healthy disc including flexion, extension, rotation and lateral tilt. Over time, there will be bony on growth onto the roughened outer surfaces of the metal plates further stabilizing the device.
Cervical disc replacement avoids many of the pitfalls associated with ACDF. As expected, cervical range of motion is maintained. Using a motion preserving approach avoids concerns over failed fusion. This is especially so when treating patients with known risk factors for pseudarthrosis like diabetes mellitus and smoking. Of course, these conditions should be optimized before surgery, but their presences make cervical disc replacement a more appealing surgical solution. Finally, there is a lower adjacent level reoperation rate in both one and two-level surgeries when compared to fusion. This is consistent with lesser degrees of radiologic disc degeneration seen in disc replacement patients. However, cervical disc replacement is not without its limitations, the most significant being FDA clearance for one and two-level disc replacements only. For pathology involving three or more levels, ACDF or posterior-based surgery must be considered.
The historical standard of care for cervical disc disease has been ACDF since the procedure was developed over 60 years ago. Growing clinical data on current disc replacement surgery challenges ACDF’s designation as “standard of care” with superior results in various measures such as reoperation rate, adjacent level degeneration, complication rate, pain scores, and range of motion.
By Richard Rhim, MD
Richard Rhim, MD is a board certified, fellowship trained spine surgeon at Active Orthopedics and Sports Medicine. He is on staff at Hackensack University Medical Center, HackensackUMC at Pascack Valley and HackensackUMC at Mountainside. Visit www.activeorthopedic.com for more information.