In the surgical treatment of lumbar spondylolisthesis, there are two basic goals. The first goal is to eliminate the compression of the nerve roots by excision of compressive bone, ligaments, and disc material surrounding the nerve roots. The second goal is to stabilize the two vertebrae by placement of bone grafts, screws, and rods to stabilize the vertebrae and fuse them together.
Traditionally, the process of decompression and fusion has been accomplished through a wide surgical exposure of the posterior aspect of the affected vertebrae. A laminectomy is performed to relieve pressure on the nerve roots. Bone graft is removed from the posterior hip bone (iliac crest) through a separate incision. The bone graft is layered on both sides of the exposed spine. Pedicle screws are placed into the vertebrae and connected by rods to immediately stabilize the unstable vertebrae. The bone grafts provide long-term stability once they have fused to the vertebrae (usually 3-6 months). This procedure can require a four- to six-inch incision over the spine, with stripping of the spinal muscles away from the spine, over three to four vertebrae, to gain adequate exposure. The incision on the hip for harvesting of the bone graft is usually three to four inches long. Both of these incisions remain painful for many weeks after surgery, prompting the quest for better methods.
The evolution of minimal access surgical techniques (MAST), new instrumentation (METRx, Sextant) , new techniques to achieve fusion (BMP), and surgical image guidance technology (Stealth, ISO-C3D C-arm ) have made it possible to achieve the goals of decompression, stabilization and fusion, through multiple small incisions, minimizing surgical exposure of the spine, decreasing blood loss, reducing post-operative pain, and shortening recovery time. The procedure can be done without harvesting bone graft from a separate incision. The fusion process takes place between the vertebrae within the disc space (interbody fusion), rather than around the sides of the vertebrae. An interbody fusion is believed to be a more stable fusion with a higher rate of success. The procedure performed to fuse the vertebrae through the level of the disc space is called a posterior lumbar interbody fusion or a transforaminal interbody fusion.
ISO C-3D images are combined with the Stealth surgical navigation system to guide instruments through small incisions to defined points on the spine. The guidance system is, in turn, combined with the Sextant pedicle screw and rod insertion system to precisely place pedicle screws through half-inch incisions for the treatment of spinal instability.
The discectomy and interbody fusion is performed through a one-inch incision using the METRx tubular retractor system.
The following photographs illustrate a minimal-access technique used to perform a TLIF on a patient with spondylolisthesis.