Review of current minimally invasive spine fusion systems

The following is a review of three types of minimally invasive systems currently used in the US for performing a spine fusion surgery with pedicle screw fixation.

1. System 1—"Pathfinder"

The first minimally invasive spine surgery system necessitates an approximately 3 cm incision directly over the insertion site of the pedicle screws. The procedure involves no muscle retraction and minimal stripping of muscles.

The pedicles are addressed by placing a guide wire followed by a series of specialized instruments. Then the pedicle screw is placed over the guide wire (see figure 1). The screws are attached to C-shaped towers, which extend above the skin (see figure 2).

It is through these towers that the rod is passed into the screw head deep in the tissue and tightened in place with set screws. The towers are then removed (see figure 3 and figure 4).

This fusion surgery approach allows a posterolateral fusion to be performed with traditional instruments, and an interbody fusion is possible through tubes that use the same small incision. Multi-level fusions of more than two vertebra are possible with this technique.

This minimally invasive spine fusion surgery system allows for decortication and fusion to be performed thru the same incision with minimal retraction of the muscles, using traditional instruments and a head light. An interbody fusion is possible through tubes, which are commercially available to be utilized through the same small incision. Multilevel fusions with a screw at each level are possible as well.

2. System 2—"ATAVI"

The next minimally invasive spine fusion surgery system is similar in its incision and muscle sparing approach. It employs a special expandable retractor (see figure 5) in the area of facet joints and transverse processes. An endoscope allows visualization of the involved tissue and operative site (see figure 6).

Posterolateral fusion or PLIF may be performed through this portal. Pedicle screws are placed through the portal with fluoroscopic guidance and endoscopic visualization. The rod is then inserted and attached to the screws with set screws (see figure 7 and figure 8).

Placing the expandable retractor and adjusting the retractor during the surgery allows endoscopic visualization but at the expense of requiring additional surgical time, especially while gaining familiarity with the procedure.

This minimally invasive surgery system allows for decortication, fusion as well as interbody fusion through the same expandable lighted port which is used for placement of the pedicle screws. Multilevel fusions are possible as well.

3. System 3—"Sextant System"

The third minimally invasive spine surgery system is essentially a fixation system and does not allow for a posterolateral fusion. However, interbody fusions are possible with the addition of an access port (which requires a larger incision).

The spine fusion system provides pedicle screw fixation without fusion using three 1.5 cm incisions, with minimal soft tissue dissection. Each screw is placed through its own incision and a third incision is needed for placement of the rod into the screws. Screws are placed in a manner similar to the first system discussed (see figure 9 and figure 10).

The passage of the rod does create some muscle damage, and there are some nuisances associated with its passage (see figure 11). Once the rod is seated, placing and tightening the set screws is relatively straightforward (see figure 12).

This minimally invasive spine surgery system is essentially a fixation system and does not allow for a posterolateral fusion or interbody fusion through the regular incisions that are made for the placement of the pedicle screws. If the surgeon wishes to perform any of the latter procedures it would have to be done by enlarging the incisions and use of tubes as mentioned above. Multilevel fixation is possible with this system.