Interventions in Chronic Pain Management. 6. Interventional Approaches to Chronic Pain Management

6.1 Clinical Activity: To design an interventional spine protocol for diagnosis and treatment of recalcitrant buttock and hip pain in a 25-year-old patient 

SEVERE BUTTOCK PAIN with or without limb radiation is a common malady, with an extensive differential that may be difficult to diagnose, let alone cure. Therapeutic and diagnostic intervention practices can be used when more conservative treatments fail. The following discussion reviews several spine interventional treatments commonly used to treat and diagnose patients with hip and buttock pain.

The sacroiliac joint is a diarthrodial joint that is capable of referring pain to the buttocks, groin, or lower extremity. It has been found to be the pain generator in 13% to 30% of patients with chronic low back pain, when the diagnosis was confirmed with controlled fluoroscopically guided techniques.1 The innervation of the sacroiliac joint remains controversial; it is believed that the joint receives both dorsal and ventral innervation from the spinal nerves of L4 through S1, from the ventral rami, or from the lateral branches of the posterior rami of L4 through S3. Diagnostic injections are the standard for identifying the sacroiliac joint as the pain generator. Interventional options in the treatment of patients with sacroiliitis or sacroiliac joint dysfunctions include sacroiliac joint injections and/or neuroablative lesioning. Therapeutic sacroiliac joint injections are proven clinically effective in the treatment of sacroiliac joint pain.2, 3, 4 This form of injection should be performed by using fluoroscopy, computed tomography scan, or ultrasound to ensure intra-articular flow. Clinical sacroiliac injections without imaging have been shown to be intra-articular in only 22% of subjects.5 A patient should have no more than 6 injections per year.

Patients who report greater than 50% improvement in their pain after at least 2 injections into the sacroiliac joint should be considered for neuroablative lesioning.6 Radiofrequency ablation of the sacroiliac joint is a commonly used neuroablative technique. It can be performed 2 different ways: with a monopolar setup or a bipolar setup. Monopolar radiofrequency ablation is performed with a single active electrode, a grounding pad, and a radiofrequency lesion generator. A lesion is generated at 80°C around the active electrode, which is placed near the medial branch nerve. Bipolar radiofrequency ablation is performed with 2 electrodes (1 active, 1 passive) and a radiofrequency lesion generator. The 2 electrodes are placed in the sacroiliac joint less than 6mm apart.7 The lesion is generated from the active electrode to the passive electrode at 80° to 90°C. Approximately 15 lesions are delivered to the sacroiliac joint when using the bipolar technique.

Piriformis syndrome is a clinical condition that primarily causes buttock pain and may be accompanied by “hip pain” or radiating leg pain.8 The symptoms may resemble pain generated from the sacroiliac joint, lumbar nerve root, or hip. The treatment of piriformis syndrome includes physical therapy, manipulation, injections, or surgery. Successful injections into the piriformis muscle were reported with the use of electromyography,9 fluoroscopy,10 computed tomography scan,11 magnetic resonance imaging,12 and ultrasound.8 Benzon et al13 used a combination of fluoroscopic guidance and electric stimulation to optimize needle placement; the needle was placed 1.5±0.8cm lateral and 1.2±0.6cm caudal to the lower border of the sacroiliac joint at a depth of 9.2±1.5cm to stimulate the sciatic nerve.13 Botulinum toxin types A and B have been injected into the piriformis with good success.14, 15

Although hip pathology does not classically present as buttock pain, the hip joint must be considered as a possible pain generator if hip motion is limited or buttock pain results from rotation of the hip. Diagnostic hip injections with bupivacaine (Marcaine) or lidocaine under fluoroscopic or ultrasound guidance may be useful. The value of corticosteroid injections into the hip joint is uncertain. The injections may lead to worsening osteonecrosis of the femoral head16 and have not been shown to reduce the need for total hip arthroplasty.17 There also may be an increased incidence of infection rate if steroid is injected into the hip within 1 year of total hip arthroplasty.18 There may be a role for viscosupplementation for short-term pain relief in some patients with osteoarthritis.19

Lumbar facet joints, also known as zygapophyseal joints, are diarthrodial articulations between the posterior elements of adjacent vertebrae.20, 21 The lumbar zygapophyseal joints are innervated by the medial branch of the dorsal rami of the spinal nerves. Each medial branch nerve supplies at least 2 facet joints.22 The prevalence of zygapophyseal joint−mediated pain in patients with chronic spinal pain is 15% to 45% with controlled diagnostic blocks.22 Patients diagnosed with lumbar facet−mediated pain may benefit from intra-articular injections, medial branch blocks, or neuroablative procedures. Intra-articular injections were reported to be effective with the injection of corticosteroids, local anesthetics, or normal saline.23 Medial branch blocks are commonly performed as diagnostic blocks, but these injections are reported also to have a therapeutic effect when performed with local anesthetics with or without steroids.24

