Nonetheless, the "market of the spine surgery" is growing  because patients are demanding solutions for their back problems. The tide of scientific evidence seems to go against the spinal fusions in the degenerative disc disease, discogenic pain and in specific back pain. After decades of advances in this field, the results of spinal fusions are mediocre. New epidemiological studies show that "spinal fusion must be accepted as a non proved or experimental method for the treatment of back pain". The surgical literature on spinal fusion published in the last 20 years establishes that instrumentation seems to slightly increase the fusion rate and that instrumentation doesnt improve the clinical results in general. We still are in need of randomized studies to compare the surgical results with the natural history of the disease, the placebo effect, or conservative treatment. The European Guidelines for lumbar chronic pain management show  "strong evidence" indicating that complex and demanding spine surgery where different instrumentation is used, is not more effective than a simple, safer and cheaper posterolateral fusion without instrumentation. Recently, the literature published in this field is sending a message to use "minimally invasive techniques"; – the abandonment of  transpedicular fusions. Surgery in general, and usage of metal fixation should be discarded in most cases.In Sweden, the national registry of lumbar spine surgery reported in the year 2000 that 15% of patients with spinal stenosis surgery underwent a concomitant fusion.
Followup was carried out at 3 months and one year after surgery. Pre-operative depressive disorders tended not to do well.Smoking has been shown to increase the incidence of post operative infection as well as decrease fusion rates. One study showed 90% of post operative infections occurred in smokers, as well as myonecrosis (muscle destruction) around the wound. Pathology
Before the advent of CT scanning, the pathology in failed back syndrome was difficult to understand. Computerized tomography in conjunction with metrizamide myelography in the late 1960s and 1970s allowed direct observation of the mechanisms involved in post operative failures. Six distinct pathologic conditions were identified:

Recurrent or persistent disc herniation
Spinal stenosis
Post operative infection
Epidural post-operative fibrosis
Adhesive arachnoiditis
Nerve Injury

Recurrent or persistent disc herniation
Removal of a disc at one level can lead to disc herniation at a different level at a later time. Even the most complete surgical excision of the disc still leaves 30–40% of the disc, which cannot be safely removed. This retained disc can re-herniate sometime after surgery. Virtually every major structure in the abdomen and the posterior retroperitoneal space has been injured, at some point, by removing discs using posterior laminectomy/discectomy surgical procedures. The most prominent of these is a laceration of the left internal iliac vein, which lies in close proximity to the anterior portion of the disc. In some studies, recurrent pain in the same radicular pattern or a different pattern can be as high as 50% after disc surgery.