Evaluating spinal fusion surgery

Spinal fusion is indicated for the treatment of a large variety of spine problems. A common reason to perform spinal fusion is disc-related back pain, often referred to as degenerative disc disease. It can also be performed to treat painful arthritis of the facet joints (the small paired joints which sit behind each disc and contribute to motion), as well as back pain associated with instability of the spine (such as spondylolisthesis) and progressive deformity of the spine (such as scoliosis or ankylosing spondylitis).

How are spinal fusion operations done?

Spinal fusion represents many different specific surgical techniques and options, each with their unique potential risks and benefits. These include:

• Operating on the front of the spine (anterior), the back (posterior), or both (anterior/posterior, circumferential, or ‘360’), are all potential surgical options.

• Use of the patient’s own bone for bone grafting (“autograft”), a bank (cadaver) bone, or bone forming molecules (bone morphogenetic proteins, or BMPs) are also options to help create the bone fusion, as is the potential use of metal rods and screws (internal fixation) to aid in the healing of the fusion and minimize or eliminate the need for postoperative external bracing.

A complete discussion of the types of techniques for spinal fusion and the reasons to perform one technique over another is beyond the scope of this article. Patients should be sure to become educated about and have a thorough discussion regarding surgical options with their doctor if spinal fusion is recommended as an option to treat low back pain.

Does spinal fusion limit the patient’s mobility?

As one of the goals of spinal fusion is to stop painful motion of the disc or facet joints, this procedure stiffens the spine as a matter of necessity. However, if the motion of the low back is severely limited due to pain preoperatively, overall clinical motion following fusion can be similar or even better than before surgery if the pain is successfully relieved. Even if the motion seems the same or greater after surgery, the motion at the fused disc(s) is (are) always severely limited, and the motion seen clinically is made up of increased motion from surrounding discs and/or the hip joint. This is less of an issue for the L5-S1 segment if it is fused, as this segment has less motion to begin with.

Does healing of the fusion guarantee relief of pain?

Successful bone healing of the fusion is generally needed for long term pain relief, but unfortunately successful bone healing does not guarantee pain relief.

Fusion rates of 60 to 95+ % have been reported depending on the fusion technique used (higher fusion rates are generally seen using the more invasive techniques with added surgical risk), but clinical success in term of satisfactory improvement in preoperative pain occurs in only 50-80 % of patients. This is thought that to be due at least in part because of diagnostic challenges, so that even if there is a successful fusion, if the patient’s pain was not caused by motion at that disc space, the patient will still have pain after surgery. When a patient continues to have pain despite fusion surgery, this is generally referred to as failed back surgery syndrome.

What are the common complications associated with spinal fusion?

The potential complications specific to a spinal fusion procedure depend in part on the surgical technique used. These can include:

• Postoperative wound infection is the most common complication, occurring in about 1-5% of cases. The risk of a postoperative infection is higher when metallic fixation is used, and is also higher in diabetic and overweight patients.

• Pain from the bone graft site in the pelvis, if used, is very common for the first 6 to 8 weeks following surgery. Some amount of this pain may persist and become chronic in 15 to 30% of cases.

• Failure of bone healing of the fusion (“pseudo-arthrosis”) can occur in 5 to 40% of cases, depending on the specific surgical technique used and the patient’s individual risk factors. If metallic implants were used and the fusion does not heal, this will eventually result in loosening or breakage of the screws or rods, as they are not meant to be relied upon to stabilize the spine indefinitely.

Persistent pain due to failure of the bone to fuse will often necessitate additional surgery to get the fusion to heal. Revision fusion surgery is commonly larger than the initial procedure, and may have added risk. The patient’s individual risk factors also play a role in fusion rates (for example, patients who smoke have lower fusion rates. Again, discussing and understanding all of the surgical risks and complications of any recommended fusion procedure is critical.

Are there long-term negative consequences of spinal fusion?

As a result of stiffening of the spinal segment(s) with spinal fusion, added stress with spine motion is placed on the remaining mobile discs above and below the fusion. This may accelerate the process of disc degeneration of adjacent discs, and additional surgery may be needed to the surrounding discs due to pain from degeneration, instability, or nerve compression in the future. This process is sometimes called “adjacent segment disease” or “transitional syndrome”, and it remains somewhat controversial just how much increased the rate of adjacent disc degeneration is attributable to the fusion and aftereffects, versus what amount of degeneration of the other discs would have occurred naturally without a spinal fusion.