Indications for Spinal Fusion

x-ray of disc collapse
Fig 1: X-ray of disc space collapse at L4-L5
(larger view)

The biggest risk for spine fusion procedure is continued pain, meaning that the surgery did not substantially reduce or eliminate the patient's pain. The number one reason this occurs is that the fused disc was improperly identified as the cause of the patient's pain, so fusing the disc was unnecessary and irrelevant. This is why getting an accurate diagnosis is critical.

One of the most difficult and crucial parts of any type of low back surgery is selecting the patients who will do well with a certain procedure. It is especially critical to select the right patients for a lumbar spine fusion surgery for two reasons:

  • Lumbar spine fusion is an extensive surgery and the healing process takes a long time (about 3 to 6 months, and up to 18 months)
  • The spine fusion forever changes the biomechanics of the back and is thought to increase the stress placed on the other (non-fused) joints in the lower spine and possibly lead to degeneration of the adjacent levels of the spine.

Lumbar spine fusion surgery is generally not recommended until a patient has tried 6 to 12 months of adequate non-surgical care. For more details on non-surgical treatment options, please see Degenerative Disc Disease Treatment for Low Back Pain.

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Proper Patient Selection for Lumbar Spine Fusion Surgery

Spinal fusion is best for treating low back pain caused by severe degenerative disc changes and is best for treating one, or maybe two, levels of the lower spine (typically the L4-L5 level and/or L5-S1 level).

Prior to recommending or offering spine surgery, a surgeon must also consider other causes of low back pain that can closely mimic the symptoms of degenerative disc disease. These conditions include:

If a patient's low back pain and other symptoms do not improve with extensive conservative (nonsurgical) treatment and other causes of low back pain have been ruled out, then he or she may be considered for a spine fusion surgery. Importantly, while failing conservative treatment is a necessary prerequisite for spine fusion surgery, it is not sufficient. Prior to recommending spine fusion surgery, a spine surgeon has to be confident that he or she is fusing the segment of the spine that is generating the patient's pain (the "pain generator"). Obviously, fusing a structure that does not cause pain will not reduce the patient's low back pain or lead to a successful outcome.

MRI scans have greatly increased the spine surgeon's ability to diagnose degenerative disc disease. Unfortunately, a lot of the changes that are seen on MRI scans are more related to normal aging than to a pathologic and painful disc. Differentiating a painful disc from an aging disc is often difficult but there are some clues that help. In general, a painful disc will be severely degenerated whereas the rest of the discs will be well preserved. Other characteristics of a painful disc on an MRI scan of the spine include:

  • Disc space collapse (see figure 1), which means that the disc has gotten shorter/flatter
  • Endplate erosion, which is erosion of the top and bottom outer material of the disc
  • Edematous changes in the vertebral body (Modic changes), which is when the MRI shows irritation of the bone marrow, may be an indicator of a painful disc. There is a characteristic bright signal on the MRI scan when this occurs.

If a spine surgeon is uncertain as to whether or not a disc is painful, a CT-discogram may be ordered. A discogram is a direct pain provocation test that is designed to try to elicit the patient's pain by injecting a dye into the disc space. If the test creates the patient's normal pain, it can be assumed that the test is positive and the disc is generating th/files/thumb/Lumbar-Microdiscectomy-Surgery-Video-Thumb.jpg

  • It involves an injection into the spine, which has several risks (albeit rare)
  • It is usually painful
  • It is a subjective test, and both false positives and false negatives can occur
  • Accuracy of the test is largely dependent on the skill of the discographer
  • Discograms are used by some surgeons before every spine fusion, and it is certainly warranted to gather as much information as possible before undergoing a fusion procedure. However, discograms are probably not necessary on a routine basis, and the test itself is somewhat controversial. The test should only be used if the results are going to change the surgeon’s recommendations (e.g. if negative, spine surgery will not be recommended). If the results are ignored and the surgical choice is made off of the MRI findings, then a discogram does not serve any useful purpose.