Minimally invasive spine fusion systems

Introduction to minimally invasive spine surgery
Much of the published minimally invasive spine surgery techniques today describe less invasive methods of performing a spinal fusion with pedicle screw instrumentation. This article will review the major developments in minimally invasive surgery systems for posterolateral fusion and pedicle screw fixation.

While this article reviews minimally invasive spine fusion surgery systems, it is important to note that many surgeons are able to perform traditional fusion ("open fusion") using surgical techniques that are considered "minimally invasive", such as relatively small surgical incisions, minimal muscle or other soft tissue damage, etc. Generally the minimally invasive spine surgery techniques discussed below decrease the muscle retraction necessary to perform the same operation, in comparison to the traditional open spinal fusion surgery.

Said another way, using a minimally invasive spine surgery system does not guarantee that the spine surgery will be less invasive than using a more traditional open surgery technique. This is because there are several factors (other than type of system used) that have a major impact on the outcome of any spine fusion surgery, including the surgeon's skill and experience, correct diagnosis and indications for a spine fusion, and the type of fusion and surgical technique that is used.

Minimally invasive spine surgery systems
In theory, any minimally invasive spine surgery system for a fusion should be able to perform the same spine fusion as the traditional open technique, but through several smaller incisions instead of one longer incision. Additionally, some physicians feel that using a minimally invasive spine surgery system allows them to cause less soft tissue damage; however, this has not been proven in the medical literature and some spine surgeons disagree with this assertion. It is important to note that the use of minimally invasive spine surgery systems requires special training, experience and expertise, which some spine surgeons may not be interested in or trained in.

Advanced technology is partly responsible for the advent of minimally invasive spine fusion surgery techniques.

• The use of advanced fluoroscopy (x-ray imaging during surgery) has improved the accuracy of incisions and hardware placement, minimizing tissue trauma while using a minimally invasive system.

• Improved optics, cameras and lighting systems enable surgeons to visualize key anatomic structures through small incisions.

Three types of minimally invasive spine fusion surgery systems will be discussed in this article. Pedicle screw fixation with deep placement of rods is traditionally one area that has presented significant challenges for minimally invasive approaches, and these three systems tackle those challenges in different ways, with distinct advantages and disadvantages. All the systems use similar methods of monitoring and guiding the placement of pedicle screws.

Pedicle targeting is the technique of identifying the appropriate location and pathway for the screw to take in order to stay within the pedicle itself and not penetrate through the pedicle into surrounding tissue. Vital structures such as the nerve roots and dural sac are present within millimeters of the pedicle at certain points. Other important vessels and structures are in close proximity to the lumbar pedicles. Staying within the confines of the pedicle is therefore of paramount importance when placing pedicle screws.

Upon identifying the pedicle starting hole, the wire or probe is carefully advanced through the pedicle using frequent fluoroscopic confirmation as shown in figure 2. A three-dimensional understanding of the anatomy is very important and must be brought into play by the spine surgeon to pinpoint the exact location of the screw in the pedicle.