A study by Waguespack (et al, 2002) outlined the most common causes of failed back surgery syndrome (FBSS) in a group of 181 patients with the condition. In 6% of the patients the cause of FBSS remains unknown. The largest group by far, at 29%, included those patients who continued to suffer from foraminal stenosis and spinal stenosis with inadequate decompression or resulting spinal disc instability following surgery. Bulging discs or herniation along with inadequate opening up of the foramina allowed nerve compression to continue in these patients and usually required further back surgery following an MRI or CT scan.
FBSS Caused by a Fusion
The second major reason for FBSS was painful disc disease from the continued motion of the discs above or below the surgical fusion site. This complication, present in 16.9% of the group, may be prevented through the use of discography to determine the level of degeneration in the discs adjacent to the site at which surgery is being contemplated. Surgery can then, accordingly, be altered to reduce the extra pressure which would have been put upon these levels. Pseudoarthrosis, or failure to form a solid union following spinal fusion, was the next most common cause of failed back surgery syndrome with 14.8% of the 183 patients experiencing this outcome. Excessive disc motion or the rubbing of bone against bone is responsible, for the most part, for the pain from pseudoarthrosis with failure of fusion attributed to smoking, NSAID use, inadequate stabilization during surgery, and other complications. Patients may be treated through additional surgery in some cases.
Neuropathic causes of FBSS
Neuropathic causes, including peridural (epidural) fibrosis or scarring, accounted for 9.3% of the cases of FBSS. With subsequent surgery the risks of FBSS due to neuropathic causes is more than 60%. Recurrent disc herniation accounted for 6% of the cases, and spinal instability for 4.9% where too much structural material was removed, including disc material, spinal ligaments, and the facet joints. Patients who had surgery at multiple levels but received no spinal fusion often had to undergo fusion at a later date. The remaining 14% or so of reasons behind failed back surgery syndrome are split between painful discs in addition to stenosis (4.4%), painful discs within fusion (2.7%), psychological reasons (2.7%), infection (1.6%), recurrent disc herniation with stenosis (1.6%), and arachnoiditis (1.1%).
Numerous other studies have found wildly varying degrees of failed back surgery syndrome due to these reasons, with some putting epidural fibrosis at 25% and others claiming that psychological factors such as job dissatisfaction play a much larger role in the continuation of back pain after surgery (Gasiński, et al, 2000, Mielenz, et al, 2008).
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