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19 Articles in Volume 19, Issue #6
Arthrofibrosis: Targeting Hormones after Childbirth to Relieve Frozen Shoulder, Inflamed Joints
Can CGRP Help Clarify Why Migraine Is More Common in Women?
Case Report: Managing Chronic Pelvic Pain in Men
CGRP Monoclonal Antibodies for Chronic Migraine: Year 1 of Clinical Use
Chronic Pelvic Pain as a Form of Complex Regional Pain Syndrome
Correspondence: Continuing the “Pain Specialist” Dialogue
Endometriosis and its Misunderstood Etiology
Evolving Management Strategies for Osteoarthritic Pain
Gamma PEMF Therapy: A Pilot Study For Its Use in Managing Opioid Addiction
Guest Editorial: Sex Differences in Pain
How to Provide Effective Pain Management to LGBTQ Individuals
Interscalene Peripheral Nerve Stimulation for Post-Operative Chronic Shoulder Pain
New ICD-11 Codes Set to Improve Pain Care in the Primary Setting
Perspective: Could NGF Antagonists Be the Safest, Most Efficacious Class of Drug We Have to Treat Pain?
Rheumatoid Arthritis and Cognition: Is There a Genetic Link?
Targeting Nerves Provides Alternative to Opioids for Joint Arthroplasty
The Sex Question in Primary and Pain Care
What is capsaicin’s role in treating osteoarthritis?
When Pain Clinicians Have to Be the Villain: Communication Strategies to Bridge the Divide

Interscalene Peripheral Nerve Stimulation for Post-Operative Chronic Shoulder Pain

As an alternate analgesic therapy, PNS may have potential as an integral part of the pain practitioner’s toolkit.
Pages 64-68

Shoulder pain is commonly a chief complaint among patients seen in chronic pain clinics, a pain which may be severe to the point of debilitation. The wide range of motion (ROM) of the shoulder may be reduced, restricting quality of life. Numerous modalities may be used to treat shoulder pain with variable success rates, including medications, physical therapy, steroid injections, nerve blocks, and neuromodulation.

Here, the authors report on a retrospective case of a 54-year-old man presenting with refractory chronic right shoulder pain associated with allodynia and hyperalgesia. The patient attempted conservative management, both pharmacological and interventional, with no significant reduction of symptoms. A right interscalene peripheral nerve stimulator was placed to target the axillary nerve, which was the possible source of his refractory pain. During an active 8-week trial, the patient reported significant relief of pain, allodynia, and hyperalgesia and placement of a permanent stimulator was pursued.

The Patient

A 54-year-old male presented with refractory chronic right shoulder pain for the past six years post-repair of a grade III acromioclavicular joint separation. Physical examination revealed positive right acromioclavicular joint and anterior deltoid allodynia and hyperalgesia. The patient’s right shoulder had full ROM with no motor weakness.

The patient initially attempted conservative management with prescribed opioids, neuropathic agents, muscle relaxants, NSAIDs, and physical therapy with no significant improvement. He attempted interventional pain procedures, including stellate ganglion blocks, trigger point injections, cervical epidural steroid injections, cervical spinal cord stimulator placement, and radiofrequency ablation of the right suprascapular nerve. With each intervention, he had relief for less than a week or no significant reduction of the allodynia.

Peripheral nerve stimulation (PNS) of the right axillary nerve was attempted, which resulted in a 40% reduction in pain but no change in allodynia and hyperalgesia. The suspected source of allodynia and hyperalgesia at the right anterior aspect of the shoulder was the C5 nerve root. To better target this, the percutaneous electrical lead was removed, and a new lead was placed at the right interscalene groove between the anterior and middle scalene muscles at the level of the cricoid cartilage in the neck under ultrasound guidance. This approach better engaged the nerve roots of the brachial plexus compared to the previously targeted axillary nerve. The position of the new lead was confirmed by verifying the generation of paresthesia overlapping the distribution of the patient’s typical region of pain using electrical stimulation.

Two weeks after placement, the patient reported 80% improvement in pain with minimal change in allodynia and hyperalgesia. The patient stated that this was the most profound pain relief in terms of duration and intensity that he had been able to achieve with an interventional pain procedure. During a 1-month follow-up appointment, the patient reported that his overall reduction of pain was 50%, and that his allodynia and hyperalgesia over the right supraclavicular and anterior deltoid region decreased. He noted that when the stimulator was turned off, the pain, allodynia, and hyperalgesia returned to its original intensity within 30 minutes.

