Abstract
Pain syndromes that can be attributed to deep muscles are often caused by mechanical impingement of the muscular tissue upon traversing neurovascular structures. The most common of these disorders include piriformis syndrome, in which the piriformis muscle may compress the sciatic nerve, and thoracic outlet syndrome (TOS), in which the scalene musculature compresses the brachial plexus. In contrast, iliopsoas-related pain is not related to compression or irritation of the nerve. However, all three of these pathophysiologic states can be managed through conservative measures, injection therapy, or surgical intervention. Conservative measures typically include multimodal treatment with antiinflammatory analgesics, muscle relaxants, and physical therapy. If these fail, injections of local anesthetic, steroid, or botulinum toxin into the muscles causing irritation are often a second-line option. Surgery is typically reserved for refractory cases with significant negative impact upon a patient’s functional status.
Keywords
botulinum toxin, deep muscle injection, fluoroscopic guidance, iliopsoas pain, piriformis syndrome, thoracic outlet syndrome, ultrasound guidance
Introduction
Pain syndromes that can be attributed to deep muscles are often caused by mechanical impingement of the muscular tissue upon traversing neurovascular structures. The most common of these disorders include piriformis syndrome, in which the piriformis muscle may compress the sciatic nerve, and thoracic outlet syndrome (TOS), in which the scalene musculature compresses the brachial plexus. In contrast, iliopsoas-related pain is not related to compression or irritation of a nerve. However, all three of these pathophysiologic states can be managed through conservative measures, injection therapy, or surgical intervention.
Piriformis Syndrome
Although piriformis syndrome is rare, occurring in only 5%–6% of patients that are referred for back or leg pain, the syndrome is often underrecognized and should therefore be considered in the differential diagnosis of patients that present with unilateral buttock and leg pain. A more detailed discussion of the syndrome may be referenced in Chapter 67 .
Diagnosis
There are no standardized diagnostic criteria for piriformis syndrome, and the pattern of pain produced is very similar to other more common pain generators such as lumbar facet arthropathy or herniated intervertebral disc. As such, piriformis syndrome is not only a clinical diagnosis but also a diagnosis of exclusion. It should be considered in the differential diagnosis of patients with unilateral buttock/leg pain, but clinical suspicion may be increased in the presence of several signs on physical exam. In contrast to other sources of lower extremity pain, typically patients with true piriformis syndrome do not exhibit low back pain. Common symptomatology includes an aching pain that localizes to the buttock, is unilateral, and radiates down to the posterior aspect of the leg, occasionally into the calf or foot. Piriformis syndrome may be more common in the setting of an aberrant relationship between the piriformis muscle and the sciatic nerve. Six different relationships exist; these are described in Chapter 67 . Aberration from the typical anatomy is also thought to decrease the likelihood that piriformis injections will be effective. Diagnosis of the syndrome is based on symptoms, physical examination findings, and a favorable response to a local anesthetic injection into the piriformis muscle.
Conservative Treatment
As with all pain syndromes, conservative management is attempted first for piriformis syndrome. Antiinflammatory agents and muscle relaxants used in conjunction with physical therapy are the first line of treatment in piriformis syndrome. Improved outcomes have been noted in patients that receive piriformis injection compared with those that receive only conservative management with physical therapy and medications. Therefore if a patient’s symptoms are not adequately treated with conservative measures, injection therapy is recommended as the next step in management.
Injection Treatment
Injection without the assistance of an imaging modality is technically challenging because the piriformis muscle is small in size and deep in anatomic location. Common methods of image guidance include ultrasound and fluoroscopy, which may be used alone or in tandem with electromyography (EMG). Techniques for injection using computed tomography (CT) have also been described but are not as useful clinically, given increased radiation exposure to the patient and increased duration of procedure. Regardless of choice of technique, the patient is placed in the prone position and vital signs are monitored throughout the procedure. A 20–22-gauge needle is used for the procedure, with an echogenic needle being preferable for ultrasound-guided technique and a stimulating needle if EMG is to be utilized. For all techniques, the area to be injected is cleansed with an alcohol-based cleaning solution and then the site of skin insertion and deeper tissues are anesthetized with 1% lidocaine.
Fluoroscopic Injection Techniques
The piriformis muscle can be injected either in its belly or its tendon. When injecting into the tendon, fluoroscopy in the anterior-posterior (AP) orientation is used to identify the proximal end of the femur. After appropriate sterile preparation, draping, and administration of local anesthesia, a needle is advanced to the insertion edge of the piriformis muscle on the greater trochanter. Contrast agent is then injected and observed to spread into the tendon, and after negative aspiration, a 5-mL volume of local anesthetic and steroid is administered.
