Lumbar surgery with or without bone grafts and with or without implanted hardware can be controversial when employed for treating chronic pain alone. Radiologic studies have shown that 80% of asymptomatic individuals have evidence of degenerative disk disease or a bulging or herniated disk,²¹ conditions often considered an indication for surgery. Yet, no clear indicators currently exist to determine which patients with low back pain would benefit from surgery.²² In the United States, rates of spine surgery for back and leg pain have been steadily increasing, and there is a wide variation of the frequency of back surgery from one region of the country to the next.²³ Outcome trials of surgery for individuals with chronic low back pain have indicated success rates that range between 41% and 57%.²⁴ A number of controlled trials, however, have indicated that surgery is no better than physical therapy and multidisciplinary rehabilitation.^{25,26,27,28,29} A troublesome component of back surgery is postsurgical complications and increased pain. Rates of complications and reoperations after spine surgery have ranged from 5% to 16%.²⁴

Deyo and Mirza,³⁰ found that 2 years after surgery, there was no significant difference between back pain patients of similar diagnosis who were treated surgically or nonsurgically. Turner et al.,³¹ reviewing all published research on spinal fusion, found that approximately 65% to 75% of all patients achieved satisfactory clinical outcomes. In these studies, poorer outcome was associated with a number of factors, including greater numbers of fused levels and the use of instrumentation. Similarly, Hoffman and colleagues,³² in a literature review on laminectomy and discectomy, found that the mean success rate of these procedures for relief of spine pain was 67%. The popular media have highlighted these and similar results, which appear to provide support for declarations about treatments for
back pain such as that of a recent issue of Consumer Reports (June 2017) that stated “conventional approaches don’t always work and can cause other serious problems.”

Failed spine surgery can significantly impact the patient, the physician, the employer, and the third-party payer. The patient often continues to remain disabled, with perhaps even greater pain, increased medication dependence, and more emotional difficulty than prior to the surgery. The pain may be so great, or the surgery so unsuccessful, that reoperation is required, as is the case in an estimated 10% of those who undergo laminectomy and discectomy,³² and 23% of those who undergo spinal fusion.³¹ The patient after failed surgery places many demands on the health care system, often requiring increasing medications and multiple additional treatments. Patients often feel frustrated and discouraged. The physician may become angry with the patient for not responding to treatment and the employer can be concerned about his or her obligation to pay compensation to a permanently disabled worker.

Given that spine surgery can be effective yet the implications of failed spine surgeries can be so profound, it becomes critical to determine factors that may lead to poor results from such procedures. Improper pre- and postoperative information and treatments may also worsen surgical results. A growing body of research indicates that psychosocial factors are among the most significant influences on spine surgery results. For example, DeBerard et al.³³ compared the outcomes of spinal fusion in patients who had been recommended for a preoperative psychological evaluation (based on surgeon recognition of the presence of psychosocial concerns) versus those who were not recommended for such evaluations. Those recommended for a psychological evaluation did less well after surgery, suggesting that even the surgeons’ perception of psychological issues was predictive of outcome. In another study, DeBerard and colleagues³⁴ demonstrated that those who were identified with more negative affect (high psych) before back surgery had more repeat surgeries, had greater disability, had higher medical expenses, and had a higher incidence of disability after surgery than those with less emotional distress. Thus, presurgical evaluation and careful patient selection can be extremely important in helping to identify those individuals who might benefit the most from lumbar surgery.

