Spinal fusion has become a very common surgical procedure in the United States over the past 10 years. There are many diagnoses that range from fractures of the spine to severe degenerative disc disease that prevent patients from being able to stand or walk are best treated with a surgical remedy. This article is intended to provide a basic review of the many spinal fusion options that are available. It is best to talk to a fellowship-trained spine surgeon who will be able to give you a complete picture of all of the devices available that are recognized for quality and reliability or to help you rule out those that are not recommended.
As the number of spinal fusions has increased, the variety of procedures and hardware alternatives that are available has also increased. It may be easier to understand why there are so many types of fusions if you consider how fractures need to be fixed with fusion. With broken bones, there is usually little question about the wisdom of providing casts or plates and screws to stabilize bones that need to be realigned or stabilized. Spinal fusion provides the same stability for the spine as is used for other fractured bones. What is a spinal fusion? Screws and rods in the spine are used to keep bones from moving as the bone graft that is placed allows the stabilized bones to form a connection across a previously mobile disc space. The growth of bone between 2 previously mobile bones is called fusion.
Standard fusion technique: Initially, fusion of the vertebral bones was done by laying bone graft between the bones, to provide a scaffolding across which the native bone cells could grow. As the patient’s bone cells move across the bone graft, they are able to incorporate the bone graft into the patient’s own bone structure, forming a complete connection called a fusion. Bone graft is of primary importance in allowing the vertebral bones to fuse across a previously mobile segment. Studies of patient’s with fusions done with bone graft alone have shown a relatively good rate of incorporation when patients are placed in back braces for 3 months or more. Because of the inconvenience and discomfort of the bracing, pedicle screws and rods have been added to provide an internal support that obviates the need for external supports. Internal screws and rods have increased successful fusion rates, as well as allowed patients to become mobile very quickly after the spinal fusion.
Interbody fusion cages: As the skill of the surgeon’s has grown when applying screws and rods to the spine, we have, in turn, looked for better ways to gain improved results. Now, we are able to put bone graft around the back of the spine, as well as into the disc spaces. With these improved grafting methods, we are able to safely access the lumbar disc from the back of the spine. Adding bone graft to the disc increases the surface area for healing and should improve the overall success rate of the spinal fusion. Interbody grafting can be done from several different approaches, as access to the disc space can be achieved from multiple directions.
XLIF: This acronym stands for extreme lateral interbody fusion. XLIF is a newer device designed to provide a carrier for bone graft and support to the disc space. It is placed through an incision on the patient’s flank. By making an incision on the patient’s side, the abdominal contents can be moved out of the way for a good view of the spine. Unfortunately, there are some significant nerves in the front of the spine that are very sensitive to being moved. This type of access to the spine can lead to weakness in one leg because of the sensitivity of these nerves. At this time, there are no long-term studies that demonstrate success of this procedure.
AxiaLif: This is another fusion device that has received some attention, due to its being touted as the “least invasive spine fusion”. This device is placed across the lowest disc space by access from the front of the sacrum (a large, triangular bone at the base of the spine, inserted like a wedge between the two hip bones). By placing instruments through a small incision near the rectum towards the spine, the disc is accessed through a series of cannulas (hollow surgical tubes) and drills. This allows the disc material to be removed from the disc space. After the disc material is removed, bone grafting can be placed into the hole that is created. This disc space is then supported by a tapered screw placed into the bones. So far, this device has had minimal post-surgical study and is most likely best done in conjunction with standard screw and rod fusion techniques.
Flexible Rods: There has been some recent excitement around rod and screw systems that are so-called “non-fusion” fusion devices. This confusing name infers that, although the intent of the screws and rods is for the bones to not move, these devices are designed to allow some movement. As was discussed earlier in this article, fusion is the solid connection of bones that had previously moved. The idea of these flexible rods is to provide “enough” stability to allow the bones to fuse together, but not enough to change the forces in the spine. This is termed a “soft-fusion”. At this point, there is no consensus as to how much or how little support is needed to achieve this goal. It is known that current screw and rod systems provide enough support to allow a fusion to occur while providing complete immobility of the vertebrae. Other than this complete connection, the amount of support less than complete immobility has not been defined and at this point is still under investigation.
Disc Replacement: Disc replacement was developed as an alternative to fusion and is suggested for those discs that have ruptured, but in which the bone structure is still good. If only the disc has gone bad, removal of the disc leaves a space that we normally fill with bone graft to promote fusion in the neck or lower back. With the development of the disc replacement, the space that is left from disc removal can be filled with a device that allows motion, rather than fusion. This is a complete reversal in the approach to disc removal; from complete immobility to complete mobility. Disc replacement is intended to maintain the motion in the spine. This reconstruction of the spine should maintain the forces across the discs in the spine to prevent the other discs from deteriorating any more rapidly than their normal degenerative process. Disc replacement in the lumbar spine has met with some success in well-selected patients. It has not been a panacea for all patients with low back pain or degenerative disc disease. Disc replacement in the cervical spine has had good success, as most neck fusions are done for bad discs with the bones being in good condition.
Improved training, including advanced specialty training in fellowship programs, as well as improved implants, has decreased most surgical procedure times to 2 hours or less. Historically, older techniques have been known to take 4-6 hours for the operation alone. By decreasing operative times, surgeons have seen decreased complications from the anesthesia, as well as decreased risks of infection and blood loss. Most surgeries under 2 hours will not require a blood transfusion.
A well-informed patient, who understands the benefits and the risks of their surgery, can fully participate in the choices that need to be made about their surgery. If you have been told that you need a spine fusion, ask questions and do your research. It is appropriate to ask your surgeon about their experience performing spinal fusions, how many of the fusion procedures they perform, how long the operation will take and the likelihood of needing a blood transfusion. Selecting a well-qualified surgeon can help ensure the best outcome for you and the success of your spinal fusion.