Musculoskeletal Injections

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Chapter 22 Musculoskeletal Injections

Iliopsoas, Quadratus Lumborum, Piriformis, and Trigger Point Injections

Anne Marie McKenzie-Brown, Kiran Chekka, Honorio T. Benzon

Chapter Overview

Chapter Synopsis: Myofascial pain syndrome arises from the fascia tissue surrounding the muscles that interact with the skeletal support system of the back. The pain results in a trigger point, a localized taut band of muscle tissue that is tender to the touch and may cause radiating pain. The quadratus lumborum and iliopsoas muscles are typically affected by myofascial pain. Their deep location and intimate association with vascular and abdominal organs make injection at these muscles difficult, and identifying trigger points is quite subjective. Trigger points may be classified as active or latent. Similar to many chronic pain states, myofascial pain may begin with a nociceptive process from injury or strain and progress to a central sensitization that can lead to chronic pain. Trigger point injection is only one option for treatment; others include transcutaneous nerve stimulation, acupuncture, and physical therapies. Injected drugs are usually anesthetics or steroids with antiinflammatory effects. Fluoroscopic guidance can improve the success of trigger point injections.

Piriformis syndrome presents its own challenges, starting with proper diagnosis, which often comes by exclusion. This pain syndrome is marked by pain in the entire buttock that can radiate to back and leg areas. In about half of cases, the syndrome arises from trauma (including surgery), although not necessarily with direct or immediate consequences. Injections of the piriformis muscle with local anesthetic and corticosteroids can be used as therapy for pain. Fluoroscopic imaging or ultrasound is recommended for guidance of injections.

Important Points:

Trigger points in the quadratus lumborum and iliopsoas muscles are a common source of low back pain.

Quadratus lumborum and iliopsoas muscle injections are more accurately performed under fluoroscopic guidance because of their depth and location in the back.

When performing these injections, the practitioner should bear in mind that the quadratus lumborum and psoas muscles form the posterior abdominal wall and that there are associated organs and vascular structures anterior to these muscles.

Good results can be achieved with a thorough history and physical examination and careful patient selection often after other more common diagnoses are eliminated.

Using dual guidance with fluoroscopy and nerve stimulation allows the practitioner to safely and quickly predictably deposit medications into the belly of the piriformis muscle.

Practitioners should avoid injecting with any paresthesias or with a dye study that suggests intraneural, intravascular injection or injection into another structure.

Clinical Pearls:

Patients with quadratus lumborum pain have more pain arising from a supine to a sitting position than going from sitting to standing.

During the injection, the practitioner should look at the direction of the fibers when injecting the contrast to determine whether the injection has been in the quadratus muscle.

If the practitioner is unsure whether the injection is deep enough, he or she should stop and inject some contrast before advancing the needle.

Striated muscle has a characteristics appearance under fluoroscopy.

Clinical Pitfalls:

It is very important not to advance the needle too anteriorly with this injection because intraorgan injection is possible.

Large doses of local anesthetic can track into the epidural space and cause motor weakness, particularly with medial needle placement.

Epidural abscess has been anecdotally reported after trigger point injections.

