Cervical spine fusions have been performed since the 1950s and have achieved good, reproducible clinical results. Anterior cervical fusion is a current standard of care for cervical degenerative disc disease (DDD), and 1-level fusions have predictable results, and are a successful procedure for surgeons and patients. However, fusion by definition eliminates the motion that normally occurs in a spinal segment and, as more levels of the spine are fused, the lack of motion created in the neck may cause additional problems for the patient. With the down classification of cervical cages by the FDA in 2007, patients and surgeons were offered more options for on label treatment of 1-level cervical disc disease. There are not as many options for on label multi-level fusion, and this has led to the need for an alternative on label treatment for patients requiring surgery at one or two levels.
The natural mobility of the neck is what allows us to easily perform many common daily tasks, such as driving, participation in sports (such as swimming), and recreational enjoyment (such as golf, photography, etc.). When a fusion is performed, this natural mobility of the whole neck is altered by removing motion at the surgical level(s). Interestingly, the total motion in the cervical spine can return to pre-operative conditions and, it is theorized that, this compensatory mechanism results in an increase in motion and increased loads on the levels of the spine just above and below the fusion. When multiple levels of the cervical spine are fused and rendered immobile, the functional implications can be noticeable to patients as this motion compensatory mechanism is amplified, which can cause greater impact to their daily life activities. Patients with multi-level fusions are believed to have an accelerated rate of adjacent level degeneration, as the altered motion and stresses at the levels next to the fusion facilitate and amplify the progression of their disease. If true, there is an increased likelihood they will be back for more treatment, potentially additional surgery, at a later time.
The body of evidence for non-fusion alternatives, mainly disc replacement, has grown quite large over the past 10 years. Disc replacement studies have shown a lower rate of reoperation and also a trend towards reduced adjacent level degeneration versus fusion. This is promising for patients. Long term data and improvements in non-fusion alternatives will continue to be a need in cervical surgery, as will the need for providing FDA approved, on-label options for patients and surgeons.
Artificial Cervical Disc Replacement
Artificial cervical disc replacement is a surgical procedure of the neck whereby a degenerated native cervical disc is removed and replaced with a prosthetic device made of biologically compatible metals, plastic and/or ceramics, depending upon the device. Cervical disc replacements are designed to maintain vertebral alignment and allow for normal physiological cervical motion. Therefore, cervical disc replacements are often referred to as motion preservation devices. Motion preservation is achieved by surfaces that articulate with other pivoting or sliding surfaces. There are more than 15 cervical disc replacement devices in the global market today, though only six are approved for commercialization in the United States.
Disc Replacement vs. Spinal Fusion Surgery
Fusion surgery and disc replacement begin the same as the disc is removed and the spinal nerves are decompressed in order to alleviate pain and/or neurologic symptoms. Fusion surgery places a mechanical device made of metal or plastic, along with bone graft material, or other material that promotes bone growth, in the disc space in order to support and grow new bone in place of the removed disc. This eliminates motion of the segment while maintaining normal space between the vertebrae to relieve compression of the neural elements. Benefits are predictable bone growth patterns yielding high fusion rates in the cervical spine, contributing to long-term pain and/or neurological relief. The theorized drawbacks include the loss of segmental motion and the transfer of loads to the adjacent levels above and below the fusion. Healthy discs next to a successful fusion site may degenerate at an accelerated rate. Disc replacement utilizes a motion preservation device that allows the segment to move more similar to a native disc. This re-creation of physiological motion provides the same neurological pain relief of fusion without the healing time required for biological fusion or the potential for increased adjacent level problems.
While fusion is suitable for many indications, including patients with cervical instability, cervical trauma, or longer term degenerative changes, cervical disc replacement, or arthroplasty, may be an alternative for many patients. Disc replacement is generally indicated for patients with arm pain and/or a neurological deficit, sometimes accompanied by neck pain, resulting from an abnormality in the disc space (i.e., herniated disc). It is, of course, very important for patients to have a detailed discussion with their surgeon when considering the best treatment option for them.
Anterior cervical discectomy and fusion (ACDF) has been the standard treatment for cervical degenerative disc disease with a long history of good outcomes. Beginning in the 1950s with the Cloward technique, cylindrical bone dowels were easily placed in the cervical disc space to fill the void, restore, and maintain disc height, and provide biological fusion for a solution to pain relief. This procedure has been modified over time to optimize bone graft options (materials and shapes) coupled with many device options for predictable outcomes.
The initial use of anterior cervical plates came about in cervical trauma surgery in the late 1960s by Dr. Lorenz Böhler in Vienna to provide rigid bone fixation that would allow bone growth and graft healing at a fracture site. This was more popularized in 1980 by Dr. Wolfhard Caspar in the Department of Neurosurgery at the University of Saarland, Germany, with the first-generation trapezoidal cervical plate, described for tumor, trauma, and revision applications. The Caspar plate was known to be very strong and stiff with generous open holes for screw fixation. Screw placement in these early plates required bi-cortical purchase to provide stability, as there was no locking feature for the screw/plate interface.
Anterior cervical plating applications grew over time to cross over from trauma to cervical DDD surgeries. The idea of placing a cervical plate over the interbody graft to protect it during the healing process and provide stability of the operated segment was an attractive proposition. Anterior cervical plating was also seen as a solution for anti-expulsion of the bone graft, as well as antikyphosis of the cervical spine.