At a 2-month follow-up appointment, the overall reduction of pain had remained the same, and the patient was able to tolerate wearing clothing (as compared to baseline). During this visit, the peripheral nerve stimulator was removed, as he had reached the maximum 60 days of therapy. At the conclusion of therapy, he voiced an almost immediate return of hyperalgesia and associated myofascial tightness over the right supraclavicular and anterior deltoid region. The next course of treatment discussed was to pursue permanent implantation with an alternative stimulator at the interscalene site.

Consequently, shoulder dislocations may present with axillary nerve dysfunction, muscle weakness, muscle spasm and/or significant pain. (Image: 123RF)

Discussion

The shoulder accounts for almost half of all major joint dislocations among individuals in the US,1 where the axillary nerve is frequently injured.2 Consequently, shoulder dislocations may present with axillary nerve dysfunction, muscle weakness, muscle spasm and/or significant pain. Tissue damage and axillary nerve injury may also occur; though rare, it is more common in the elderly.2

Through a combination of peripheral and central sensitization, acute pain following nerve injury may become chronic, potentially leading to allodynia and hyperalgesia.3 Collectively, these observations highlight both the association of shoulder dislocation with neuropathic pain, and the prevalent need for effective pain management following shoulder dislocation and subsequent reduction, especially with increased rates in population aging.4 The following section briefly discusses treatment options for post-operative pain.

Traditional Treatment Options

Several options for post-operative analgesia exist, including opioids, NSAIDs, celecoxib, gabapentin, pregabalin, ketamine, clonidine, and benzodiazepines. Each pharmacological agent may be effective but also carries risks:

  • Systemic opioids may lead to side effects such as nausea, vomiting, constipation, and addiction.5 Additionally, opioids have been associated with respiratory depression, hypoventilation, hypoxia, and development of sleep-disordered breathing (about one-quarter of patients taking chronic opioids have central sleep apnea).6
  • Over-the-counter NSAIDs have been associated with GI bleeding, ulceration, cardiovascular events, impaired bone healing, and renal impairment.7
  • Selective COX-2 inhibitors, such as celecoxib, have similarly been associated with impaired wound healing and increased cardiovascular events and are thus contraindicated in certain high-risk patients.7
  • Gabapentinoids, including gabapentin and pregabalin, have been associated with dizziness and sedation. Evidence of the effectiveness of gabapentinoids for post-operational pain in children is sparse.8
  • Ketamine use has been associated with increased risk of nightmares, hallucinations, long-standing memory impairment, and addiction.9
  • Clonidine, as an addition to local anesthetics to increase the duration of nerve blocks, has been associated with increased risk for bradycardia, fainting, and orthostatic and arterial hypotension.10 Its use is also limited to inpatient settings.11
  • Benzodiazepines, such as diazepam, have muscle relaxant properties that may be helpful in treating spasmodic pain. However, these medications have significant withdrawal symptoms if not tapered properly, especially in the elderly.8

Traditional options for the management of post-operative pain are more thoroughly discussed in recent guidelines approved by the American Society of Regional Anesthesia and Pain Medicine (ASRA).8

Peripheral Nerve Stimulation as an Alternate Analgesic

PNS may offer an additional treatment strategy to treat allodynia and hyperalgesia, as the method is often used to guide interscalene blocks for a variety of upper extremity surgeries. Such stimulation may also be useful for determining catheter placement prior to injection of a long-acting anesthetic for prolonged analgesia post-op (ropivacaine administration; see Figures 1 and 2).

Figure 1. Right interscalene PNS lead placement via needle.

Figure 2. Post-operative PNS site with external device adaptor.

Peripheral nerve stimulators have been shown to provide sustained pain relief with local intramuscular placement. In general, about 25% of patients receiving pain medications experience adverse effects,12 but with intramuscular PNS, only minimal and relatively rare side effects have been reported, including fragmentation of the electrical lead and infection.

While the exact mechanism for intramuscular PNS analgesic effects has not been determined, several theories have been postulated. Melzack and Wall’s gate control theory13 describes how electrical activation of large diameter myelinated afferent nerve fibers may block pain signal conduction to the spinal cord from small diameter pain fibers. Therefore, pain transmission may be inhibited by PNS because the “gate” (spinal cord) only permits limited signal transfer.14

This reaction is distinct from the proposed mechanism of transcutaneous electrical nerve stimulation (TENS), where central excitability is reduced by activating endogenous inhibitory pathways (opioid receptors) to block pain transmission with electrical contacts on the skin, thereby causing a sensation of paresthesia.8 The use of TENS for analgesia is limited by patient tolerance of uncomfortable high-intensity electrical current on the skin.

