Possible risks and complications with placement of lumbar instrumentation include:

• Non-union
• Adjacent Disc Disease: Recurrent pain after successful spinal fusion and instrumentation procedure is more likely due to a "transfer" lesion at the motion segment above or below the fusion, because stress is transferred to the next level and may cause that vertebral segment to degenerate and breakdown.
• Nerve Damage: Nerve damage can occur with placement of the instrumentation, or if the instrumentation dislodges or migrates.
• Bleeding
• Infection

Risks with the procedure are very particular to the surgical approach that is used (PLIF or ALIF). There is an additional risk that the anterior cages may extrude out of the disc space.

Posterior (pedicle)
An analysis of 2,500 patients by 350 physicians conducted by the North American Spine Society found that the complication rate with using pedicle screws in spinal fusion surgery is low. There is about a one in 1,000 chance of nerve root damage, and a 2% to 3% chance of infection. While there was a rod and screw breakage rate of approximately 10% in the 1980's, with modern pedicle screws the breakage rate has now been reduced to about one in 1,000.

Posterior (Interbody PLIF or TLIF)
If the cages are placed through a PLIF or TLIF, the cages can potentially extrude into the spinal canal and can produce significant neural injury. During retraction of the nerves and placement of the cages, neurologic injury can result. The PLIF procedure requires substantial retraction of the nerve roots to gain access to the disc space. Significant traction can injure the nerve root and has the potential to result in chronic leg pain and back pain. The pain associated with this type of nerve root injury can be severe, and there are no effective options for treatment. The TLIF requires less retraction of the dural sac, but nerve injury can occur at the level of the nerve cell bodies (dorsal root ganglion). Pain associated with manipulation of the DRG can also be very severe and debilitating. Fortunately, these complications are rare with meticulous care of the nerves.

Anterior (ALIF)
Anterior instrumentation has the risk of an injury to the largest blood vessels (aorta, vena cava), or injury to the nerves that pass adjacent to the disc. The cages can also potentially extrude into the abdominal cavity and may need to be retrieved to prevent them from eroding into a major blood vessel.

If the cages are placed to the side of the disc rather than in the middle, the cages may impinge on a nerve root. Also, during placemen of the cages, disc material can be inadvertently pushed back into the spinal canal leading the nerve impingement. There is also a theoretical risk that the cages could break, although this is unlikely. Infection is also a remote possibility.

In males, there is a small risk of retrograde ejaculation with anterior approaches at L5-S1. The nerves that control ejaculation lie over the front of the L5-S1 disc. They are very sensitive, and therefore even with retraction the normal coordination of ejaculation can be disrupted resulting in the ejaculation occurring backward into the bladder. It should be noted that erection and sex drive are not significantly affected. The risk of this complication has been noted to be 0-5% in different studies. Other risks include injury to the ureter or injury to the bowel.