The Pros and Cons of Spinal Fusion Surgery
Answer: While there are some drawbacks to having a fusion, let's first address the advantages. A decompression surgery relieves nerve pain by making more space around the spinal cord and nerve roots. However, decompression can often lead to instability at the affected level. ("Level" is the word doctors sometimes use to refer to individual vertebra.) Sometimes when enough bone is removed to decompress the nerves, the discs and facet joints can no longer maintain proper stability. When this happens, the spine moves in abnormal ways.
By fusing the level, there is less concern that the patient will need surgery again at that level. If the discs and/or facets are pain generators, as is often the case, a fusion will ensure that motion at the level is stopped, potentially eliminating the low back pain.
A second advantage of fusion is that it reduces post-decompressive deformity. Some patients develop post-laminectomy kyphosis, which is an abnormal alignment of the spine. This too can often lead to additional surgery. Similarly, a fusion can correct any deformity the patient had before surgery and ensure that the normal alignment of the spine is restored. This may reduce wear and tear (and need for future surgery) on the neighboring levels.
On the other hand, there are some potential disadvantages. A fusion involves extensive bone work, which can lead to more back pain and longer recovery. The lateral facet joints and transverse processes (specific parts of your vertebra, both located on the sides of each vertebra) are typically exposed during a fusion. This necessitates more muscle dissection.
Bone graft or bone substitutes are also placed in the spine to help your bones gradually fuse together, but inflammation can result and potentially lead to more scarring (arachnoiditis) and subsequent pain.
Most fusions involve placing rods and screws that aim to stabilize the spine until the bony fusion grows solid. There is a slight risk of this hardware causing nerve irritation and perhaps new or residual leg pain/weakness.
Finally, a fused segment ("segment" refers to two vertebrae and the disc in between them) may cause more stress on the level above and below the fusion. This is called adjacent segment disease and is a source of debate among spine surgeons. It seems reasonable that a rigid segment next to a mobile segment will cause additional stresses at the mobile segment, potentially causing degeneration. However, many theorize that the neighboring levels may wear out regardless, since degenerative spine disease is a chronic condition that typically encompasses many levels.
Your question about mobility is a common one. It is rare for a patient to notice much limitation with a one- or two-level fusion. Often patients who had back pain along with their stenosis have increased mobility when those painful segments are immobilized. Patients with fusion at many levels or even a complete thoraco-lumbo-sacral fusion (as often is performed for severe scoliosis) can still lead relatively normal lives.
Most bending over the trunk occurs at the hips, and even a multi-level fusion still affords a lot of mobility. But rotation is typically more restricted. However, many patients with one- or two-level fusions can still play sports (like golf, for example) once they are healed.