Myofascial Pain and Trigger Point Injections

Myofascial pain is a common source of discomfort in the lower back. It is a painful condition that results in localized trigger points in the affected muscle. Myofascial pain syndrome was first clearly defined by Simons et al ¹ in the 1980s. It is characterized by trigger points in a specific muscle that may or may not respond to snapping palpation with a local twitch response and secondary decreased range of motion caused by the pain.¹ A trigger point is a localized taut band of muscle that is tender to palpation and produces pain that radiates when palpated. Tactile pressure to trigger points result in known, reproducible but nondermatomal referral patterns, also known as zones of reference.^1,² There is significant variability among practitioners in the identification of trigger points for the diagnosis of myofascial pain syndrome, although there is some evidence that the interrater reliability can be significantly improved with training.³ There is currently no gold standard test for trigger point identification, leaving a fair amount of subjectivity in the diagnosis. The twitch response is the most specific clinical test of a trigger point.¹ Trigger points are either active or latent.¹ Both active and latent trigger points have tender taut bands within the muscle, but latent trigger points are not associated with spontaneous pain. Latent trigger points may be the result of prior injury that then becomes painful with reinjury. Trigger points may be further subdivided into primary, secondary, and satellite trigger points.^1,² Primary trigger points become active as a result of trauma, overload or overuse injury, or after leaving a muscle in a prolonged contracted or shortened position.¹ Primary trigger points are in a discrete and separate location, with adjacent secondary trigger points that are often the result of spasm. Satellite trigger points are felt in the area of the referred pain remote from the primary trigger point location. The more irritable the trigger point, the more painful and extensive the referred pain; muscle size does not affect the amount or extent of the referred pain. Producing referred pain requires less pressure applied to an active than to a latent trigger point.¹ Latent trigger points, by definition, are inactivated when key trigger points are inactivated. ^1,² Although in the past their mere existence was questioned, we now know that trigger points can be documented by electromyography (EMG). Hubbard and Berkoff⁴ in their 1993 article were the first to report spontaneous needle EMG activity at the trigger point site now described as spontaneous electrical activity (SEA).⁴ Endplate noise that has been recorded from specific myofascial trigger points are thought to be attributable to excessive acetylcholine release in the neuromuscular junction.¹ Sympathetic activity appears to play a role in the activity of trigger points, with increased EMG amplitude seen under conditions of psychological stress and reduced firmness after a stellate ganglion block.^5,⁶

Myofascial pain is not the same as the pain endured by those with fibromyalgia, which is a more diffuse, centralized musculoskeletal condition with many associated symptoms (e.g., irritable bowel). Predisposing factors are anything that increases or changes the demands on the muscle. These may include repetitive use, deconditioning, poor posture, and occupational or recreational injury related to muscle imbalances.⁶ If treated early, the prognosis for myofascial pain is good. Treatment includes physical therapy, including stretching and strengthening or conditioning; trigger point injections; acupuncture; biofeedback; transcutaneous electrical nerve stimulation (TENS); and some medications. It is not entirely clear why trigger points are painful because there is no direct evidence of inflammation or enhanced nociceptors within the trigger point sites. However, after the pain is initiated, sensitization at the level of the dorsal horn may occur, which then progresses to the development of central sensitization and the subsequent development of chronic myofascial pain.⁶

Although local anesthetic is the substance most often used by pain physicians in trigger point injections, there is not much evidence for its superiority over normal saline or dry needling. It does appear that the best response to trigger point injections occurs if a local twitch response is elicited.⁷ Part of the problem is that placebo-controlled studies of local anesthetic injections are extremely difficult to accomplish. Many of the studies do not have consistent criteria for trigger points, and some do not distinguish between the tender points of fibromyalgia and the trigger points of myofascial pain. The relief from the local anesthetic consistently outlasts the half-life of the local anesthetic, giving some credence to central sensitization in myofascial pain syndrome. All local anesthetics are somewhat myotoxic, with bupivacaine being the most myotoxic by far, but the muscle quickly regenerates with little long-term ill effect.⁸ The mechanism of bupivacaine’s effect appears to be on the calcium release related to the channel-ryanodine receptor of skeletal muscle.⁸^–¹⁰ Injected steroid can also be myotoxic and should be used in low doses. Dry needling has been used with varied success but has the disadvantage of postneedling soreness, depending on the sensitivity of the patient before and during the procedure and whether or not acupuncture needles, associated with less soreness, were used.⁶ Although not all acupuncture points (e.g., in the ear) are the same as trigger points, there is a striking similarity between acupuncture points and those used for dry needling and for trigger point injections.

The muscles involved in myofascial pain of the lower back can be divided into the posterior (superficial to the transverse process) and anterior (deep to the transverse process) muscles. The posterior muscles include the multifidus (located closest to the spinous process) and the adjacent erector spinae muscles. The latissimus dorsi are attached to the spine by the thoracolumbar fascia, which envelops the multifidus and erector spinae muscles posterior to the quadratus lumborum. The thoracolumbar fascia extends distally and is in contact with the contralateral gluteus maximus and is thus thought an important factor in the transfer of load from the spine to the lower extremities. The quadratus lumborum is replaced distally by the iliolumbar ligament, one of the strongest ligaments in the body and the one responsible for much of the stability of the lumbosacral segment. More anteriorly and inferiorly to the quadratus are the iliopsoas muscles. These descend into the pelvic brim and attach to the lesser trochanter of the femur.¹¹

Pain involving the quadratus lumborum and iliopsoas muscles can be either primary myofascial or secondary in nature, reflecting pathology in the spine or other nearby organs. The quadratus lumborum, psoas major, and iliacus (which comes together to form the iliopsoas) muscles make up the major muscles of the posterior abdominal wall (Fig. 22-1).

