Spinal fusion surgery can effectively stabilize the spine following abnormal kyphosis, lordosis, or the removal of structural elements for decompression purposes (such as in a laminectomy and discectomy). Unfortunately, not all spinal fusion will achieve a solid union between the existing skeleton and the bone graft or implant. In a number of cases the non-union does not cause symptoms as it can improve spinal stability and relieve pressure to a degree significant enough to relieve a patient’s leg or back pain. In other cases the pseudoarthrosis (failure to fuse) can cause continued nerve compression, instability in the spine, and even extra pressure on the adjacent segments.
How Long Does a Bone Fusion Take?
In general there is an association between the formation of a solid union following spinal fusion with a better patient prognosis. However, it can be difficult for a surgeon to ascertain whether a solid fusion has actually occurred, particular when the use of hardware limits the visual access of MRI scans or X-Rays. Fusion can take anywhere from around three months to a year after surgery and further surgery is unlikely to be scheduled within a year of the first fusion procedure. Exceptions to this include cases where a clear hardware failure is evident, or where a significant degree of spinal instability can be seen which is extremely unlikely to be addressed through the usual bodily healing processes.
Contributors to Failed Spinal Fusion
Adjacent segment disease, also known as transitional syndrome, can also contribute to failed back surgery syndrome. This condition develops as a result of the new distribution of weight and pressure on the spine following spinal fusion. The solid, inflexible, long bone that results from successful spinal fusion can transfer pressure to the vertebral levels on either side of the new bone structure causing increased progression of degenerative disc disease, and the possibility of fractures of the joints above and below. Further fusion may be needed, but patients may experience difficulties as fusion over multiple levels is more likely to cause complications. A TLIF back surgery may reduce the degree of adjacent segment syndrome as it can effectively maintain intervertebral height and reduce the transfer of pressure to other vertebrae. Similarly, the use of artificial disc replacements may allow the spine to remain both stable and flexible following a discectomy, and reduce the need for fusion. Research continues in this area on appropriate materials and techniques to improve surgical outcomes.
Reoccurring Back Pain after Spinal Fusion
Recurrent pain that occurs many years after spinal fusion can be due to adjacent segment syndrome and is more likely in those undergoing a two-level fusion at say L4-L5 and L5-S1 for sciatic nerve pain. Younger patients, such as those thirty to fifty years old, are more likely to suffer a second incidence of back pain, usually attributable to their higher levels of activity and the relatively longer time span in which such problems can occur (compared to more elderly patients). Lower segment fusion, at L5-S1, does not usually cause subsequent pain as this portion of the spine is relatively stable anyway. Fusion at L4-L5 transfers considerable stress to the above L3-L4 segment as these are the more mobile vertebral levels.
Patients with other conditions, such as osteoarthritis, including degenerative spondylolisthesis and spondylosis, are more frequent sufferers of transitional syndrome. If patients have undergone spinal fusion following a discectomy and have degenerative disc disease then adjacent segment disease is considered less likely to occur.
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