There are two methods of injection into the belly of the muscle: sacroiliac joint landmark and acetabular landmark.
Sacroiliac Joint Landmark
The fluoroscope is positioned to view the sacroiliac joint (SIJ) in AP orientation. An area 2–3 cm caudal and 2–3 cm lateral to the inferior margin of the SI joint is marked and anesthetized with lidocaine. A needle is placed at this mark and inserted 5–7 cm into the musculature in coaxial alignment with the fluoroscope ( Fig. 80.1A ). The needle is then advanced in lateral view to the anterior margin of the sacrum and contrast medium is injected (see Fig. 80.1B ). An appropriate myogram outlining the piriformis is verified in AP view (see Fig. 80.1C ), and after negative aspiration, the steroid and an additional volume of local anesthetic is injected.
Acetabular Landmark
An alternative technique also targets the muscle belly but at a slightly more lateral location. The fluoroscope is initially positioned in AP view, with the center of the scope approximating the superomedial margin of the acetabulum. In coaxial orientation, the needle is advanced toward the anatomic “X” marking the junction of the line descending inferiorly from the greater sciatic notch and the curvature of the pelvic brim. The proceduralist must ensure that the needle tip remains lateral to the curvature of the pelvic inlet ( Fig. 80.2 ). The procedure is then conducted as described previously. Using this method, the needle is advanced toward bone, which is an added level of safety compared to the SIJ method, in which the needle is advanced through the pelvic inlet and care must be taken to avoid injury to soft tissue structures.
Combination Fluoroscopic and Nerve stimulation Technique
The piriformis muscle can be approached using the landmarks described previously (i.e., 2–3 cm caudal and 2–3 cm lateral to the inferior margin of the SI joint) or at the “X” junction of the pelvic brim and the ridge descending inferiorly from the greater sciatic notch. When using EMG in addition to fluoroscopic guidance, the 6–10-cm stimulating needle is connected to a nerve stimulator with settings of 2 Hz and 1 mA. Contraction of the gluteal muscles indicates that the needle is close and superficial (posterior) to the sciatic nerve and piriformis muscle. Proximity of the tip of the needle to the sciatic nerve results in plantar flexion, dorsiflexion, eversion, or inversion. The presence of one of these evoked motor responses at 0.2–0.4 mA implies close proximity of the needle tip to the nerve. The needle is withdrawn 2 mm to ensure that the needle is not intraneural, and 5 mL of steroid and saline (to avoid leg numbness) is injected. The needle is then withdrawn 1 cm and 1–3 mL contrast is injected, which should ideally outline the belly of the piriformis. Another 5 mL of steroid and local anesthetic is then injected.
Another technique involves drawing a line from the greater trochanter to the middle of the sciatic notch, and a mark is made at the midpoint of this line. The needle is inserted in a slightly lateral to medial trajectory and advanced until the needle tip makes contact with the ilium. The needle is withdrawn 1 cm and attached to a nerve stimulator set at 1 mA, 2 Hz, 0.2 ms. The needle is then manipulated with very small movements until the appropriate motor response, dorsiflexion, plantar flexion, eversion, and inversion of the ipsilateral foot is noted. The subsequent steps are then similar to the previously described technique. This technique is most often used when imaging methods are not accessible, but given the increasing availability of fluoroscopes and ultrasound machines, image guidance is now used in the majority of procedures.
Ultrasound-Guided Technique
As previously stated, the ultrasound-guided technique allows visualization of soft tissue, such as vasculature, the piriformis muscle itself, and the muscle’s relationship to the sciatic nerve. The ultrasound machine should ideally be equipped with a Doppler and be positioned on the contralateral side to the patient’s affected limb. Although the flat, high frequency transducer may be used in thin patients, a curved, low frequency (2–6 MHz) ultrasound probe is used more frequently to ensure adequate visualization of these deep structures.