SCS with implantable or externalized systems has been available since the 1960s.³⁵ The theoretical basis of the efficacy of SCS is based on Melzack and Wall’s³⁶ gate control theory that proposes that stimulation of large nerve fibers overrides the transmission of small nerve fibers that transmit pain. SCS is expected to reduce, not eliminate pain by blocking the conduction of primary nerve pathways.³⁷ It seems to be most successful in relieving pain in the limbs (e.g., the leg or arm), although more recently, neurostimulation devices have been developed that target axial back pain.^38,39 Throughout the years, there have been improvements in SCS systems allowing for better coverage of painful areas with multiple channels, higher frequency stimulation, burst technology, electrode surfaces with increased number of contacts, and leads that are shaped to provide varying degrees of coverage.⁴⁰ Spinal cord stimulators have reported success rates ranging from 20% to 70%.⁴¹ They have been found to be efficacious for neuropathic pain⁴² and radiculopathy.⁴³ There has been a rapid increase in the number of implanted spinal cord stimulators, and some econometric analyses have indicated that SCS may be a cost-effective treatment option, particularly for patients with persistent neuropathic pain syndromes and complex regional pain syndrome.⁴⁴

Spinal infusion of analgesics, with use of an IDDS has been utilized since the 1980s.⁴⁵ Spinally administered analgesics had initially been used for treatment of cancer pain⁴⁶ and with the subsequent development of implantable components for continuous intrathecal infusions became an acceptable method to treat patients with intractable spasticity as well as pain.⁴⁷ This technology consists of implanting a drug delivery device designed for long-term continuous infusion of medication. The drug delivery system consists of a collapsible drug reservoir into which the drug is injected and, powered by a battery and computer chip, allows for variable infusion rates and bolus injections through a catheter anchored in the back with the tip of the catheter positioned within the thecal sac to deliver drug to the cerebrospinal fluid (CSF).⁴⁸ Such infusions for cancer pain have good success rates (defined as a reduction of pain by one-third), ranging from 60% to 90%.⁴⁹ Collectively, intrathecal infusion devices have provided pain relief in noncancer pain patients who had failed more conservative therapies⁵⁰ and patients with an IDDS have demonstrated a reduction in side effects from oral medications, decreased need for oral analgesia, and improvement in their physical assessment.⁵¹ The data indicate variable success rates for noncancer pain ranging from 25% to 70%.⁵²

Although outcome studies report that SCS and/or an IDDS are efficacious in treating chronic pain, decisions for implantation have historically been based on clinical judgment of the implanting physician.⁴⁹ Recent empirical work, though, has begun to investigate the clinical characteristics that are associated with outcomes for implantable devices. A study by Hassenbusch and colleagues⁵³ compared SCS with intrathecal infusions by measuring postoperative verbal numeric scores and activity levels. The findings of this study and others suggest that IDDS were useful in reducing bilateral or axial pain (e.g., pain just in the low back), whereas SCS is better for unilateral radicular symptoms (e.g., pain down one leg stemming from nerve damage in the back).⁵⁰ In general, patients considered for an implantable device often are not seen as poor candidates for spinal surgery, either due to previous failed surgery or lack of clear pathology accounting for the pain, and have failed to respond to conservative approaches and long-term use of oral opioids.

Implantation of these devices, however, is not without risks. Reports of infection or intrathecal granulomas causing neurologic injury are documented,⁵⁴ and the safety of these devices for use with chronic noncancer pain patients is an important consideration. The risks associated with SCS include possible nerve injury, spinal cord puncture, bleeding, and infection. Similar risks also exist for IDDS including discomfort at the implantation site as well as possible disconnections, kinking, catheter migration, and inflammatory masses (granulomas) that build up at the tip of the catheter. Risks also include increased depression if the device becomes ineffective in reducing pain.⁴⁸ Because of the risks associated with implantation of these devices, as well as their substantial costs, there has been a good deal of emphasis on patient selection. As noted earlier, some studies have focused on identifying pain phenotypes that are most responsive to implantable therapies^48,53; other areas of investigation include evaluation of psychosocial factors that might predict success or failure of stimulators or IDDS. Thus, a careful evaluation of each candidate for surgery or for an implantable device is judged to be important, and in clinical practice, a psychological evaluation is often a recommended or mandatory part of the evaluation process for patients being considered for implantable pain-management devices.