Fig. 22-1 Lumbar region of back: cross section.

Quadratus Lumborum Injections

Establishing a Diagnosis

The diagnosis of myofascial pain is a clinical one, largely dependent on the findings of the history and physical examination. The quadratus lumborum muscle allows lateral movement and extension of the mid and lower back. This muscle is a common source of myofascial pain because of its frequent use in normal daily activities such as walking and sitting; it is made worse by poor posture.² Pain is felt in the flank, lower back, hip, and sometimes the buttocks but is mostly above the iliac crest and exacerbated by movement of the spine. It may mimic radicular or even sacroiliac joint pain because of its attachment to the iliac crest. Acute myofascial pain of the quadratus lumborum may be precipitated by sudden movements (e.g., lifting in a way that twists the lower back), and even the most mundane of movements such as coughing or deep breathing become painful. Even sleep can be problematic because patients are unable to find a comfortable position in which to sleep because of pain with any lateral movement of the spine. Patients describe pain with arising from the supine position. Because of its proximity to the abdominal organs, disease of these organs, particularly kidney disease, may present as low back pain and must be excluded. Pronounced asymmetry of the dominant quadratus lumborum in elite cricket players (fast bowlers) and resultant pars fractures involving the nondominant side have been reported in the literature in several case reports.¹² Pain from the quadratus lumborum may be confused with pain that comes from injury to the iliolumbar ligament.¹³ The iliolumbar ligament connects the transverse process of L5 to the iliac crest. This very strong, thick ligament stabilizes the L5 body to the ilium and prevents axial rotation and translational movement on the sacrum. Pain from the quadratus lumborum may be distinguished from pain caused by iliolumbar ligament injury because of the absence of pain around the area of the flank with iliolumbar pain. The quadratus lumborum lies deep to the erector spinae muscles and the thoracolumbar fascia, so it may be difficult to distinguish these muscles from the erector spinae just on the basis of palpation.¹⁴

Physical examination involves observation and palpation for trigger points. When the patient is standing, the practitioner should look from behind for obvious signs of spasm causing a functional scoliosis or tilt and should look for elevation of the posterior superior iliac spine. The practitioner should observe for an antalgic gait and palpate for tender trigger points just below the twelfth rib and around the area of the iliac crest; this may be increased with back rotation. Part of the physical examination includes looking for a functional leg length discrepancy caused by spasm of the quadratus lumborum. The shortened leg is associated with the side of quadratus spasm and subsequent contraction resulting in upward motion of the pelvis.¹⁵ Provocative maneuvers include palpation of trigger points while twisting the back.

Anatomy

The quadratus lumborum is shaped like a quadrangle and has as its origin the aponeurosis of the iliolumbar ligament and part of the iliac crest. It is posterior to the psoas muscle and lateral to the thoracolumbar fascia. It inserts at the twelfth rib and the transverse processes of L1 to L4. It serves as an anchor between the twelfth rib and the pelvis, and the majority of the fibers attach to the twelfth rib.¹⁶ This creates a stable base for the diaphragm, allowing for its function as a basic muscle of respiration.¹³ The quadratus lumborum pulls down on the diaphragm and laterally flexes the lumbar spine (unilateral) and aids in back extension (bilateral). Its innervation is from the ventral rami of T12 to L4.

Phillips et al ¹³ in their cadaver study of the anatomy of the quadratus lumborum showed that although there is considerable variation in the presence and location of the muscle fascicles, the muscle exists in three broad layers, and about half of the quadratus lumborum fascicles acts on the twelfth rib and the rest exert their actions on the lumbar vertebra. The compressive forces exerted by the quadratus lumborum is insignificant compared with that exerted by the erector spinae and multifidus, and thus there is little evidence for a major stabilizing role of the quadratus lumborum on the lumbar spine.¹³

Basic Science

There is no basic science information on quadratus trigger point injections.

