Introduction
Chronic low back pain represents a significant burden to the United States. Approximately 37% of the general adult population suffers from low back pain with an estimated cost of 12.2 to 90.6 billion US dollars per year. The number of spine surgeries has steadily increased in the past several decades, with an increase in elective lumbar fusions of 62.3% between 2004 and 2005. Consequently, the incidence of failed back surgery syndrome (FBSS) has been increasing. FBSS is defined as recurring or persistent back pain following one or more spinal surgeries. An incidence of 10% to 40% is commonly noted in patients who have undergone lumbosacral spinal surgery. Treatment has historically included conservative management, reoperation, and spinal cord stimulation (SCS). Repeat spinal surgery results in diminishing returns with an initial success rate of 50%, but not more than 30%, 15%, and 5% experience a successful outcome after the second, third, and fourth surgeries, respectively. Despite advances in surgical techniques and technology, the rates of FBSS remain similar to several decades ago. In the setting of limited success of repeat spinal surgeries and issues with opioid use for chronic pain management, the role of alternative interventions has become increasingly important. Epidural electrical stimulation of the dorsal column, commonly referred to as SCS, has emerged as a vital tool in the management of chronic low back pain and represents an opportunity for surgeons to expand their scope of practice to better treat their patients. However, despite its emerging role, there are some barriers to its adoption which we will address in this chapter.
Why Spinal Cord Stimulation?
“When you have a hammer, everything looks like a nail.” This is an adage that surgeons often begrudgingly acknowledge. Thus, in difficult-to-treat chronic pain patients and to prevent this axiom from becoming reality, multidisciplinary review of cases may be exceptionally helpful. Although obtaining imaging after a repeat spine surgery and offering correction of any radiographic abnormality that has a clinical correlate are no doubt standard, the surgeon must essentially remember the impetus for the procedure prior to embarking on such surgery. If the patient has pain but no instability, evidence of instrumentation malfunction, or new pathology, the type of pain should be explored. Often neuropathic pain will not respond to further spine surgery, and in those cases, SCS should be considered.
When presenting neuromodulation options to spine surgeons or primary care physicians, we often hear “Those devices do not work.” The reasons for this bias are complicated. For many years, the expected outcome was “50% improvement for 50% of patients.” Kumar et al. demonstrated this to be the case. In their landmark paper, they compared the efficacy of conservative medical management (CMM) combined with SCS with CMM alone. One hundred FBSS subjects with predominant radicular leg pain of neuropathic origin were randomly assigned to either group. The primary outcome was defined as the proportion of subjects who had at least a 50% reduction in leg pain. Secondary outcomes were improvements in back and leg pain, health-related quality of life, and functional capacity; decreased use of pain medications and other treatments for pain; level of subject satisfaction; and incidence of complications and adverse events. At 6 months, 48% of SCS subjects and 9% of CMM subjects had at least a 50% reduction in pain ( P < .001).
SCS outcomes have continued to improve, and patients who benefit now include those without leg pain. Kapural et al. found that the rate of response following SCS surgery for limb pain was 83.1% at 3 months. Even more relevant, they also found that 84.5% of patients receiving SCS for the indication of back pain were responsive to the treatment, which is a significant departure from stereotypes in much of the medical literature. Notably, these impressive response rates to SCS were found in subjects receiving 10 kHz high-frequency stimulation (HF10; Senza System, Nevro Corp., United States); their counterparts receiving an older tonic SCS system (Precision Plus System, Boston Scientific, USA) had much lower response rates, reported as 43.8% for back pain and 55.5% for limb pain. Therefore, although the original SCS devices may have offered superior relief of limb pain at that time, newer systems are providing even better outcomes” as it the programming options are largely what have changed, not the perc/paddle implants themselves. Additionally, in a study by Khan et al., 22% of patients receiving SCS actually had pain remission after SCS (i.e., experienced >80% pain relief as measured by improvement on their preoperative to postoperative numeric rating scales).
When making a decision between SCS and spine revision surgery, the spine surgeon must consider the patient’s goal with surgery. Is the purpose of the surgery to reduce pain, or to correct an anatomical deformity that may or may not be the cause of the pain? The literature demonstrates overwhelmingly positive evidence for the use of SCS over other treatment modalities for the reduction of pain. In a prominent randomized control trial, North et al. compared the efficacy of repeat lumbosacral spinal surgery with SCS. Some 50 FBSS subjects who met the criteria for surgical intervention were randomized to receive either repeat surgery or a spinal cord stimulator. Crossover between the groups was permitted after 6 months if the results were unsatisfactory. Success was based on at least a 50% reduction in pain and subject satisfaction with treatment. Of the 45 subjects available for follow-up, a 47% (9 of 19) success rate was seen in subjects who received SCS versus 11.5% (3 of 26) of subjects who received repeated lumbosacral spine surgery ( P <.01). Moreover, the subjects initially randomized to SCS were significantly less likely to cross over than those assigned to reoperation ( P =.02). The subjects in the reoperation group were also noted to require more opioid analgesics than the SCS group ( P <.025). This study was the first randomized controlled trial to demonstrate the superiority of SCS over spinal reoperation. The overall success and benefit were noted to be less in the subjects who crossed over into the SCS group following reoperation. Interestingly, subjects in the Khan et al. study who were receiving opioid therapy or experiencing disability prior to receiving SCS were less likely to be remitters, supporting that SCS should be considered as a first-line therapy instead of as a last-ditch attempt at pain relief. We appreciate that what we are recommending is a paradigm shift. Specifically, spine surgeons must be open to the possibility that their patient may be more likely to achieve their goals from an SCS than from a revision fusion.
