Posterior lumbar fusion has traditionally been performed through a midline or paraspinous approach. In a midline approach the muscles over the spine are elevated from the bone allowing decompression, of nerves placement of graft and instrumentation. A paraspinous exposure requires two parallel incisions on either side for the same purposes.

Decompression of the spinal canal can be performed at one or more levels including removal of herniated discs and other pressure on the spinal nerves.

Following decompression, instrumentation can be attached to the vertebrae to provide stability, correct deformity, and maintain a particular alignment until a fusion develops. These implants usually consist of hooks or screws attached to bone and connected by rods or plates. The surface of the spine is removed (decorticated) and bone graft laid on this surface. Bone graft is commonly obtained from the pelvis through the same or sometimes a separate incision. The decorticated surfaces then grow to the graft and form a solid bar of bone much like a fracture heals. Ultimately, this provides the stability needed and prevents further progression of deformity, etc… Banked bone (allograft) or bone substitutes have generally been shown to be inferior to the patients own bone (autograft) in developing a solid fusion posteriorly. Early reports using Bone Morphogenic Protein are encouraging and may increase fusion success rates, in the future, which at present may at best be between 85 to 95% when instrumentation is used.