Cause
Patients who have undergone one or more operations on the lumbar spine, and continue to experience and report pain afterward can be divided into two groups. The first group are those in whom surgery was never indicated, or the surgery performed was never likely to achieve the desired result; and those in whom the surgery was indicated, but which technically did not achieve the intended result. It has been observed that patients who have a predominant painful presentation in a radicular pattern will have a better result than those who have predominant complaints of back pain.
The second group includes patients who had incomplete or inadequate operations. Lumbar spinal stenosis may be overlooked, especially when it is associated with disc protrusion or herniation. Removal of a disc, while not addressing the underlying presence of stenosis can lead to disappointing results. Occasionally operating on the wrong level occurs, as does failure to recognize an extruded or sequestered disc fragment. Inadequate or inappropriate surgical exposure can lead to other problems in not getting to the underlying pathology. Hakelius reported a 3% incidence of serious nerve root damage.
In 1992, Turner et al. published a survey of 74 journal articles which reported the results after decompression for spinal stenosis. Good to excellent results were on average reported by 64% of the patients. There was, however, a wide variation in outcomes reported. There was a better result in patients who had a degenerative spondylolisthesis. A similarly designed study by Mardjekto et al. found that a concomitant spinal arthrodesis (fusion) had a greater success rate. Herron and Trippi evaluated 24 patients, all with degenerative spondylolisthesis treated with laminectomy alone. At follow-up varying between 18 to 71 months after surgery, 20 out of the 24 patients reported a good result. Epstein reported on 290 patients treated over a 25 year period. Excellent results were obtained in 69% and good results in 13%. However, these optimistic reports do not correlate with "return to competitive employment" rates, which for the most part are dismal in most spinal surgery series.
Studies by Cohen show that up to 25% of all low back pain is sacroiliac joint in origin and that the diagnosis of sacroiliac joint disease is frequently overlooked by physicians. 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.
In the past two decades there has been a dramatic increase in fusion surgery in the U.S.: in 2001 over 122,000 lumbar fusions were performed, a 22% increase from 1990 in fusions per 100,000 population, increasing to an estimate of 250,000 in 2003, and 500,000 in 2006. In 2003, the national bill for the hardware for fusion alone was estimated to have soared to $2.5 billion a year. For patients with continued pain after surgery which is not due to the above complications or conditions, interventional pain physicians speak of the need to identify the "pain generator" i.e. the anatomical structure responsible for the patient's pain. To be effective, the surgeon must operate on the correct anatomic structure; however it is often not possible to determine the source of the pain. The reason for this is that many patients with chronic pain often have disc bulges at multiple spinal levels and the physical examination and imaging studies are unable to pinpoint the source of pain. In addition, spinal fusion itself, particularly if more than one spinal level is operated on, may result in “adjacent segment degeneration”. This is thought to occur because the fused segments may result in increased torsional and stress forces being transmitted to the intervertebral discs located above and below the fused 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.
Read more about this topic: Failed Back Syndrome