In summary, the mantra that SCS treats leg pain but not back pain is no longer the case. Efficacy rates for SCS have improved over time with changes in technology. Currently, over 80% of patients are responders, response rates exceed 50%, and almost 20% of patients actually have pain remission. This is a far cry from the outcomes of the late 1990s/early 2000s, when only 50% of patients had desired outcomes. Furthermore, in the past, good patient outcomes were commonly misinterpreted as a poor response on the basis of any residual pain.
What Therapy Is More Cost-Effective?
In 2002, Kumar et al. monitored 104 FBSS subjects (60 with SCS and 44 with CMM) for 5 years, collecting data about the total cost of care, quality of life, and ability to return to employment. Although the cost of treatment for the SCS group was greater than that for the CMM group in the first 2.5 years, the mean cumulative cost for SCS therapy thereafter was significantly less (29,123 Canadian dollars per subject, compared with 38,029 Canadian dollars per subject for CMM at 5 years). The higher costs of the CMM group were associated with medications, ongoing physician visits, radiographs, and emergency visits. Additionally, 15% of the subjects in the SCS group were able to return to work compared with none in the CMM group. The return-to-work status afforded by SCS offers societal benefit and decreases the economic impact of chronic back pain. Additionally, SCS has been demonstrated to be more cost-effective than reoperation. North et al. compared the cost of SCS with reoperation and found that SCS led to lower costs for patients with FBSS, with SCS patients spending an average of 31,530 US dollars versus 38,160 US dollars for patients receiving reoperation. Additionally, the total mean cost for reoperation was reported to be 28,019 US dollars for lumbar disc herniation, compared with 13,135 US dollars for nonoperative patients.
More recently, Kumar and Rizvi compared the cost-effectiveness of SCS plus CMM with CMM alone. Markov models were developed to evaluate the costs and effects over a 20-year time horizon. The incremental cost-effectiveness of SCS was 9293 Canadian dollars per quality-adjusted life year (QALY) gained, with a 75% likelihood that SCS would be more effective than CMM. The cost difference was 12,297 Canadian dollars over 20 years with a gain of 1.39 QALYs in the SCS group. The outcomes of these models suggested that SCS was highly cost-effective compared with CMM alone. Using the safety, appropriateness, fiscal neutrality, and effectiveness (SAFE) principles, Krames et al. analyzed recent literature to reprioritize pain treatments for FBSS to reflect a more up-to-date and fiscally responsible continuum of care. They ultimately concluded that that SCS should be considered ahead of long-term systemic opioid therapy or repeat spinal surgery in the management of FBSS.
How Are the Best Outcomes Achieved?
When the senior author started her neuromodulation practice, there were many spine surgeons in her region who were not supportive of SCS. The referrals were thus limited to patients for whom SCS was considered as a last resort. Patients had been living in pain for 10 to 15 years and were on a significant number of medications. Psychosocial overlay was extreme. Thus not surprisingly, outcomes in this patient population were subpar. Over time, with adoption of SCS therapy as a means for managing patients with FBSS, referrals occurred earlier and outcomes improved dramatically. Thus if the perception in one’s practice is that SCS does not work and should be only attempted as a “hail Mary” in the most challenging patients, it is unlikely to be successful.
Patients should be considered for SCS if they have chronic neuropathic pain for more than 3 to 6 months following spine surgery despite conservative therapy. Longer durations of chronic pain prior to SCS have documented poorer outcomes. Before SCS, all candidates undergo psychological screening. Although this is mandated for SCS surgery, we recommend that all surgeons operating for pain consider incorporating a pain psychology evaluation into their practice. Substance abuse or feelings of demoralization or depression are correlated with worse outcomes and patients without psychiatric disorders have greater rates of improvement in pain and function. Additionally, thoracic magnetic resonance imaging (MRI) is obtained to rule out any pathology that would preclude lead placement. Extensive discussions of the risks and benefits of the procedure, about the need for an SCS trial to assess potential responses, and about what is considered a good outcome for pain relief (>50%), are important preoperative steps prior to undergoing permanent SCS.
All patients undergo an SCS trial to assess if the placement of a permanent stimulator will reduce pain by greater than 50% or improve function in activities of daily living by 50%. Percutaneous leads are placed into the epidural space and attached to an external programmable pulse generator. The trial is performed on an outpatient basis for 7 to 10 days. In addition to determining if SCS will be effective for the patient, the trial also provides information about the optimal location of electrodes to obtain maximal pain reduction. Energy consumption analysis and the patient’s ability to use the device may be used to guide selection of the optimal battery for the device. A pain management specialist is involved in this trial process and serves as a conduit between FBSS patients and spine surgeons for SCS. These physicians play an important role in building an SCS practice. Further, developing these relationships with pain practices and providing a service many other spine surgeons do not provide is a means to expand the spine surgeon’s practice. Additionally, this conduit of patients will further bring traditional spine surgery patients into the surgeon’s practice.
The Surgical Procedure
Most commonly, spine surgeons implant paddle leads ( Fig. 25.1 ). To do this, a laminectomy or laminotomy is usually performed, one interspace below the “sweet spot,” as determined by the trial. The sweet spot identifies the electrodes that serve as active contacts during the trial for pain relief. Thus if the sweet spot is mid-T8 body, a T9–T10 laminectomy is performed. These leads are firm and rectangular, and can have between 4 and 32 contacts, with the majority having 16 contacts. This paddle is quite different from those introduced in the 1990s, which had four contacts with spaces between the contacts that precluded bipolar stimulation.
