Promising Advances in Minimally Invasive Spine Surgery

Richard G. Fessler

“Prescience” is not so much the ability to see the future as it is the ability to see where the future must go. It is in this sense of the word that I have pursued my career, and also in which I write this chapter. In which direction minimally invasive spine surgery (MISS) will progress is impossible to know, especially in the context of the current uncertainties of health care in America. As explained by the eminent athlete and philosopher, Yogi Berra: “It’s hard to make predictions, especially about the future.”

Although basic instrumentation has come a long way since our early attempts at MISS, available “tools” still have significant limitations. Take for example the most common MISS procedure performed, minimally invasive lumbar diskectomy. Many systems are available to perform this surgery, but all have limitations. If we first consider the area of visualization, limitations exist whether the technology is endoscopic or microscopic. On the one hand, endoscopic visualization gives one the advantage of excellent image quality of the working area and the tip of the instrument without the instrument’s handle and the surgeon’s hand obstructing the operative field, and without the “hassle” of bumping the instruments into the microscope lens when entering or exiting the wound. The price paid for this advantage, however, is the necessity of working in a two-dimensional visual field with a moderately bulky camera lens obstructing part of the working channel.

To circumvent the frustration many surgeons expressed in attempting to perform endoscopic minimally invasive diskectomies, tubular retractors and instruments were designed to enable surgeons to use the same technologies using microscopic visualization. This solved the problem of working in a two-dimensional visual field, but, as already indicated, created the problems of having the surgeon’s hands and shaft of the instrument in the relatively narrow visual field, thus obstructing a clear view of the surgical site. To partially address this problem, bayoneted instruments were developed. These did help remove the surgeon’s hands, but not the instrument’s shaft, from the visual field. Furthermore, in many instances, making an instrument bayoneted impairs the function of that instrument. For example, because the working mechanism of a straight curette is achieved through turning the cutting edge at the tip of the instrument, bayoneting the shaft fundamentally changes the motion necessary to turn the tip and significantly impairs the effectiveness of the instrument. As the complexity of the surgical procedure increases, the limitations imposed by the instrumentation is compounded.

Given the limitations to endoscopic technique, are there other reasons why one might wish to utilize endoscopic rather than microscopic surgical technique? Yes. Several surgeries have significant ergonomic advantages when one is utilizing MISS technique. For example, MISS cervical foraminotomy/diskectomy can be performed with the patient either sitting or prone. To reach the operative site when using the microscope with the patient in the sitting position, the surgeon’s arms must extend the entire length of the microscope for the duration of the surgery. A more comfortable position, of course is to do the microscopic foraminotomy with the patient in the prone position. However, the epidural venous plexuses surrounding the cervical nerve roots are abundant and can lead to profuse bleeding. In the patient in the prone position, this bleeding rapidly collects in the limited space of the tubular retractor and obscures the lens, making visualization difficult to impossible. However, using the endoscope with the patient in the sitting position both alleviates the discomfort of prolonged extension of the arms and the problem of excessive bleeding. Therefore, endoscopic cervical foraminotomy is one of the procedures where the endoscope has significant advantages over the microscope. Similar ergonomic advantages exist for micro endo scopic vs microscopic decompression of lumbar stenosis.