Posterior (pedicle)
Pedicle screws provide a means of gripping onto a vertebral segment from posteriorly and limiting its motion. The screws are placed at two or three consecutive spine segments and then a short rod is used to connect the screws. The screws are generally made with titanium. After the bone graft grows, the screws and rods are no longer needed for stability and may be safely removed with a subsequent back surgery. However, most surgeons do not recommend removal unless the pedicle screws cause discomfort for the patient (5% to 10% of cases).

Anterior (ALIF)
Anteriorly, cages can be placed in the disc space or to replace the vertebral bodies. Many different cage shapes are available including cylindrical and rectangular. These can be made of titanium, carbon fiber, or composite material. Additionally, these same shapes can be made with allograft (donor) bone. Most of the cages are placed in the front of the spine (anterior lumbar interbody fusion or ALIF). The cages can be inserted through a small incision (minilaparotomy) or with an endoscope (a scope that allows the surgery to be done through several one-inch incisions.

Approaching the disc from the front allows almost all of the disc and its inflammatory proteins to be excised. Placing the cage in front also allows the disc space to be distracted (jacked open), and restoring its normal height gives the nerve more room and relieves pinching on the nerve. There is minimal muscle dissection, allowing all the back muscles (erector spinae) to be available for rehabilitation.

The cages work particularly well in one or two-level degenerative disc disease, isthmic spondylolisthesis, or post laminectomy syndrome, especially in younger patients (30-60 year olds). For certain conditions, the ALIF with cages is also useful to decompress the exiting nerve root by distracting the disc space to alleviate pain associated with pressure on the nerve.

ALIF and instrumentation can be performed "stand-alone", or in combination with posterior instrumentation. Anterior interbody cages are titanium or allograft bone cylinders that are placed in the disc space. The cages are porous and allow the bone graft to grow from the vertebral body through the cage and into the next vertebral body. The cages offer excellent fixation, so most patients do not need additional instrumentation (e.g. pedicle screws) or post-operative back braces for support. "Stand-alone" cages, however, are not recommended for elderly patients (over 60 years old), especially for patients with significant osteoporosis (bone thinning). To be effective, the cages need good vertebral body strength to allow for solid purchase in the bone. It is also not advisable to use in patients who still have a large disc space. Fixation is much better in those with a collapsed disc space.

Posterior (Interbody - PLIF or TLIF)
While most cages are placed anteriorly, they can also be placed in the back of the spine (posterior lumbar interbody fusion or PLIF) through a midline incision in the back. A transforaminal lumbar interbody fusion or TLIF is an alternative approach performed by removing the facet and accessing the disc through the foramen. A laminectomy and facetectomy, and some retraction of the nerves are necessary to allow access to the disc. The cages can be made of titanium, carbon fiber, or composite material. Additionally, these same shapes can be made with allograft (donor) bone.