Since no pain management method is perfect, the addition of PNS as an analgesic clinical tool offers an exciting opportunity. Fewer than half of surgical patients report adequate post-operative analgesia,12 and in this case, the patient’s pain was refractory to opioids, NSAIDS, steroids, cervical spinal cord stimulator placement, and radiofrequency ablation of the right suprascapular nerve.

What the Literature Says About PNS

Regardless of the mechanism, intermittent sessions with PNS over a period of weeks has been shown to provide sustained relief for a variety of problems, including chronic low back pain,15,16 post-op knee pain,17 phantom limb pain,18 hemiplegic shoulder pain,19 and subacromial impingement syndrome.20 The axillary nerve branches off of the brachial plexus in the posterior cord, formed by C5, C6 fibers. Recognizing that the axillary nerve was most likely affected by the acromioclavicular dislocation and was therefore responsible for symptoms, the authors anticipated that targeting the C5, C6 origin by interscalene block with a peripheral nerve stimulator could provide sustained post-operative analgesia for the patient.

Typically, patient response to treatment is assessed as “positive” if the pain is reduced beyond a particular threshold, although the threshold and the pain scale used may vary between studies. Fortunately, a large percentage of patients respond positively to PNS in a variety of clinical scenarios.

In the authors’ review of the literature, response rates varied and may be related to the nature of the pain or the cause of injury. In one report, 14 out of 16 limb amputee patients responded to stimulation positively (≥ 30% pain reduction);18 five out of five hemiplegic shoulder pain patients responded to stimulation positively (≥ 50% pain reduction);21 six out of nine chronic back pain patients experienced ≥ 50% pain reduction;15 and five out of five post-operative knee arthroplasty patients reported ≥ 67% pain reduction (four reported complete pain amelioration during active stimulation).17 While the scales and thresholds reported in the literature are variable, a consistent finding is improvement in a significant amount of patients’ pain with intramuscular PNS.

Intramuscular PNS offers pain relief during active stimulation periods with extensive coverage of the area of pain in patients who respond. For treatment of phantom and/or residual limb pain, responders reported an average paresthesia coverage of 95% of the painful area when leads were placed near the femoral and/or sciatic nerves.18 During the active stimulation period, the patient reviewed in this case report had as high as an 80% coverage of paresthesia when the lead was placed near the brachial plexus nerve roots between the anterior and middle scalene muscles.

Analgesic intramuscular PNS also provides an extended period of pain relief after initial treatment. Hemiplegic shoulder pain patients, who received PNS in the trapezius muscle 6 hours per day for 3 weeks, reported an average reduction of 70% in the Brief Pain Inventory (BPI)-3 pain score, and an average reduction of 61% in BPI-3 from baseline 4 weeks after the stimulation treatment ceased.22

Similarly, five hemiplegic shoulder patients with implanted PNS for 3 weeks, who received 6 hours active stimulation per day, reported ≥ 50% pain reduction from baseline at 6 and 12 months, with four of the participants also reporting ≥ 50% pain reduction from baseline at 24 months.21 Stroke survivors with chronic shoulder pain and subluxation, who received 6 hours intramuscular stimulation per day for 6 weeks via a total of 4 leads (targeting the supraspinatus, posterior deltoid, middle deltoid, and trapezius), reported “no pain” in 34% of cases six months after treatment compared to 10% of patients who had been placed in a cuff-type sling for six weeks.23 Improved shoulder abduction ROM was noted in patients with chronic pain associated with subacromial impingement syndrome who received intramuscular PNS targeting the axillary nerve in the middle and posterior deltoids. They also maintained pain reduction for at least 12 weeks after the end of stimulation.20

If pain returns, analgesia may be re-initiated upon a new period of stimulation. This approach was demonstrated recently in a patient with shoulder pain who, with a single lead implanted near the terminal branches of the axillary nerve to the deltoid, became pain-free after 3 weeks of stimulation but was forced to cease therapy because of an acute illness and returned to baseline shoulder pain scores (BPI-3). After the illness resolved, the patient was able to undergo continued stimulation again, and returned to pain-free status for several months thereafter.24 The attractive on-off flexibility intramuscular PNS offers is different from many pharmacologic therapies which may have undesirable withdrawal effects and extensive half-lives.

