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Advancements in Spine Surgery

The future is bright for new, improved methods of spinal surgery. Other technological and biological advances are on the horizon that will work in concert with minimally invasive techniques. Several of these, such as computer-assisted image-guided technology, bio-resorbable, flexible and radiolucent spinal implants, and genetic-engineering of disc tissue, bone fusion, vertebral bone, and other steps forward, are worthy of discussion.

Spinal Navigation Technology
Conventional surgery of the spine often involves taking an x-ray during the procedure to confirm the location of the spine or to confirm satisfactory placement of spinal implants (e.g. screws, rods, hooks, plates). Often, surgeons use "live" x-rays during surgery (called fluoroscopy, floor-ah-sko-pee) to obtain this information.

In the past decade, great advances have been made that has taken navigation of the spine (or localization) to a new height. Also known as "computer-assisted, image-guidance," navigation technology is advancing at a rapid rate. More powerful and elegant than simple x-ray technology, spinal navigation technology uses a computer and radiographic studies (x-rays) of the patient to allow the surgeon to know precisely where he/she is at all times.

Spinal navigation technology enables the surgeon to more accurately place spinal instrumentation, perform decompression (e.g. eliminate pressure on nerves), remove tumors, and other tasks. Three-dimensional models of a patient's own spine appear on a computer screen with virtual representations of real surgical instruments that the surgeons have in their hand. Surgeries can even be planned 'virtually' on the computer before a patient even goes to sleep under anesthesia. For example, screw diameter, length, and other measurements can be made with greater accuracy.

The future of spinal navigation is exciting. Rather than send a patient for an preoperative CT or MRI scan, in the future surgeons will be able to obtain images in the operating room that can instantly create computer models of the patient's spine. These models can be used to help navigate the spine during surgery. Intraoperative CT, MRI, and fluoroscopy-based CT offer great potential. The end result is enabling the surgeon to visually "travel" in and out of a patient's spine on computer, thereby allowing them to see things that the human eye cannot during a typical surgery. As spinal navigation technology advances, newer minimally invasive techniques will become available.

Future Biomaterials for Spinal Implants

Great success has been achieved thus far using cages, rods, screws, hooks, wires, plates, bolts, and other types of spinal implants made from stainless steel and (more recently) titanium metal. The great advantage of titanium is that it is allows for better CT and MRI imaging to be performed after implantation with little interference. Stainless steel causes significant "blurring" of CT and MRI images.

Bone Graft
Other types of materials used in spinal surgery include bone graft. Bone is either harvested from the patient's own body (autologous bone) or bone from a bone bank can be used. Bone bank bone (allograft) comes from cadavers and is commercially processed for transplantation into patients. One problem is bone taken from the patient's pelvic bone (ileum) can cause chronic pain; the other is the supply of cadaver bone can be limited.

Bone Morphogenetic Proteins (BMP)
Molecular biological advances will tie in with these navigational and biomaterial advances. Very soon, genetically-engineered proteins called Bone Morphogenetic Proteins (BMP) will be commercially available for bone fusion surgery. This will likely eliminate the need for either autologous or allograft bone use and all of the potential morbidity and limitations inherent in these grafts. BMP can be placed inside a collagen (protein) sponge or other ceramic-type implants and used instead of bone in areas of desired fusion (e.g. disc space, backside of the spine). Thus, in the future, we may be using biodegradable spacers or "fusion carriers" that house BMP, allow for a solid fusion, and then dissolve away themselves leaving only fusion bone behind.

Ceramic and Carbon Fiber
Other materials have been used as carriers of bone graft or vertebral body replacements such as ceramic and carbon fiber. Carbon fiber is radiolucent, which means that implants made of this material do not show up on x-ray. This has the advantage of allowing the bone fusion to be better seen. Future developments will bring even greater advances.

Plastics and Polymers
Because of the potential morbidity of using a patient's own bone (autologous bone) and the limited supply of cadaveric bone, attention has been directed to developing newer materials to serve as spacers and conduits for bone graft material. Other forms of plastic are being developed such as polyether ketone combinations that will be radiolucent yet provide strength and support.

Polylactic Acid (PLA) polymers are also being developed that can actually biodegrade over time. In other words, the PLA will do its job in holding bone graft material and providing support long enough for a fusion to take place, and then it slowly dissolves (hydrolyzes) away after a year or so. Still other materials are being developed that would allow some flexibility and dynamism in a spinal implant. There is some agreement that certain spinal implants may be too rigid and more natural, flexible substances may be a better substrate from which implants could be made.

Disc Replacement or Disc Regeneration
In the future, disc replacement or regeneration may replace the role of fusion in some patients. Though fusion will likely always be a very useful form of treatment in many patients, there may be some patients that will benefit from an implantable artificial mechanical disc. Several forms of artificial disc implants have been used in Europe and are currently being tested in clinical trials in the United States.

The theoretical advantage is that artificial disc replacement will result in improved pain and function with maintenance of some motion at a disc space that otherwise may have been fused solidly by more conventional techniques. Other forms of disc replacement may involve re-establishing the inner nucleus of the disc only with a gel-like material and utilizing the natural anular lining of the disc to contain it (without a metallic component).

Equally as exciting is the possibility that genetically-engineered cells may be surgically implanted or injected into a degenerated disc, allowing for regeneration of disc material that can serve as a shock absorber like the disc we are all born with. There is some experience already with the use of engineered cells in reproducing knee cartilage, so the possibility of use in the spine is real.

Great advances in just the past decade have allowed physicians to treat spinal disorders more effectively. Further advances in biomaterial development, computer-assisted image-guided technology, molecular biology of bone and disc will all be integrated together to develop very powerful techniques for treating spinal disorders. It is this integration of emerging technology and biological advances that will result in smaller incisions, less trauma to normal tissues, faster healing time, equivalent or better relief from pain and neurological problems, and quicker return to functional status.

This article is an excerpt from the book Save Your Aching Back and Neck: A Patient’s Guide, edited by Dr. Stewart Eidelson.

Updated on: 09/17/10
Technological advances in the spine field have been rapid. Since this article was published, BMP (rhBMP-2) received clearance from the United States Food and Drug Administration (FDA) for specific uses. In addition, in October 2004, the FDA approved the CHARITÉ™ Artificial Disc (DePuy Spine, Inc.). Consult your surgeon to learn if you are a candidate.