Imaging

No special imaging is needed to make the diagnosis. This is a clinical diagnosis except to rule out other causes or bleeding or infectious reasons for the pain.

Guidelines

There are no printed guidelines for injections in the quadratus lumborum muscle.

Indications and Contraindications

The indication is myofascial low back pain with or without radiation to the hip with reproducible trigger points. It is contraindicated in situations in which muscular injections are contraindicated (e.g., coagulopathy or bleeding diathesis, localized infection at the site, or systemic infection).

Equipment

Materials for sterile prep and drape

25-gauge 2- or 3.5-inch spinal needles, depending on the size of the patient

Local anesthetic with or without a small amount of steroid diluted in the local anesthetic solution

Fluoroscopy machine or ultrasound machine if the patient is not overweight

Technique

Palpation of Trigger Points

Although in thin patients the quadratus may be theoretically palpated lateral to the erector spinae muscles and injected there, it is more accurate to perform these injections under fluoroscopic guidance. It is certainly reasonable to give a trial of trigger point injections based on palpation before performing the procedure under fluoroscopic guidance.

Quadratus Lumborum Trigger Point Injections Under Fluoroscopic Guidance

Sterile prep and drape of the area to be injected are done. The lateral border of the L4 transverse process is visualized under fluoroscopy. Needle entry is at the lateral inferior edge of the transverse process; the lateral aspect of the transverse process is touched with the needle tip. The needle is advanced approximately 1 cm or less, aiming to go just past the lateral edge of the transverse process. In the lateral view, the needle should not be anterior to the facetal line; bear in mind that the quadratus is just posterior to the posterior abdominal wall and anteriorly is the colon, psoas muscle, and kidneys. The kidney extends to approximately L3, so these injections are performed at L4. One mL of nonionic contrast solution is injected, and the striated appearance of contrast spread is visualized in the muscle along the quadratus lumborum muscle fibers. When it is clear that the needle is in the correct position and again after negative aspiration, local anesthetic is injected with or without steroid. The authors use a nonparticulate steroid, 5 mg of dexamethasone, but a low dose of particulate steroid (e.g., 20 mg of methylprednisolone diluted in the local anesthetic solution) may also be used. Good pain relief can be obtained with 5 to 7 mL of injectate; this may be done in a fanlike technique as long as intramuscular injection is confirmed. There should be no paresthesias, blood, or cerebrospinal fluid (CSF) with needle insertion.

The authors have not performed these injections under ultrasound guidance; however, an anatomical study ¹⁷ has been done involving the use of ultrasound guidance to identify the psoas and quadratus lumborum and erector spinae muscles. The study showed that these muscles are readily identified under ultrasonography, but this technique is not easily translated to overweight (body mass index, 25 to 29.9 kg/m²) or more obese patients. These authors identified the lumbar spinal levels by counting the images of the transverse processes starting at the level of the sacrum and proceeding in a cephalad direction. When using ultrasonography, the landmarks are first identified using the longitudinal view, where the probe is placed approximately 3 cm parallel to the spinous processes, then when at the desired level, rotating the probe to the short-axis or transverse view.¹⁷

Patient Management and Evaluation

For the best outcome, these injections are done in conjunction with physical therapy. Because other interventions may be responsive to steroid injections, injection of steroid should be kept to a minimum. As with other trigger point injections, the duration of action of the trigger point injections generally outlasts the duration of the local anesthetic, and in the authors’ experience, it varies with the time from symptom onset to injection.

Outcomes Evidence

There is sparse literature on outcomes from quadratus lumborum injections; they are virtually all anecdotal.

Risk and Complication Avoidance

The quadratus has its origin at the iliac crest and iliolumbar ligament and inserts around the twelfth rib and the transverse processes of the lumbar vertebrae. It is posterior to the kidney, so injection, particularly in thin patients, should be done with this in mind.