Clinical Considerations

Important clinical considerations for intramuscular PNS include the time since injury and duration of stimulation. Each of these may impact patient outcomes. For example, intramuscular PNS given to patients with shoulder pain post-stroke tended to respond (maintaining a 2-point reduction in BPI-12 score) at higher rates (94%) if treated within 77 weeks of stroke onset compared to patients treated after 77 weeks since stroke (7%).19 Extending the stimulation period may increase the persistence of an analgesic effect.

Patients with residual limb pain who received 4 weeks of placebo followed by 4 weeks of continuous PNS reported, on average, a return to baseline scores in BPI-5 four months after treatment ended. In contrast, patients who received 8 weeks of continuous stimulation reported reduced BPI-5 at 4 months, as well as an 86% reduction even up to 10 months after treatment ended.15

It would seem that ideal treatment of intramuscular PNS should take place early and with a sufficiently long period of stimulation. In the presented case, the patient had multiple interventions prior to the intramuscular PNS trial performed approximately 6 years after onset of pain (close to 77 weeks). The patient also underwent an 8-week trial with minimal improvement after removal of the stimulator.

Potential Complications

One of the primary concerns with prolonged intramuscular PNS analgesia is the possibility of lead fragmentation, particularly during removal. Fragmentation may lead to complications of granulomas.20 It may also lead to fragment migration and/or infection risk, but based on post-stroke shoulder pain studies accounting for a total of over 850 implanted electrodes, it is estimated that the probability of lead fracture during removal with either of these subsequent medical complications is 0.06% per implanted electrode.23

In the presented case, the electrical lead was removed intact with no complications after treatment. If suspected, the presence of lead fragment retention in vivo may be assessed radiographically.25 Although electrodes are typically biocompatible, they can be removed in a minor outpatient procedure.23 Encouragingly, the safety of magnetic resonance imaging (MRI) for patients with retained PNS lead fragments has been demonstrated up to 1.5 Tesla, with only minor magnetic field interactions and associated heating.26

An inherent risk in any in vivo foreign body introduction is infection. This is particularly true of the electrical leads used in intramuscular PNS since they traverse the skin, potentially translating small distances in and out of the body as the patient moves, creating an increased opportunity for bacterial entry. Newer designs incorporating coils have been shown to have lower risks of infection.27

Which Patients May Be Eligible for PNS?

The number of patients who may actually benefit from analgesic intramuscular PNS may be limited. In prior studies, exclusion criteria included the presence of implanted pacemakers, ongoing infections, bleeding disorders, chronic pain disorders, diabetes, recent injections, pregnancy, and allergy to metals. Some of these enrollment restrictions were to limit confounding factors, but others were because of safety risks. Therefore, many patients may not be eligible for intramuscular PNS therapy, and the response rate and efficacy in patients who would have been excluded may be dissimilar to reported results. Further, insurance coverage may be limited or even non-existent for patients who would be good candidates for intramuscular PNS therapy. Regardless of strong data supporting their use, many innovative pain management therapies are regarded by insurance companies as experimental, perhaps because of short-term cost savings.

Conclusion

While case studies in the literature to date have had limited generalizability, this retrospective report adds another piece of support that, broadly, peripheral nerve stimulation may be a useful analgesic technique for chronic pain. More specifically, this study shows that PNS in the interscalene groove may safely provide neuropathic shoulder pain patients sustained pain relief. Future studies with appropriate controls and significant sample sizes will help to definitively assess the indications for and appropriateness of interscalene PNS compared to other therapies. In addition to post-operative pain management, the use of PNS may prove to be of significant benefit in patients with chronic pain resistant to traditional pharmacological therapy, and large-scale studies should be explored with regards to this population.

To the authors’ knowledge, this is the first report demonstrating the efficacy of peripheral nerve stimulator placement at the interscalene site for analgesia post-acromioclavicular dislocation repair. The addition of peripheral nerve stimulator placement to the clinician’s post-operative pain management toolbox may be useful as an adjunct therapy in a multimodal analgesic regimen, or even as a standalone approach after other methods have been exhausted.

Last updated on: October 7, 2019
Continue Reading:
Agonism and Antagonism of the Muscles of the Shoulder Joint: An SEMG Approach
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