Spinal Fusion Surgery
Lumbar spinal fusion is a type of back surgery in which a bone graft is inserted in the spine so that the bones in a painful segment of the spine fuse together. The fusion aims to stop the motion at a vertebral segment, which should decrease the pain caused by the joint. After the surgery it will take several months (usually 3 to 6, but sometimes up to 18 months) before the fusion is set-up. This surgery has been improved over the last 10 to 15 years, allowing for better success rates, and shorter hospital stays and recovery time.
Indications and contraindications for spinal fusion
The vast majority of people with low back pain will not need fusion surgery and will be able to manage the pain primarily with physical therapy and conditioning.
A fusion surgery may, however, be recommended for patients with:
- Low back pain caused by degenerative disc disease that limits the patient’s ability to function (after non-surgical treatments, such as physical therapy and medication, have failed)
- Isthmic, degenerative or postlaminectomy spondylolisthesis
- A weak or unstable spine (caused by infections or tumors), fractures, or deformity (such as scoliosis)
Fusion is a major surgery. Consequently, it is very important that other possible causes of a patient’s back pain (e.g. facet or hip osteoarthritis, or piriformis syndrome) be ruled out prior to undergoing fusion surgery. Generally fusion should not be considered until the lower pack pain has persisted for more than six months, and a concerted effort at non-surgical treatment has not relieved the pain. The decision to have fusion surgery is almost always the patient’s choice as this is an elective surgery designed to help alleviate some of the patient’s pain and enhance his or her activity tolerance. It is exceedingly rare to have neurological consequences as a result of delaying or avoiding a fusion surgery.
Success rates for fusion
Fusion surgery success rates vary between 70% and 95%, and there are several factors that will impact the success rate of the surgery, including:
- Spine fusion for conditions that arise from gross instability (e.g. isthmic or degenerative spondylolisthesis) tends to be more successful than surgery done for pain alone (e.g. degenerative disc disease).
- Individuals with only one badly degenerated disc (especially L5-S1) but an otherwise a normal spine tend to fare better than those undergoing multilevel fusions. Fusion surgery is generally considered for one or possibly two levels, and multilevel fusions should be avoided except in cases of severe deformity.
- Individuals who have significant disc degeneration usually find more pain relief from a fusion than those with only minor degeneration on the MRI scan (e.g. still have a tall disc).
The most important success factor in fusion surgery is confirming that a patient’s back pain is truly caused by degenerative disc disease, rather than some other condition. This is done by a combination of a careful review of the patient’s history, a physical exam, and diagnostic tests (such as x-ray and MRI), and/or possibly a discogram.
Other health factors or activities can undercut the chances of obtaining a successful fusion, and should be treated or controlled prior to surgery if possible. These include smoking, obesity, malnutrition, osteoporosis, chronic steroid use, diabetes mellitus or other chronic illnesses.
A surgeon will consider different techniques and both anterior (from the front) and posterior (from the back) approaches to perform the fusion.
Posterolateral gutter fusion-the most common fusion technique, involves:
- Making a 3- to 6-inch midline incision in the low back
- Obtaining bone graft from the pelvis (the iliac crest)
- Elevating the large back muscles that attach to the transverse processes (small extensions of the vertebra) to create a bed for the bone graft to lay on
- Laying the harvested bone graft in the posterolateral portion of the spine, where it has the steady blood supply needed for the fusion to grow
- Moving the muscles over the bone graft to create tension to hold the bone graft in place.
Other commonly used fusion techniques include:
- Posterior lumbar interbody fusion (PLIF)-approached through the back, the surgery involves removing a portion of the facet joints, then removing the disc between two vertebrae and inserting bone into the space between the two vertebral (where the disc was)
- Anterior lumbar interbody fusion (ALIF)-similar to a PLIF, but approached through the front
- Anterior/posterior spinal fusion-this is done from the front and the back and combines the ALIF and posterolateral gutter fusion procedures
- Transforaminal interbody fusion (TLIF)-is essentially and extended PLIF in that in removes one entire facet joint (rather than a portion of the facet joints on each side of the spine) to gain access to the disc space
The type of fusion will depend largely on the patient’s diagnosis and surgeon’s preference. Regardless of which technique is used, the goal is to create a solid fusion in the affected motion segment, defined as the disc space in front of the spine and the paired facet joints in the back. Two vertebral segments need to be fused to stop the motion at one segment; thus an L4-L5 (lumbar segment 4 and lumbar segment 5) fusion is actually a one-level spinal fusion.
In addition, there are several types of bone graft options, including bone graft taken from the patient’s hip (autograft bone) during the fusion surgery, or from cadaver bone (allograft bone). The possibility of using synthetic bone graft substitutes (such as bone morphogenic proteins), which help the body create bone, may also be an option.
Potential risks and complications
The main potential risks of lumbar fusion include:
- Continued pain after surgery
- Solid fusion will not be obtained (nonunion) and further surgery to re-fuse the spine may be necessary
- Bone graft harvest site chronic pain
- Nerve damage (less than 1 in 10,000 chance)
- Infection or bleeding (rare)
- Anesthetic complications (rare)
- Cerebrospinal fluid leak (rare)
- Failure of the instrumentation (rare)
After a spine fusion surgery, it can take three to six months for the fusion to successfully set up and achieve its initial maturity. During these first months, patients should follow the surgeon’s postoperative care instructions and avoid activities such as high-impact exercise that may place the bone graft at risk. Permanent restrictions are only needed in a few cases, and since bone is a live tissue, after it has set up the bone graft will get stronger with some level of stress (activity). In general, a back brace after surgery should not be needed unless adequate fixation at the time of surgery was not acheived.
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