vertebrae. This pathology is one reason behind the development of artificial discs as a possible alternative to fusion surgery. But fusion surgeons argue that spinal fusion is more time-tested, and artificial discs contain metal hardware that is unlikely to last as long as biological material without shattering and leaving metal fragments in the spinal canal. These represent different schools of thought. (See discussion on disc replacement infra.) Another highly relevant consideration is the increasing recognition of the importance of "chemical radiculitis" in the generation of back pain. A primary focus of surgery is to remove "pressure" or reduce mechanical compression on a neural element: either the spinal cord, or a nerve root. But it is increasingly recognized that back pain, rather than being solely due to compression, may instead entirely be due to chemical inflammation of the nerve root. It has been known for several decades that disc herniations result in a massive inflammation of the associated nerve root. In the past five years increasing evidence has pointed to a specific inflammatory mediator of this pain. This inflammatory molecule, called tumor necrosis factor-alpha (TNF), is released not only by the herniated or protruding disc, but also in cases of disc tear (annular tear), by facet joints, and in spinal stenosis. In addition to causing pain and inflammation, TNF may also contribute to disc degeneration. If the cause of the pain is not compression, but rather is inflammation mediated by TNF, then this may well explain why surgery might not relieve the pain, and might even exacerbate it, resulting in FBSS. Role of sacroiliac joint (SIJ) in lower back pain (LBP) A 2005 review by Cohen concluded,'The SI joint is a real yet underappreciated pain generator in an estimated 15% to 25% of patients with axial LBP'. Studies by Ha, et al., show that the incidence of SI joint degeneration in post-lumbar fusion surgery is 75% at 5 years post-surgery, based on imaging. Studies by DePalma and Liliang, et al., demonstrate that 40–61% of post-lumbar fusion patients were symptomatic for SI joint dysfunction based on diagnostic blocks. Smoking Recent studies have shown that cigarette smokers will routinely fail all spinal surgery, if the goal of that surgery is the decrease of pain and impairment. Many surgeons consider smoking to be an absolute contraindication to spinal surgery. Nicotine appears to interfere with bone metabolism through induced calcitonin resistance and decreased osteoblastic function.