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.
Neoplasia also includes direct seeding of the cerebrospinal fluid (CSF) from primary central nervous system (CNS) tumors such as glioblastoma multiforme, medulloblastoma, ependymoma, and choroid plexus carcinoma. Strictly speaking, the most common cause of arachnoiditis in failed back syndrome is not infectious or from cancer. It is due to non-specific scarring secondary to the surgery or the underlying pathology. Nerve injury
Laceration of a nerve root, or damage from cautery or traction can lead to chronic pain, however this can be difficult to determine. Chronic compression of the nerve root by a persistent agent such as disc, bone (osteophyte) or scarring can also permanently damage the nerve root. Epidural scarring caused by the initial pathology or occurring after the surgery can also contribute to nerve damage. In one study of failed back patients, the presence of pathology was noted to be at the same site as the level of  surgery performed in 57% of cases. The remaining cases developed pathology at a different level, or on the opposite side, but at the same level as the surgery was performed. In theory, all failed back patients have some sort of nerve injury or damage which leads to a persistence of symptoms after a reasonable healing time. Diagnosis
Avoiding post-laminectomy/laminotomy syndrome
Smaller procedures that do not remove bone (such as Endoscopic Transforaminal Lumbar Discectomy and Reconfiguration) do not cause post laminectomy/laminotomy syndrome. Management
Failed back syndrome (FBS) is a well-recognized complication of surgery of the lumbar spine.