Minimally Invasive Spine Surgery

1. Overview
2. Non-fusion Technologies
3. Computerized Image Guidance
4. Biological Bone Growth Enhancers/Bone Growth Factors
5. Other Advances
6. The Future Of Minimally Invasive Surgery

Overview

Minimally invasive surgery is a name given to wide a range of procedures with a common goal: treatment that is less traumatic to the patient and that allows a faster return to a normal lifestyle and activities. In surgery of the spine, three main factors are contributing to a rapid proliferation of options for patients who once faced more extensive open surgeries and a prolonged recovery time.

The use of non-fusion technologies, intra-operative computerized image guidance, and bone morphogenic proteins are changing the face of many spine surgeries at institutions like the Hospital for Special Surgery (HSS). Used independently, or in combination, these developments can mean:

• smaller surgical incisions
• decreased operative time
• avoiding or minimizing the need to cut through muscle
• reduced loss of blood
• reduced scarring
• a shorter hospitalization
• a more rapid healing time

Non-fusion Technologies

Traditionally, surgical treatment for many injuries and diseases of the spine meant a large open incision, a fusion (or permanent joining together of bones) and a lengthy recovery period. Non-fusion technologies are replacing that scenario, as in the case of degenerative disc disease, in which the normal discs in the spine become thinner and weaker. As the cushioning effect is lost, the patient experiences pain and stiffness at the site of the damaged disc or discs. Fortunately, only about 20% of cases require surgical treatment, which, until recently, was fusion of the affected vertebrae (the bones surrounding the disc.) By eliminating motion, the surgeon eliminated the patient's pain.

X-ray of a 360 degree fusion with allograft and pedicle screws.

Today, a group of patients at HSS are among the first to benefit from spinal disc replacement, a procedure in which the affected disc is removed and replaced by a prosthesis made of metal and plastic. Frank P. Cammisa, MD Chief of the Spine Service is the primary investigator in a multi-center clinical trial that is comparing the efficacy and safety of these implants versus traditional fusion surgery. "In order to replace a damaged disc, the orthopaedic surgeon makes a small incision in the lower abdomen. With the help of special retractors, small devices to provide lighting, and video images, the prosthesis is put in place without disturbing the abdominal organs," explains Dr. Cammisa.

Photo of Prosthetic Disc

By comparison, fusion requires an open incision in the patient's back that may range in length depending on how many discs are affected. Patients with disc replacement usually begin physical therapy at 6 weeks and can return to normal function in 3 months. Patients who undergo fusion begin physical therapy at 3 months and return to most activities at 6 months. Preliminary results from the trial indicate that disc replacement and fusion provide comparable medium-term results; long-term results with disc replacement remain to be assessed. At present, this surgery is restricted to diseased discs in the lumbar spine, the area that corresponds to the lower back.

Other examples of minimally invasive procedures of the spine include the use of intradiscal electrothermoplasty (IDET), another technique used in the treatment of degenerative disc disease. Using fluoroscopy (x-ray) as a guide, the surgeon inserts a needle into the disc space. He or she then puts a heated catheter through the needle and wraps it around the disc. "In heating the disc, you essentially 'spot weld' some of the annular tears, those that occur in the outer cartilage of the disc that cause pain. The heat may also denervate small pain fibers resulting in additional pain relief," says Dr. Cammisa.

Dr. Cammisa also performs a number of minimally invasive surgeries with the use of endoscopes (an instrument that provides a view the interior of the torso) and arthroscopes (an instrument that provides a view inside a joint). This technology allows orthopaedic surgeons to address various conditions of the spine, using only small incisions to position the scopes, a miniaturized camera, and small instruments. One of the most successful of these procedures is micro-discectomy to provide relief of pain caused by herniated discs that are compressing or pinching a nerve in the spine. A small incision of an inch or so is made, the disc fragment is removed from the spine, and pressure is taken off the nerve. Patients are generally hospitalized for about 24 hours and go back to work in about a week to ten days.

Illustration of spine vertebra.

Illustration of herniated disc

Other endoscopic surgeries include those done to treat:

• deformities
• trauma
• infection
• or to perform a biopsy

Computerized Image Guidance

Computerized image guidance enables orthopaedic surgeons to view parts of the spine that are not otherwise visible to the naked eye. For example, a traditional open incision in the patient's back reveals only the back (posterior view) of the spine.

