Peripheral nerve stimulation of the sacroiliac joint

Introduction

Peripheral nerve stimulation (PNS) is being explored for a variety of clinical indications, including plexus injuries, focal mononeuropathy, postamputation pain, back pain, sacroiliac joint pain (SIJ), headache, facial pain, and arm and limb pain. PNS is an attractive treatment option for patients with SIJ pain who have failed more conservative treatments but who are not interested in a more invasive procedure because PNS is reversible, minimally invasive, and inherently less morbid than sacroiliac fusion. This chapter focuses on treatment of patients with SIJ pain with PNS.

Pain and SIJ dysfunction is primarily caused by either a traumatic event through the disruption of normal anatomy or may develop over time through the degeneration of the structure listed below ( Table 6.1 ).

TABLE 6.1

Frequent Causes of Sacroiliac Joint Pain

Trauma or Joint Disruption	Degeneration
Car accident	Osteoarthritis
Fall on buttock	Infection
Crush injury	Previous lumbar spine surgery
Childbirth	Joint replacement surgery

Sacroiliac joint pain often presents with pain below the belt line with radiations into the groin and lower extremity, infrequently with radiations below the knee in the L5 to S1 dermatomal pattern ( Figs. 6.1 and 6.2 ).

Characteristics of SIJ pain include

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Aching in quality
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Absence of burning quality
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Numbness and tingling
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Radiating down the posterior thigh to the posterior knee joint, glutes, sacrum, iliac crest, and sciatic distribution
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Worsening with static standing, bending forward, donning shoes or socks, crossing the leg, rising from a chair, or rolling in bed
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Relief with continuous change in position
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Typically, an absence of thigh pain, especially in older patients

Pain relief from PNS as sensed through paresthesia is mediated by A-beta fibers; however, the mechanism of segmental pain relief may share similar pathways with the spinal cord stimulation because the same A-beta fibers traverse the dorsal columns. It has been hypothesized that the PNS may affect local concentrations of biochemical mediators that enhance the pain response. Biochemical mediators of pain such as neurotransmitters and endorphins lead to increased local blood flow that may contribute to the development of chronic pain. Studies have suggested that the PNS may directly inhibit pain neurotransmission, possibly through alteration of local inflammatory mediators, as demonstrated by studies in healthy human volunteers, whereby elevated pain thresholds were observed during direct PNS. In peripheral nerve injury, ectopic discharges are transmitted by injured nerves, specifically low-threshold A-beta and high-threshold A-delta and C fibers, all of which may contribute to the generation of pain. It is postulated that PNS or direct nonpainful electrical stimulation may alter ectopic discharge, leading to decreased pain perception. Recent studies, however, have proposed that intact nerve fibers adjacent to the peripheral site of injury may be the culprits for pain generation via Wallerian degeneration.

Indications

Peripheral nerve stimulation is indicated for pain management in adults who have severe intractable chronic pain of peripheral nerve origin, as the sole mitigating agent, or as an adjunct to other modes of therapy used in a multidisciplinary approach.

Contraindications

Peripheral nerve stimulation is contraindicated in patients who are poor surgical candidates; pregnant; unable to understand or operate the system; will be exposed to shortwave, microwave, or ultrasound diathermy; have occupational exposure to high levels of nonionizing radiation; or have implanted cardiac systems.

Perioperative considerations

Patient selection

Peripheral nerve stimulation is an appropriate treatment option for patients who maintain intractable pain even after conservative treatments such as SIJ injections or radiofrequency ablation of the SIJ.

Peripheral nerve stimulation can also be used earlier in the treatment paradigm when a patient does not want to have a more aggressive treatment such as fusion of the SIJ.