Iliopsoas Muscle Injections

Establishing the Diagnosis

The major role of the iliopsoas, supported by EMG evidence, is the main hip flexor of the body.¹⁸ Pain coming from the iliopsoas, when ipsilateral, is close to the midline but described as being vertical along the spinal column, sometimes radiating to the groin. Occupations that require patients to sit for many hours (e.g., driving for long hours daily), particularly with their knees above their hips, leave the iliopsoas in prolonged contraction and subsequent possibility of pain.¹ The psoas muscle is continuously active with prolonged sitting or standing, but the iliacus muscle is relatively inactive during standing.¹ Patients often describe pain in the lower back when changing positions from sitting to standing, particularly arising from a deep seated chair. Coughing and deep breathing do not cause pain as they do with myofascial pain of the quadratus lumborum. Patients often elect to sleep in the fetal position at night, but they awaken from the fetal position and extend the back to get out of bed, thereby stretching the iliopsoas muscle. Iliopsoas pain may radiate to the hip and anterior thigh. Pain involving the iliopsoas bursa can be an important source of unilateral hip and groin pain. Iliopsoas muscle tendinitis is seen with activities that require repetitive hip flexion and may result in a snapping hip. Iliopsoas bursitis is seen with overuse injuries in gymnasts and uphill runners and cyclists, presenting with anterior hip and groin pain.¹⁹ Lumbar spinal stenosis most often affects L4-L5 then L3-L4 levels. Iliopsoas weakness, which may present as difficulty climbing stairs, has been described as an early sign of lumbar spinal stenosis because of its innervations by the muscles of the lumbar plexus.²⁰

As with quadratus lumborum, myofascial pain involving the psoas muscle is a clinical diagnosis based on history and physical examination. Pathological processes involving the psoas muscle can be ruled out radiographically (e.g., hematoma and abscess). The physical examination starts with observation of the patient, including observation of the gait to look for an antalgic gait. It is difficult to palpate the iliopsoas muscle from the back, so provocative maneuvers will help with the diagnosis. The Thomas test, or inability to straighten the knee with the contralateral leg flexed while the patient is supine, has a positive result with a tight, contracted iliopsoas muscle. Pain is more often felt when rising from a seated position. Active straight-leg raise or resisted knee flexion causes pain. Prone hip extension that results in psoas stretch may also be painful. With iliopsoas bursitis, pain is felt with palpation at the insertion site in the femoral triangle at the lesser trochanter with the knee bent in the position used for the FABER (flexion abduction external rotation) test. Iliopsoas function is tested by passive testing of hip flexion strength; pain elicited by this maneuver may emanate from the iliopsoas.²¹

The iliopsoas muscle can cause hip pain because of snapping hip syndrome. One cause of this syndrome is the iliopsoas tendon’s slipping over the lesser trochanter at the level of the osseous ridge. Pain is often felt in the groin and anterior thigh, and clicking is heard when the hip is extended, adducted, and laterally rotated. Otherwise, pain from the iliopsoas muscle is felt lateral to the lumbar spine and in the anterior thigh.

Anatomy

The iliopsoas is a combination of the psoas major, psoas minor, and iliacus muscles. The psoas major has its origin along the anterolateral vertebral column at the levels of T12-L4 and passes under the inguinal ligament to attach, along with the iliacus, as the iliopsoas muscle on the lesser trochanter of the femur. There is a large iliac bursa, which sometimes communicates with the hip joint.¹⁴ The psoas minor is only variably present in a segment of the population and has its origin along the transverse processes of L1-L5; it is anterior to the psoas major. The iliacus muscle originates in the iliac fossa of the pelvis and occupies the anterior portion of the pelvic brim. The psoas major combines with the iliacus muscle at approximately the level of the inguinal ligament and inserts on the lesser trochanter of the femur to become the functional unit called the iliopsoas muscle. The iliopsoas muscle is the most powerful thigh flexor in the body, which is its main function. It lies deep or anterior and medial to the quadratus lumborum. The iliopsoas muscle is covered by the iliacus fascia. It is only directly palpable at the level of the femoral triangle.

The psoas major (ventral rami of L1-L3) and the iliacus (L2 and L3) share similar sources of innervations. The lumbar plexus is embedded in the psoas major. The iliacus muscle lies along the side of the psoas major and attaches to the tendon of the psoas major distally. The iliacus muscle is innervated by the femoral nerve (L2-L4) and the psoas major by the lumbar plexus (L1-L4). The psoas muscle is more associated with the leg and the quadratus with the hip.

