It is estimated that more than 175,000 cervical vertebral fusion surgeries are performed each year in the United States. Fusion (stabilization) of spinal vertebrae is an anterior or posterior surgical procedure that has become the “gold standard” for cervical pain management. The surgery usually follows the failure of conservative, non-surgical treatment alternatives, e.g., rest, pharmacologic treatments (anti-inflammatory medication, opioid or non-opioid analgesics, antidepressants), cervical collar, etc.) to achieve pain relief. The surgical goal of a cervical fusion is to abate the patient’s pain caused by the compression of the spinal cord or spinal nerves as a result of vertebral disc herniation, degenerative disc disease that causes spinal instability, or spinal trauma (e.g., whiplash).
The fusion forms a fixed bridge between two or more cervical vertebrae facilitated by the introduction of a bone graft with or without instrumentation (plates, rods, screws, etc.). In recent years the bone graft material could be obtained from the patient (autograft) or taken from a cadaveric donor (allograft). A second type of allograft manufactured from synthetic material has been widely adopted by spine surgeons.
Although the majority (75 to 98%) of cervical spine fusions result in a positive outcome, the surgical procedure is not without controversy. A sizeable number of patient’s reported that following the surgery they experienced prolonged pain at the surgical site and/or at the autograft removal site. This has prompted the recommendation that patient’s considering cervical fusion surgery discuss in detail the risks and benefits of both types of graft acquisition procedures with the surgeon prior to the surgery. Smoking, obesity, osteoporosis, prior back surgery and other patient-related factors have been linked to unsuccessful fusion surgery.
An autograft had historically been a piece of graft bone most commonly taken from the patient’s hip or pelvis. Once removed and shaped, the graft bone is placed between the vertebrae to fuse with vertebral bone and/or packed around the interbody instrumentation that is inserted to insure fusion stabilization. The advantages of an autograft were (1) faster healing due to the graft’s osteoinductive and osteoconductive properties, (2) the autologous bone graft was usually well incorporated into the graft site, and (3) the surgical outcome had been more predictable than when allografts or synthetic bone substitutes are employed.
In 2002 a bioengineered, osteoinductive human protein (rhBMP-2) graft implant was approved by the FDA for spinal fusion surgery. BMP is a growth substance that encourages bone cells to proliferate. BMP was initially used for fusion in all regions of the spine, however, as the use of BMP expanded undesirable side effects in anterior cervical spine surgery were noted. These included hematoma formation in the neck causing painful anterior swelling and respiratory distress as well as compression neurological structures. In some cases these results required longer hospital stays and additional surgery. Many surgeons no longer use BMP for cervical fusion procedures, relying instead on allograft material.
An allograft is graft material obtained from a source outside the patient’s body. The most commonly employed allograft continues to be a section of cadaveric bone obtained from a bone bank. The cadaveric bone material has a negligible risk of disease transmission provided approved preparation procedures have been followed. In recent times bio-compatible cell-based, polymer-based or ceramic-based synthetic bone graft substitutes and demineralized bone matrices (DBMs) have been added to the surgeon’s choice of allograft alternatives.
The primary advantage of the allograft is that the surgeon does not have to perform a second surgery to obtain graft material from the patient. This means that the patient spends less time in the operating room (including less time under general anesthesia), experiences less blood loss, and avoids pain and other possible problems such as infection at the graft incision site.
The disadvantages of using an allograft may include (1) slightly longer recovery times and (2) the possibility that the sterilization process (e.g., demineralization, freeze-drying, gamma radiation, etc.) necessary to prevent the transmission of disease from the donor to the patient has decreased the graft’s osteogenic integrity. This could result in the graft having a diminished potential to incorporate with the patient’s bone. If this event occurs, there is a possibility of a failed fusion and the need for another surgery to correct the problem.
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