Many chronic pain patients experience some level of depression. For up to 85%, the intensity of this emotional experience is sufficient to meet the diagnostic criteria for clinical depression.¹⁷ Depressive symptoms include depressed mood, diminished interest in almost all activities, weight loss or gain,
insomnia or hypersomnia, agitation or psychomotor retardation, fatigue or energy loss, feelings of worthlessness or guilt, impaired concentration, and recurrent thoughts of death unrelated to other comorbidities.⁵⁵ Several studies have assessed depression using different instruments and found that it can be predictive of greater disability and poor outcomes of spinal surgery.⁵⁶ Kjelby-Wendt et al.⁵⁷ examining discectomy results found that patient satisfaction with surgery was strongly related to elevated scores on the Beck Depression Inventory (BDI)—in fact, elevated scores were found in 55% of dissatisfied patients but in only 18% of satisfied patients. Schade et al.⁵⁸ found that depression, as assessed on a simple Likert-type scale, had strong negative correlations with return to work and overall recovery. Trief et al.⁵⁹ found that high scores on the Zung depression inventory were associated with little reduction in back pain and elevated work disability after spine surgery. Finally, DeBerard et al.³⁴ found that depression was strongly related to total medical costs in workers’ compensation patients undergoing spinal fusion.

Patients with chronic pain and a comorbid psychiatric disorder are more likely to report greater pain intensity, more pain-related disability, and a larger affective component to their pain than those without psychiatric comorbidity.^60,61 Patients with chronic pain and psychopathology, especially those with chronic low back pain, also typically have poorer pain and disability outcomes with treatment.^62,63,64 There is a significantly poorer return-to-work rate 1 year after injury among patients with chronic pain and anxiety and/or depression compared with those without any psychopathology.⁶⁵ Thus, psychiatric comorbidity, primarily major depression and anxiety disorders, is associated with greater levels of chronic pain, more disability, and a worse response to treatment.

Given the significant interpatient variability in treatment outcomes, it would be of tremendous value, from both a societal and patient perspective, to identify in advance who is most and least likely to benefit from surgery or an implanted device. In general, some risk factors have been identified that correlate with greater risk for pain or poor outcomes from treatment for pain. These include variables such as pain chronicity, psychological distress, a history of abuse or trauma, poor social support, and significant cognitive deficits.⁶⁵ In particular, psychopathology and/or extreme emotionality have been seen as contraindications for certain therapies.⁶⁶ Outcome studies highlight the poor response of patients with psychiatric comorbidity to many treatments.^67,68 For example, spinal pain patients with both anxiety and depression have a 62% worse return-to-work rate than those with no psychopathology.⁶⁹ Epidemiologic research suggests a bidirectional association between back pain and emotional distress; pain increases symptoms of depression and individuals with a preexisting depressive disorder have a disproportionately high risk for developing spinal pain.⁷⁰ Similarly, cognitive processes such as maladaptive beliefs and pessimistic expectations are associated with a greater likelihood of developing chronic pain and with poorer functional outcomes among chronic low back pain patients.⁷¹ There is also evidence of a genetic predisposition toward increased depression and anxiety among persons with low back pain based on twin studies.⁷²

Numerous factors are likely to play a role in shaping outcomes following surgical interventions or placement of an implanted device in patients with chronic back pain. However, there does not seem to be a consensus on what factors are the strongest and most consistently predictive of outcomes, and there is no universally accepted standard approach for screening surgical candidates or individuals considered for an implanted device. Nonetheless, a presurgical psychological evaluation is often recommended based on research demonstrating the predictive value of spine presurgical psychological evaluations.⁷³

A recent systematic review was carried out of the current literature, using critical appraisal and strategies to limit bias, to determine the strength of the evidence for the assumption that careful screening will help to predict pain-related and functional outcomes from lumbar surgery or SCS.⁷⁴ Collectively, a statistically significant relationship was found between psychological factors and treatment outcome (e.g., high preimplant levels of distress were prospectively associated with less SCS-related pain relief) in 92% of the studies reviewed. In particular, presurgical somatization, depression, anxiety, and poor coping were most useful in helping to predict poor response (i.e., less treatmentrelated benefit) to lumbar surgery and SCS. Older age and longer pain duration were also predictive of poorer outcome in some studies, whereas pretreatment physical findings, activity interference, and pain intensity were minimally predictive. Interestingly, several studies have confirmed that younger patients treated earlier in the course of their pain condition derive the most benefit from SCS,⁷⁵ which might suggest that using SCS as a “last resort” could be a suboptimal management strategy.