The mechanisms of pain relief from epidural steroid injections remain poorly understood. Corticosteroids are believed to reduce pain by acting as potent anti-inflammatory agents in 3 ways: (1) reducing the effects and production of inflammatory mediators,25 (2) suppressing ectopic neuronal discharges by stabilizing the neural membrane,26 and (3) reducing C-fiber conduction.27

The interventional pain physician must consider the patient’s symptoms, physical examination, comorbidities, prior responses to treatments, radiographic studies, anatomic deviations or prior surgeries, medication, and potential risks and complications of a given procedure. These factors will help the injectionist to choose the best medication, dosage, and injection for the specific problem.

Interventional physicians may access the epidural space from the caudal, interlaminar, or transforaminal route. It is recommended that caudal and interlaminar injections be performed with fluoroscopic guidance to ensure accuracy of placement into the epidural space28, 29; transforaminal injections must be done under fluoroscopy. Caudal epidurals are performed by the placement of a needle through the sacrococcygeal ligament that covers the sacral hiatus into the epidural space. The advantages of caudal epidurals are a minimal risk of inadvertent dural puncture and the ease of entry into the epidural space. Disadvantages include the substantial volume of fluid required to reach the pain generator, lack of selectivity, and potential for placing the needle outside the epidural space.30 Interlaminar steroid injections are performed by placing an epidural needle, such as a Tuohy needle, through the ligamentum flavum into the posterior epidural space. The disadvantages of the interlaminar injections are the risk of subarachnoid puncture with consequent spinal block or headache, intravascular placement, deviation of the needle to the nondependent side, difficult placement in postsurgical patients, and potential for placing the needle outside the epidural space.31 Transforaminal epidural steroid injections are performed by guiding a spinal needle into the superior intervertebral foramen just inferior to the pedicle. By taking the transforaminal approach, a higher concentration of medication is placed closer to the targeted nerve root. Disadvantages of transforaminal injections include the potential for intravascular or intraneural injections, neural trauma, or technical difficulty in the presence of fusion and/or hardware.31

Patients with lumbar epidural fibrosis often have pain that is resistant to conservative care and epidural steroid injections. The decreased success rate may be explained by adhesions preventing the medication from reaching the site of pathology, intraneural vascular congestion caused by the circumferential squeezing effect of perineural fibrosis, and/or mechanical tethering of the nerve root to the spinal canal with subsequent neuropraxia during ambulation.

Percutaneous epidural neuroplasty is an interventional technique that allows the interventional physician to lyse epidural adhesions with a semirigid catheter before administering medication. The catheter is inserted into the epidural space from a caudal, transforaminal, or interlaminar approach. A nonionic contrast agent (eg, iohexol) is injected into the epidural space to identify adhesions under fluoroscopy. (This procedure can also be performed via epiduroscopy.) The catheter is then advanced into the scar tissue with the bevel of the needle in a ventrolateral position to facilitate passage and decrease the chances of shearing the catheter. After the obstruction from the adhesion is mechanically lysed, contrast can be injected to confirm lysis. The contrast medium fills the defect that was caused by the adhesion. With the adhesion lysed, medications can now be administered. Chemical neurolysis with hypertonic saline and/or hyaluronidase injected via the catheter may increase the effectiveness of the procedure.32, 33

6.2 Clinical Activity: To review the treatment options for implantable devices in the treatment of a 50-year-old man who has severe chronic back pain unresponsive to nonsurgical treatments 

In the appropriate patient, implantable devices are an excellent means of treating pain. Implantation therapy should be reserved for patients who do not achieve adequate benefit or who have intolerable side effects with less invasive treatments. Implantable therapies should not be viewed as a cure for chronic pain but as a therapeutic option that can significantly reduce pain while improving function and quality of life.

In spinal cord stimulation (SCS), electronic impulses are delivered to the dorsal columns of the spinal cord by means of an implanted stimulator and electronic lead system. The leads are strategically placed to treat a specific pain complaint. Neurostimulation can also be delivered to peripheral nerves by stimulating a specific branch of an affected limb. The spinal cord is more commonly stimulated than individual peripheral nerves because pain generally involves multiple nerves. The use of electricity for pain relief is based on the gate-control theory, which suggests that a metaphoric “gate” exists in the spinal cord that prohibits the transmission of pain signals to the brain by stimulating the dorsal columns. Other theories underlying the use of neurostimulation include antidromic peripheral nerve stimulation, conductance blockade of the spinothalamic tract, activation of inhibitory pathways, blockade of sympathetic outflow, and activation or release of inhibitory neuromodulators.34

The stimulator lead should be placed in a position to optimize “capture” of pain responses. Various arrays of lead configurations, sometimes involving multiple leads, can be used to optimize pain coverage. Typically, a trial is performed before implantation, and the lead is left in place for a few days so that the patient can assess whether there is benefit in terms of pain control and function. The trial allows the patient and physician to determine if SCS is effective for the type, location, and severity of pain and to evaluate the effectiveness of various SCS parameters. The patient should experience a paresthesia instead of a pain in the targeted area.

