This a very interesting question and there are several answers. Minimally invasive spine surgery has many meanings to many people, both patient and doctor. There are so many terms to describe the varying types of “minimally invasive” spine surgery. There is laser spine surgery, percutaneous discectomies, endoscopic spine surgery, endoscopic laser spine surgery, myeloscopy, and minimally invasive fusions etc. The list of procedures is exhaustive and the promotion and marketing is confusing.
The concept of “minimally invasive spine surgery” is obvious and appealing. Smaller incisions, less soft tissue damage, less pain, less need to spend time in the hospital, less rehab (if any), less pain pills (opioids), and less scar tissue formed.
Different Types of Minimally Invasive Surgery
One question, is all minimally invasive spine surgery the same? The answer is clearly, no. There is no clear consensus of what “minimally invasive spine surgery” is. I think the goals of all minimally invasive spine surgery are similar, but the ways of getting there are quite different. It also depends on what one is trying to accomplish during the surgery (discectomy, rhizotomy, decompression of stenosis, or fusion).
How minimal can one be? That is clearly the question. The intelligent answer is that “It depends”. It depends on the 1) size of the incision (exposure) and 2) the type of procedure (fusion vs discectomy) being done.
Let’s talk about the size of the incision. The size of the incision is determined by how much exposure is needed to “see” the problem that needs to be addressed. There are 3 ways to “see” the problem, and each needs a corresponding incision size. Visualization is everything to performing safe spine surgery.
The first way to see is to look directly at something. When looking directly at something, we need light. Somehow light needs to get to the problem. The light usually comes from the ceiling lights in the room or a light source worn on the forehead of the surgeon (like a miners light). This light source is external and outside the skin. The obvious problem here is that the smaller the incision, the smaller the opening and the less light that can come in. The amount of light available to see is further compromised by the instruments being used to perform the operation.
The instruments cast shadows when an external light source is used. Enter the operating microscope; it has its own light source and magnification. The light source is closer to the patient, but still remains outside of the patient and shadows are still cast by the instruments. The size of the incision can still remain sizeable, even when operating through a tube. The tube will have to be large enough to allow the light to get in and pass the instruments. This approach is more “minimally invasive” that previous open surgery was.
The second way to see during an operation is even more “minimally invasive”. The reason it is less invasive is that the light source is located inside of the body and does not have to shine in from outside of the body. The light source is located on the tip of a “scope” next to a camera lens with magnification. This describes an endoscope or arthroscope that has been around for decades. (https://www.youtube.com/watch?v=X3Kz50-iDhg) Its first use was in urology and later on in orthopedic knee and shoulder surgery. Now there is a scope for almost all types of surgery. These scopes are typically between 3.5 – 5.5 mm in diameter, which is pretty small.
The scope is typically passed through a hollow tube that allows passage to the surgery site. With the light source on the tip of the scope, there is no need for a large incision and the instruments don’t cast much of a shadow if any at all. The instruments, irrigation, suction, and laser can all be passed through hollow working channels in the tube or scope. This is direct vision at its best – a bright light and some variable magnification.
The only drawback with the endoscope is it requires looking at a TV screen on the wall instead of looking at one’s hands. It’s normal for a sports surgeon operating on knees and shoulders, but not so for the typical spine surgeon. Endoscopic spine surgery is only now (2014) being taught in residency and I only know of a couple of programs that have recently started training with these techniques. Endoscopic surgery is a special skill set that needs to be developed and practiced over time.
The third way to “see” during a minimally invasive spine surgery is without using light at all. Of course you say, how can this be?
The way this can happen is to use fluoroscopic x-ray to monitor the location of something metallic passing into the body.
This could be a needle or small tube that a laser fiber could be passed through. This is how these small metallic bands are placed in the spine (MILD procedure). Watching a fluoroscope is how a myeloscope is placed and followed during a procedure. Another example is a discogram, when fluoroscopic x-ray is used to direct and place a needle a disc to inject some dye. This is how a radio frequency probe is placed in the spine to perform a rhizotomy.
Obviously, this third way of seeing (with X-ray or CT) offers the most minimally invasive approach, but has one major shortcoming – there is no direct vision! In most situations where tissues are in close quarters and are being operated on, direct vision is essential for patient safety.
The Smaller the Incision, The Better
There is no question that there is going to be a larger approach and more soft tissue damage with a larger procedure like a disc replacement or fusion compared to an endoscopic procedure. In my mind, do as small of a procedure, through as small as an approach as possible for any given surgical problem. Remember, the smaller the approach, the more practice that is needed to do it successfully and safely.