A review of psychosocial characteristics as predictors of outcomes following SCS suggests that depression is most robustly linked to poor SCS outcomes.⁷⁶ Indeed, Sparkes and colleagues⁷⁶ cite multiple well-designed studies suggesting that higher levels of preimplantation depressive symptoms impact negatively on the efficacy of SCS treatment.

Trief and colleagues⁵⁹ found that patients with elevated state anxiety scores on the State Trait Anxiety Inventory (STAI) achieved less pain relief and lower return to work rates after surgery than did patients with lower anxiety. One particularly troublesome type of anxiety centers on the belief that increasing function and activity may increase the likelihood of reinjury. This type of fear measure has been assessed by several questionnaires including the Tampa Scale for Kinesiophobia.⁷⁷ Den Boer et al.⁷⁸ found that elevated scores on the Tampa scale were associated with delayed return to work after lumbar disk surgery. One plausible explanation for this result is that patients with a heightened fear of movement might be less likely to engage in aggressive postoperative rehabilitation. Kiecolt-Glaser et al.⁷⁹ suggest that anxiety may increase postoperative pain and such increased noxious sensations could then downregulate immune function, further compromising the surgery healing process.

Estimated rates of chronic pain patients with somatization (sometimes known as hypochondriasis) vary, ranging from 1% to 12%, even though unexplained symptoms are a common problem in medical settings.^80,81 The classical concept of somatization that implies that there is no pathophysiologic basis for physical complaints is quite problematic to apply to patients with chronic pain. This is because the majority of patients with chronic pain have some underlying physical condition that is at least partially responsible for their pain. The pain symptoms due to a physical or somatic cause (such as degenerative disk disease in the lumbar spine) may then be amplified by psychiatric factors, such as depression, anxiety, pain catastrophizing, fear of movement, and/or poor coping.⁸² Areas in the brain which process pain and mood together (such as the prefrontal and anterior cingulate cortices, and insula, commonly termed the medial pain system) may be the underlying brain substrates by which pain signals coming from the spinal cord are then amplified and perceived as heightened pain sensations. Hence, it is more appropriate to think of somatization as a process of amplification of bodily signals centered in the brain. There may or may not be a physical basis in the body for the abnormal physical sensations.⁸³ The “somatoform pain disorders” fall within the “Somatization Disorders” classification in Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-5) and are meant to capture this concept of amplification of bodily
perceptions, which is made worse by concomitant depression. The two diagnoses most commonly used with chronic pain patients are Pain disorders associated with psychological factors and a general medical condition, and Pain disorders associated with psychological factors. For patients with a strong component of heightened awareness of pain, the evidence is strong that repeated invasive procedures and implanted devices almost uniformly are unsuccessful.^61,74 Education about the nature of the problem and helping patients understand the risk associated with repeated treatments is also important.

Providers should resist a dualistic model that postulates that pain is either all physical or all mental in origin. This model alienates patients who may feel blamed for their pain and is not consistent with modern models of pain causation. Multiple lines of evidence suggest that pain is a product of efferent as well as afferent activity in the nervous system. We know that tissue damage and nociception are not necessary or sufficient for pain and the relationship between pain and nociception is highly complex. We are only beginning to understand the complexities of the relationship between pain and suffering, which appears to be a central phenomenon.⁸⁴