SCS is shown to significantly improve quality of life, pain intensity, and mood.35 In patients with persistent radicular pain after lumbar surgery, SCS is more effective than reoperation in terms of pain relief, patient satisfaction, and use of health care resources. In many patients with prior lumbar spine surgery, SCS obviates the need for further surgery, and there is lesser morbidity with greater reversibility.36 SCS tends to be less effective for the control of axial pain than peripheral pain complaints. Similarly, SCS has been found to be an excellent treatment for neuropathic pain disorders and is generally ineffective for nociceptive pain. New technology and placement of electrode arrays may allow for better treatment of axial spinal pain. A systematic review of the literature on SCS noted a significant improvement in functional capacity, excellent satisfaction with spinal cord stimulation, and a significant increase in the proportion of patients who work after SCS compared with work experience before SCS. Analgesic use is often reduced after successful SCS implantation.37

SCS has a relatively low risk of complications. Risks of a trial include infection, bleeding complications, insufficient pain relief, dural puncture headache, and increased pain. After implantation, there may be a loss of effective stimulation. This change may be from equipment failure, such as lead fracture, movement of leads or increased stimulation requirements related to adhesions, change in pain distribution, or change in pain character.36 An implanted SCS system precludes the patient from having magnetic resonance imaging. Defibrillators and electronic pacemakers can adversely affect SCS systems (and vice versa) and may prevent consideration of SCS.

In patients who have received only limited benefit from oral medication treatment, medication delivery via an indwelling epidural catheter may prove more effective. Pumps can also improve pain control in patients who benefit from but have trouble regulating their oral medications. A trial should precede permanent implantation to assess benefit and side effects from the medications. Trials can be performed by using a variety of methods, including a single bolus of intrathecal or epidural medication or continuous infusion. Intrathecal pumps can be used to deliver various medications directly into the thecal space. The pump can be filled with various medications including opioids, clonidine, baclofen, bupivacaine, and ziconotide.38 With intrathecal pumps, the medications are delivered to the intrathecal space at much lower concentrations than necessary for systemic absorption, and side effects are generally lower. Drowsiness, nausea, pruritus, and other intolerable side effects are often improved with an intrathecal delivery system.

Patients with pumps implanted for intrathecal pain have reported significant improvement in activities of daily living, ambulation, quality of life, sleep, satisfaction with therapy, and reduction of sensorimotor disturbances and oral analgesic use. Intrathecal pain pumps can be efficacious for both neuropathic and nociceptive pain conditions with nonopioid medications such as clonidine and bupivacaine used as adjunctive medications for neuropathic pain.39 Combinations of medication tend to be more effective than opioids alone because a synergy seems to exist between opioid and nonopioid medications that use different mechanisms at different pain receptors. This synergy from a polypharmacy approach can be used to reduce opioid requirements, perhaps reducing both side effects and opioid tolerance.40

Intrathecal medication delivery has its drawbacks. Implanting a pump is not an innocuous procedure. The pump is a mechanical device that is prone to problems. These issues include catheter kinking, mechanical failure, catheter tip granulomas, and infection. Complications from medication infusion can result in significant neurologic, urologic, and respiratory symptoms such as paralysis, confusion, urinary retention, respiratory compromise, and death. Less significant side effects from infusions, including pruritis, decreased libido, peripheral edema, nausea, vomiting, and constipation, are more common.39 The patient is dependent on frequent refills of medications and proper adjustment of the pump parameters. Tolerance may develop, and repeated adjustment of medication may be necessary. Errors in medications can cause withdrawal or overdose symptoms.

Patients should be selected carefully for any implantable device. It is wise to obtain a psychologic evaluation before a trial for an implantable device. Caution is advised in patients with drug-seeking behavior, significant psychiatric disease, excessive pain behavior, and major secondary gain issues. Patients must have the cognitive aptitude to assess risks and benefits. They must also be able to communicate satisfaction with the pain control and the functional improvement gained from the trial undertaken before device implantation. The patient who is to receive an intrathecal pain pump should be deemed reliable to return for scheduled appointments because failure to do so can result in withdrawal symptoms. Before the trial and implantation, a thorough discussion with the patient should have taken place, with all questions answered to the patient’s and the physician’s satisfaction. The patient should be given realistic expectations for success to avoid disappointment and deterioration of the physician-patient relationship. Before scheduling the implant procedure, it is prudent to guide the patient to available resources such as websites, videos, and literature that detail the procedure.41