The psoas muscles are arranged in a very homogenous fashion such that the bundles from each of the individual segments are of the same length. Compared with its function as the major hip flexor, its significance with respect to the lumbar spine is limited except to use the lumbar spine as a base for its action on the hip.^16,²² It is unique as a primary muscle of the leg in that its origins are from the lumbar spine.²² It has very little influence in lumbar flexion or extension; however, the psoas muscle does exert significant stress on the lumbar spine in the form of tremendous axial compressive and shear forces on the lower lumbar spine, particularly at the L5-S1 disc space. It also serves to increase the lumbar lordosis of the spine. This is maximized in activities that contract the psoas (e.g., sit-ups).²² EMG activity is controversial as to whether the iliopsoas plays some role in lateral rotation of the femur.^14,¹⁹ The psoas major is innervated by the anterior (ventral) rami of L1-L3. The nerves of the lumbar plexus pass through the psoas major on route to the lower extremity.

Basic Science

Imaging

No special imaging is needed to make the diagnosis; this is a clinical diagnosis.

Guidelines

There are no published guidelines regarding iliopsoas injections.

Indications and Contraindications

Equipment

Materials for sterile prep and drape

3.5-inch spinal needle

Local anesthetic with or without a small amount of steroid diluted in the local anesthetic solution

Fluoroscopy machine

Technique

Patient Management and Evaluation

For the best outcome, these injections are done in conjunction with physical therapy. Because some other interventions may be responsive to steroid injections, injection of steroid should be kept to a minimum.

Outcomes Evidence

There is no outcomes evidence published.

Risk and Complication Avoidance

The iliopsoas muscle is lateral to the vertebral foramen and posterior to the lumbar sympathetic chain and the great vessels of the abdomen, so caution with needle depth is important. The needle is directed perpendicularly, avoiding the foramen medially.

Evaluation and Treatment of Pain from the Piriformis Muscle

Establishing a Diagnosis

Piriformis syndrome is a diagnosis that is often difficult to determine and can lead to misdiagnosis. Because the symptomatology is so variable and so similar to many more common pain pathologies, piriformis syndrome is often a diagnosis of exclusion. The differential diagnosis includes lumbosacral facet syndrome, sacroiliac joint arthropathy, hip arthritic conditions (including greater trochanteric bursitis), and even organic causes such as pelvic masses.

The most common complaint with piriformis syndrome is gluteal (buttock) pain. Nearly the entire buttock (spanning from the sacral margin to the greater trochanter) can be painful and tender. This pain is usually made worse with prolonged sitting (classic complaint of pain during a long car ride) and with sit-to-stand transfers.²³ It is rare to have associated axial back pain, although occasionally there can be associated paraspinal lumbar pain.²³ Furthermore, the gluteal pain may radiate into the entire posterior thigh proximal to the knee as a function of posterior cutaneous nerve of the thigh irritation.²⁴ If there is associated irritation of the entire sciatic nerve, symptoms can even extend all the way into the toes, although it is not common to develop true focal neurological deficits. Interestingly, because of the anatomical closeness of the piriformis muscle with the pelvic and abdominal walls, symptoms can occur with bowel movements and sexual activity.²³

Historically, in about 50% of patients, there is an antecedent trauma. The traumatic event is not always direct trauma to the area, and there may be a lag of several months from the inciting trauma to the presentation of classic symptoms. The etiology of piriformis syndrome can even be total hip arthroplasty or spinal surgery.²⁵ Other causes are quite variable and include true leg length discrepancy (and associated gait abnormality and pelvic tilt), idiopathic piriformis hypertrophy, and altered piriformis anatomy.^26,²⁷

On examination, piriformis tenderness can be elicited with deep palpation, and a spindle-shaped mass may be felt in the buttock.²³ Although not specific for piriformis syndrome alone, symptoms are exacerbated by hip flexion, adduction, and internal rotation. Straight-leg raise results may or may not be positive based on whether or not the sciatic nerve is significantly affected. Sensory, motor, and reflex testing are almost always normal.²³ Three tests that have more specificity for piriformis syndrome are the Pace sign, Lasègue sign, and Freiberg sign:

Pace sign: pain and weakness with seated abduction of the hip against resistance ²⁸

Lasègue sign: pain with unresisted flexion, abduction, and internal rotation of the hip ²⁹

Freiberg sign: pain with forced (i.e., against resistance) internal rotation of the hip with the thigh fully extended ³⁰

