When a surgeon chooses an operation that is not appropriate for the structural problem, the operation is likely to fail. It might prove useful, in this model, to appreciate the distinction between surgery for leg pain as opposed to surgery for back pain. True radicular (rather than referred) leg pain is usually caused by neural compression. Surgeries aimed at improving leg pain include decompression of involved neural structures in the neural foramen, central canal, or by a disk herniation. Assuming facet and SIJ source of pain have been excluded, surgeries directed toward improving axial low back pain (LBP) include fusion for pain arising from a disk (discogenic pain) or instability, for example. It follows that if a patient had predominantly axial LBP but had a decompression or discectomy without fusion, it might not have been the “right surgery” for the clinical problem, and there is a high likelihood of poor result. In other words, there was a mismatch between the clinical problem and the surgery. The surgeon performed a “leg pain operation” for LBP.

A second type of mismatch occurs when the surgery does not address all the patient’s pathology. For example, there are patients who have pathology such as disk degeneration, disk herniations, spinal stenosis, or combinations at multiple motion segments. The surgeon might have elected to operate on only the worst segment or segments, thereby leaving the patient with residual problems at the adjacent segments. This type of patient might have required multilevel surgery or, if the number of levels is excessive, perhaps no surgery at all.

Another example is the patient with both central and foraminal stenosis. The surgeon achieves decompression of the central canal but does not achieve adequate decompression of the lateral canal. The patient may be left with leg pain due to remaining foraminal stenosis, which might incorrectly be thought to be neuropathic pain. Yet, another example is the patient with severe foraminal stenosis. A surgeon may decide to perform a limited decompression for fear of causing instability that might necessitate fusion. As a result, there is inadequate decompression and the patient does not get better. The patient needed decompression and fusion but only had decompression. This is another mismatch between the surgery needed and the surgery performed.

Another example of a mismatch between the surgery needed and the surgery performed occurs when the surgeon fails to fully consider the effect of surgery on the motion segment. For example, consider a patient with spinal stenosis and very slight spondylolisthesis and spinal stenosis who has leg pain. If the surgeon chooses decompression without fusion, many times, the spondylolisthesis progresses and the patient develops progressive LBP.

Finally, and not to be minimized, some spinal pathology is not treatable by surgery. An example would be four or five levels of painful disks.

If a patient has not been fully evaluated, it is more likely that the surgery will fail. Surgery performed after an incomplete evaluation might leave significant structural pathology unattended.
Incomplete evaluation is often due to over reliance on imaging studies, particularly magnetic resonance imaging (MRI), without fully appreciating the information from the history and examination. Many spine specialists use confirmatory diagnostic spinal injections to complement the other information. Plain radiographs done standing with flexion and extension views can be very valuable to disclose spondylolisthesis or deformity that was not seen on supine MRI.⁸ Pain relief after transforaminal epidural injection would suggest any foraminal stenosis seen on MRI is in fact the pain generator.^9,10,11 Discography had been used frequently but is rarely used now due to the possibility of creating long-term degeneration of otherwise normal disks coupled with the great improvements in the quality of MRI scans.¹²

Psychological health is one of the most important variables with respect to the outcome of surgery.^13,14 Therefore, psychological evaluation is especially important for patients (“right patient”) with long-standing pain and impairment or when the surgeon has any inkling that there might be a significant psychological problem. Neither surgeons nor physiatrists perform well in identifying patients with psychological illness compared to objective psychological testing and so referral is often in the best interests of all.¹⁵

Most psychological illness in the postoperative patient was present before surgery but not considered or was underestimated. Many patients with long-standing chronic LBP have some degree of psychological illness, some mild but some more severe, which might have altered surgery decision making.¹³ The most common problems described are depression, anxiety disorder, and substance use disorder.¹⁴ Although these disorders may not be a contraindication for surgery, treatment before surgery and psychological follow-up afterward might prove useful to increase the chances of a good result. In addition to these familiar illnesses, there is growing evidence that a patient’s coping abilities, fear and fear-avoidance behavior, and history of sexual or physical abuse may play important roles in continuing pain, impairment, and disability and contributing to a poor outcome.^{16,17,18,19,20,21,22,23}

