Minimally Invasive Procedures

Percutaneous lumbar fusion

Percutaneous fusion is a minimally invasive form of fusion for the lumbar spine, performed through several small skin incisions. Typically, patients who are fusion candidates have degenerative disc disease and long standing back pain. The back pain is usually worsened by motion. Therefore the back pain is usually mechanical. Chronic axial pain is present (that is, pain across the back), and the patient may or may not experience radicular, or nerve root, pain. The reason why mechanical back pain develops is felt to be due to a long standing degenerative process. Initially, there is degeneration of the lumbar disc. This can lead to disc herniation. Over time, the disc degeneration, which can in and of itself generate pain, leads to micro-instability of the affected lumbar segment. Soon, the associated facet joints develop arthritis in this degenerative cascade. This is referred to as facet arthritis. The stabilizing ligaments of the spine may also become arthritic, leading to an expanding-bulging condition called ligamentous hypertrophy. Motion instability continues in this degenerative process and the arthritic and degenerative changes to the disc, facet joints and ligaments can continue.

Fusion works by limiting motion at the affected level. Therefore, for fusion to be successful, the correct spinal level must be fused. While this seems intuitive, many patients have advanced degenerative disease at multiple levels and not every level is necessarily painful. The correct level can be localized on MRI, if the degenerative process is limited to 1 or 2 levels. If there is multi-level disease, a discogram can be performed to help the surgeon identify the correct level. In discography, a needle is placed into the disc from the skin and dye is injected into the disc. Of course, a patient will not be considered for fusion unless he/she has failed extensive conservative therapy or a non-fusion procedure has first been considered.

In the fusion procedure, the surgeon removes the lumbar disc. In its place morsels of bone or bone paste is applied. However, fusion does not actually occur at the time of the procedure. It takes 3 to 6 months for the bony material to grow across the disc space and connect the two vertebrae together, obtaining the fusion. For this to occur, motion across the operated disc level must be limited. This is done by placing screws or screws and rods either across the operated segment or through the facet joints. This is called instrumentation and can also be done percutaneously, or through the skin.

The Axia-LIF, or axial lumbar interbody fusion, procedure is one type of percutaneous fusion. The procedure involves a percutaneous L5/S1 discectomy, fusion and implantation of an axial rod across the disc space to provide stability. In the Axia-LIF procedure a tube, called a cannula, is inserted through a small skin incision and advanced to the sacrum. The skin incision is adjacent to the buttocks. By placing the cannula through the sacrum, a trajectory up and down across the disc space can be achieved. This facilitates a discectomy and allows bony material to be placed into the disc space. A metal rod is then inserted through the cannula and across the disc space, anchoring the adjacent vertebrae together. Through a second small incision, screws are placed into the facet joints to stabilize the operated level until fusion takes place.

The Perc-LIF, or percutaneous lumbar interbody fusion is a second type of percutaneous discectomy. The Perc-LIF procedure starts off similarly to the minimally invasive percutaneous discectomy. Through a small skin incision in the back a discectomy is carried out. Following the discectomy, a collapsed mesh back is inserted through the cannula and into the disc space. The back is then injected, through the cannula, with bony material. The bag remains in the disc space to contain the material. Prior to the discectomy and bony grafting screws are placed in the vertebra across the diseases disc space. The screws are placed via a very small incision in the back, meaning that they are percutaneous. The screws, along with similarly placed rods, allow a distraction, or widening of the diseased disc space. This widening opens the normal structures through which spinal nerves pass. The widened disc space also allows the discectomy. The screws later serve to provide stability while bony fusion takes place.