Recent studies have also suggested that quantitative sensory testing (QST) may be a useful adjunct to psychological evaluation in the assessment of patients under consideration for spinal surgery or for placement of an implantable device. QST involves the administration of standardized noxious stimuli under highly controlled conditions; often, parameters such as pain threshold and tolerance in response to a variety of stimulus modalities are measured as indices of pain sensitivity. Our group recently reported that high levels of pain sensitivity may be associated with elevated risk for pain medication misuse⁸⁵ and individual differences in QST responses may be useful as prognostic indicators in a variety of settings. For example, among neuropathic pain patients undergoing SCS, the degree of pretrial mechanical allodynia was inversely associated with the amount of pain relief reported by patients.⁸⁶ That is, the most mechanosensitive patients reported the least SCS-related analgesic benefit. Functional neuroimaging studies have revealed that SCS functions in part by activating cortical pain-modulatory circuitry,⁸⁷ and it may be that the most preoperatively pain-sensitive individuals are those whose pain-modulatory systems are the most difficult to engage. Patients with chronic low back pain exhibit generalized patterns of hypersensitivity to pain that are consistent with central sensitization-like processes,^88,89,90 indicating that heightened pain sensitivity in the central nervous system may represent an important pain mechanism in patients with chronic back pain.

Assessment of pain sensitivity is potentially useful in several surgical contexts. First, there is some evidence that a higher degree of preoperative pain sensitivity is associated with poorer pain and disability outcomes following spinal surgery.^91,92,93 Such findings are consistent with data from other surgical procedures indicating that preoperative sensory phenotyping with QST can provide valuable prognostic data.^94,95 Second, assessment of sensory responses to provocative tests such as discography, which involves injection of radiographic dye into the nucleus pulposus of a putatively disrupted disk, can be illuminating. The injection, performed under fluoroscopy and combined with postdiscogram CT, gives evidence of the presence and extent of disk disruption. Interestingly, the injection of a disrupted disk has been demonstrated to act as a stimulus that provokes pain, often with a pattern and intensity similar to the patient’s normally occurring pain. For example, Vanharanta et al.⁹⁶ found that injection of moderately to severely disrupted disks provoked pain that was similar or an exact reproduction of normally occurring pain in approximately 65% of cases. On the other hand, injection into normal-appearing disks provoked exact or similar reproduction of pain in only 18% of cases. Even stronger results along the same lines were obtained by Walsh et al.⁹⁷ Thus, discography may provide a laboratory method for administering controlled stimulation of the disk in order to assess whether certain patients with low back pain display heightened pain sensitivity.

Anger is a common and prominent emotion in patients with chronic pain. Patients with low back pain, in particular, may experience and express anger about past medical care; about unfair treatment by employers, friends, and family; and about the physical and functional limitations that are endemic to low back pain.⁹⁸ A study by Fernandez and Milburn⁹⁹ demonstrates just how frequently patients experience this emotion. These researchers asked chronic pain patients to endorse the intensity of 10 different emotions they were experiencing and found that anger was given the highest ratings of all emotions assessed.⁹⁹ High levels of anger have also been associated with postoperative complications and elevated levels of postoperative pain for spinal surgeries as well as other procedures.¹⁰⁰ There are numerous reasons why anger may have a negative impact on pain-related outcomes. First, anger may lead to maladaptive lifestyle changes, such as poor health habits, lack of physical exercise, or excessive use of drugs or alcohol. Such poor health behavior profiles may impair the benefits of physical interventions and have a negative impact on the patient’s commitment to postoperative rehabilitation. Second, anger can lead to the desire for vindication or revenge, and certainly, this can influence treatment results.^101,102 Similarly, DeGood and Kiernan¹⁰³ have found chronic pain patients who are angry and blame their employer for their injuries report high levels of emotional distress and have poorer response to treatment. Third, anger has been shown to have an adverse effect on many health conditions, such as cardiovascular disease, headaches, asthma, and many others, which may in turn exacerbate the negative effects of pain.¹⁰⁴ Final, anger appears to directly impact physiologic pain perception by increasing muscle tension near the site of the injury, activating neural circuits underlying regulation of pain, and interfering with the analgesic effects of endogenous opioids.^105,106