Even though the surgery was appropriate for the symptoms and pathology, the surgeon may not have accomplished the technical goals. Technical failure is usually apparent on good-quality imaging studies. Inadequate decompression of a foramen is not uncommon. There may be incomplete removal of a disk herniation, especially if it was a far lateral herniation. There may be misplacement of screws or incorrect connection of internal fixation.

Recurrent pathology can recur even after perfect surgery. Disk herniations recur in up to 15% of patients after discectomy. Foraminal stenosis can recur after if there is progressive degeneration of the same motion segment.

Pain after prior spine surgery may be totally unrelated to the index surgery. The usual structural causes of LBP can occur after an index surgery.

Foraminal stenosis was found in 15% and 35% of FBS patients in the studies of Waguespack et al.⁵ and Slipman et al.,⁶ half of what was seen 25 years ago.⁴ The lower prevalence may be due to increased awareness of the problem, improved imaging studies, and/or better understanding of the need for meticulous decompression. Patients with foraminal stenosis have pain that is predominantly in the leg or buttock region, often in the distribution of a single dermatome. Pain is usually worsened by standing and walking and relieved by sitting. MRI or CT scan shows narrowing of the canal at the index level or an adjacent segment.

There are no data regarding the utility of selective nerve root blocks in FBS. There are suggestions that when performed with excellent technique, they can provide some information, especially perhaps when there is no relief, which might suggest the targeted root was not the cause of pain.¹⁰ According to one systematic review, there is good evidence that lumbar
selective nerve root blocks can aid with the identification of one or more symptomatic roots.⁹ There is moderate evidence that identifying or excluding a root as cause of pain improves surgical outcome.⁹ Other systematic reviews did not find the evidence convincing.¹¹

Pain that arises from within a disk is often referred to as discogenic pain. One or more painful disks was found to be the cause of FBS in 25% to 30% of patients.^4,5,6,7 Painful disks can occur at the level of prior surgery, at an adjacent segment, or rarely at the index level despite prior posterolateral fusion.^34,35 When there is a residual painful disk at the index surgical level, it is likely that it was not treated adequately by performing a fusion, especially an interbody fusion. When there is a painful disk at an adjacent segment, it was either present prior to surgery and not addressed or the disk degenerated after surgery.³⁵ Risk factors for adjacent segment degeneration include body mass index >25 kg/m, preoperative disk degeneration, and superior FJ violation during surgery

Although there is no totally consistent symptom complex for discogenic LBP, especially after surgery, the diagnosis is more likely when there is dominant midline LBP that might radiate to the left and right of the midline, the gluteal regions, and often to the leg in a nondermatomal fashion. Pain is usually worse sitting and during transition from sitting to standing. It may improve with standing or walking. Physical examination is not specific. There may be decreased flexion in standing due to pain. There may be tenderness over the spinous processes but not over the FJs.

When the diagnosis of discogenic pain is suggested by history and examination, MRI shows a single degenerated disk, and other potential causes of chronic LBP have been excluded, it is likely that the diagnosis is correct.

Recurrent or residual disk herniation was seen in 7% to 12% of patients with FBS.^4,5,6 There are two common presentations of pain from a disk herniation: radicular and axial. The topography of the pain is primarily due to the location of the herniation. A posterolateral herniation is more likely to compress or irritate a nerve root and therefore present with predominant leg pain. A midline herniation, unless very large, does not compress neural elements and presents with predominant LBP. A disk that is degenerated and herniated can cause both leg pain and LBP. In the presence of epidural or perineural fibrosis, a disk herniation may cause more leg pain than expected than if there were no fibrosis.