With this new technology, a three-dimensional model of the surgical area-and three additional images of the spine-are created using CT scans obtained in advance. Using this information the surgeon can plan the procedure very precisely. During surgery, once the spine is exposed, the surgeon "matches" the surgical area to the previously obtained images, which act as a guide.

Locate a three dimensional point in image space and match it to the surgical space

Interactive, permits movement (surgical navigation)

For example, if the surgeon wants to drill a hole in a pedicle (a piece of bone that helps form the vertebral arch) as in a fusion surgery, computer-guided technology helps the surgeon ensure that the drill does not go through the vertebral body into an area that cannot be visualized.

"The idea behind computer-guided imaging is that we'll be getting better images at the same time we move away from larger incisions," says Dr. Cammisa. "This technique also helps reduce the risk of errors."

Biological Bone Growth Enhancers/Bone Growth Factors

Bone growth factors are materials that "encourage" the formation of new bone and thereby speed healing. These materials include de-marrowized bone matrices or DBMs (which come from donated bone) and bone morphogenic proteins or BMPs. BMPs are found in the patient's body; 17 different types have been identified. Researchers theorize their role is to promote different kinds of bone growth. Once the protein has been identified, it can be made in a laboratory through a recombinant process.

Skeletal repair without rhBMP-2

Skeletal repair with rhBMP-2

Presently, one type of BMP has been approved for use in patients who require fusion of vertebrae at a single level of the spine. The orthopaedic surgeon makes an incision in the front of the body, removes the disc, and then places a small titanium cage in the spine that contains BMP to enhance healing, i.e. the fusion process. "The idea behind this is to eliminate the need for a bone graft either from the patient or a donor," explains Dr. Cammisa.

<The orthopaedic surgeon inserts a small titanium cage in the spine containing BMP to enhance healing.

Clinical application of recombinant BMP

In patients who undergo laminectomy, a procedure in which the surgeon removes that portion of the vertebra that forms the "roof" of the house-like structure of the spine, (as seen in the drawing below), the vertebrae must sometimes be fused. In such cases the bone may be mixed with the BMP or the DBM to obtain a better fusion.

"House Analogy" Basement Disc

Clinicians in the spine service at HSS also work closely with individuals in the Department of Biomedical Mechanics in identifying and developing additional bone growth factors.

Other Advances

In addition to the advances described, the use of epidurals or local anesthesia with or without sedation has reduced the complications associated with spine surgery performed under general anesthesia. So-called "bloodless" surgery is also the norm at HSS, whenever possible. In order to limit or eliminate the need for transfusions of donated blood during surgery, patients who are scheduled to undergo major spine surgery can donate their own blood in advance. During surgery, the orthopaedic team may use a cell saver, in which the blood is recycled. Or, hemodilution may be used, in which the anesthesiologist draws off one or two units of blood, replaces it with normal saline, and reserves the blood for later use in the surgery-when a higher blood count is needed. All of these methods help protect patients from the minimal risk of infection that is associated with donated blood.

The Future Of Minimally Invasive Surgery

Among those developments Dr. Cammisa anticipates, is use of computerized image guidance for percutaneous procedures, those done with small punctures through the skin rather than incisions. In patients with early degenerative changes to the disc that affect only the nucleus (the interior gel-like portion of the disc), for example, nucleus replacements may soon be available. (These implants are currently being used in Europe with favorable results.) During surgery, images from the computer guide the surgeon into the disc space where a needle or catheter is inserted to remove some of the disc and to replace it with the hydrogel prosthesis.

As might be expected, many minimally invasive surgery techniques are explored first at academic centers. With the help of companies who are developing and marketing the technology involved, these techniques are becoming more widespread at hospitals throughout the country. However, if you are considering minimally invasive surgery of the spine, it's advisable to seek the care of a physician with considerable experience in the area.

"Orthopaedists who specialize in spine surgery are enthusiastic about minimally invasive technologies, as are patients," says Dr. Cammisa. "But it's important to realize that there are still going to be individuals for whom fusion will yield the best results and those who require open surgery."