Anatomy

The proximal insertions of the piriformis muscle include the S2-S4 sacral vertebra, the sacroiliac joint capsule, and the posterior iliac spine.²⁶ From these insertions, the muscle spans laterally through the greater sciatic foramen and attaches distally to the medical surface of the greater trochanter. Innervation to the piriformis muscle is provided by the L5, S1, and S2 spinal nerves. The sciatic nerve (either in divided or undivided form) passes directly through the muscle, under the muscle (most commonly), or above the muscle in very close proximity. The gluteal nerves and vessels and the posterior cutaneous nerve to the thigh also traverse below the muscle.²³

Basic Science

Imaging

Although magnetic resonance imaging (MRI) and computed tomography (CT) may show an enlarged piriformis muscle,³² piriformis syndrome still is truly a clinical diagnosis made with thorough history and physical examination. Depending on the cut of the MRI and the fluctuations in muscle swelling and reactivity, the imaging study results may be negative despite significant disease of the tissue.

Guidelines

There are no printed guidelines for injections in the piriformis muscle.

Indications and Contraindications

The indication for a piriformis injection is gluteal pain (and associated symptoms) with historical and examination findings suggestive of piriformis muscle irritation. Piriformis injection is contraindicated with local site or systemic infections and any bleeding diathesis or coagulopathy. Because this structure is deep (and noncompressible) and in such close proximity to a major neural structure (the sciatic nerve), it is recommended to use all precautions that are used for a deep nerve block. Also, because fluoroscopic guidance is needed, piriformis injection is contraindicated in pregnant women.

Equipment

Materials for sterile prep and drape

25-gauge 5- or 7-inch insulated nerve block needles, depending on the size of the patient

Local anesthetic with or without a small amount of steroid diluted in the local anesthetic solution

Fluoroscopy machine

Nerve stimulator

Radiographic contrast medium

Technique

In the technique described by Benzon et al,³¹ the patient is placed prone on a fluoroscopy table, and the inferior margin of the sacroiliac joint is imaged and marked. Then an insulated block needle is inserted 1 to 2 cm caudad and 1 to 2 cm lateral to the inferior margin of the sacroiliac joint. The insulated needle should be advanced with the nerve stimulator on until a sciatic nerve–evoked motor response is achieved (dorsiflexion, plantarflexion, eversion, inversion). The needle is slightly withdrawn until the sciatic stimulation disappears. Steroid (40 mg of either methylprednisolone or triamcinolone) plus 5 mL of saline is injected perisciatically. The needle is pulled back 1 cm (into the belly of the piriformis muscle), and the contrast is injected (Fig. 22-4). The contrast should outline the piriformis muscle belly, which will either appear as one single muscle unit or two muscle bellies if the piriformis is split by the sciatic nerve. After the characteristic dye spread is achieved, local anesthetic solution and steroid are administered. Typically, good pain relief can be attained with an injection of 5 mL of 0.5% bupivacaine plus 40 mg of methylprednisolone (or triamcinolone).

Fig. 22-4 The piriformis muscle is outlined after contrast injection.

A similar technique has been described using CT guidance, but the lack of readily available CT suites and the added radiation hazard limit this technique.³³ Further, similar blind techniques have been described as well as a perisciatic stimulator approach without fluoroscopic guidance.³⁴ Similarly, the piriformis muscle can be visualized with ultrasound although this requires a higher level of expertise with the ultrasound machine, especially in the obese patient.

Patient Management and Evaluation

Rarely, immediately after injection, the patient may develop a sciatic nerve block. This is reason for using saline, not local anesthetic, as the diluent for the perisciatic injection. Sciatic nerve block may still occur from leakage of the local anesthetic from the piriformis muscle or if the needle is not withdrawn far enough into the belly of the muscle. When sciatic nerve block occurs, the patient should be discharged with crutches (or a wheelchair) into the custody of an adult companion. In the long term, injections combined with physical therapy work best. Therapy should focus on correcting any sort of gait abnormality and pelvic tilt or obliquity as well as general core strengthening.

Outcomes Evidence

Using the technique described, Benzon and colleagues ³¹ were able to achieve some short- or long-term relief of symptoms in 16 of 19 patients. It should be noted that most of these patients had fairly severe and chronic pain with multiple pain generators (not isolated piriformis syndrome).