Localizing the Piriformis Muscle
Method 1: To visualize the small, spindle-shaped piriformis muscle, the transducer is typically positioned in the short axis (transverse) view ( Fig. 80.3A ) over the sacroiliac joint, with the sacrum in view on the medial portion of the ultrasound screen and the ilium/gluteus maximus visible on the lateral view of the screen. Given that the muscle lies horizontally between the sacrum and greater trochanter of the femur, the transducer is then moved caudally such that the sacroiliac joint remains in the center of the screen but the lateral view of the ilium is out of view. This signifies that the transducer is positioned directly over the greater sciatic notch and the hyperechoic lateral aspect of the sacrum can be visualized medially. The operator should observe the large gluteus maximus muscle spanning the center of the image and, deep to this, the small, sardine-sized, piriformis muscle originating from the anterolateral sacral edge. If the transducer is manipulated inferiorly and rotated (clockwise if the injection is performed on the left and counterclockwise if the injection is performed on the right), then the sciatic nerve will become visible deep to the medial aspect of the piriformis (see Fig. 80.3B ). The inferior gluteal artery, medial to the sciatic nerve and anterior to the piriformis, should be identified and avoided during needle insertion. The ischium appears initially as a curved hyperechoic line (posterior acetabulum) and will then appear as a flat line deep to the piriformis as the probe is moved caudally.
FIG. 80.3
Ultrasound-guided piriformis muscle injection. (A) External view of the position of the ultrasound probe prior to piriformis injection. (B) The relationship between the piriformis muscle, gluteus maximus muscle and sciatic nerve as visualized under ultrasonography. (C) Optimal needle position immediately prior to intramuscular piriformis injection. (D) Shallow needle entry and advancement medially to position the needle tip for perineural injection of the sciatic nerve.
Method 2: An alternate method of locating the piriformis involves drawing a line connecting the greater trochanter and ischial tuberosity. The transducer is positioned over this line to identify the sciatic nerve. The nerve is followed cephalad until the gluteus maximus and piriformis are visualized superficial to the sciatic nerve.
Confirmation of Visualization
With the piriformis muscle in the center of the ultrasound screen, flex the ipsilateral knee to 90 degrees and rotate the hip both internally and externally. This maneuver will cause the piriformis to glide over the ischium while the gluteus maximus remains motionless. Other muscles that are similar in size and may be confused with the piriformis should be identified to ensure that the appropriate muscle is targeted for injection. A relatively simple way to make this distinction is visualization of the ischial spine, as only the gemelli and obturator muscles insert onto this anatomic landmark.
Needle Insertion
An area 3–4 cm from the lateral aspect of the transducer should be anesthetized with lidocaine. The echogenic needle is advanced, in plane with the ultrasound probe, in a lateral to medial and posterior to anterior direction into the gluteus maximus and the medial half of the piriformis. If the needle tip is difficult to visualize due to loss of resolution with increasing depth, hydrodissection may assist in confirming depth. When the needle is positioned in the piriformis muscle (see Fig. 80.3C ), then the injectate may be administered. If desired, the needle may then be advanced at a shallow angle and positioned in the fascial plane separating the piriformis from the sciatic nerve (see Fig. 80.3D ), where additional injectate may be administered.
Ultrasound and Electromyographic Guidance
After identification of the presumptive piriformis muscle using the technique described previously, EMG may be used to verify placement in the piriformis rather than surrounding musculature. If EMG is to be used concomitantly with ultrasound guidance, hydrodissection must be conducted with a nonelectrolyte solution, such as 50% dextrose, whereas normal saline may be used in a strictly ultrasound-guided procedure.
Postprocedure Monitoring
Patients may develop weakness/numbness in the distribution of the sciatic nerve following this injection. The patient should be cautioned that they have an increased risk of fall for the expected duration of the local anesthetic used and that they should not operate motor vehicles. The patient should also be advised that bleeding/bruising at the injection site may be normal. Adverse outcomes include local infection, bleeding/bruising, and other neurologic symptoms such as bowel/bladder incontinence. Signs and symptoms of these should prompt medical staff to send the patient to the emergency room.
Comparison of Techniques
Ultrasound-guided and fluoroscopic techniques for piriformis injection have not been shown to differ in terms of patient outcome measures, complication rate, or duration of procedure. However, this may be difficult to assess, given the already low rate of complications for these procedures. The advantage of ultrasound guidance includes visualization of soft tissue structures (e.g., vasculature), but resolution attenuates when attempting to visualize deeper structures such as the piriformis. This poor visualization is exacerbated by obesity or large body habitus, causing increased tissue depth between the ultrasound probe and the deep musculature.
Injectate
Injection of the piriformis muscle is deemed a trigger point injection when providers bill for the procedure, despite the more technically difficult nature of the injection. Often the injection is advertised as proffering analgesic efficacy for several months, but this duration will vary based on many patient factors, the number of injections in the series, and the injectate used. Common options include local anesthetic, steroid, and botulinum toxin. A common injection includes approximately 5 mL of 1% lidocaine with 40 mg of a particulate form of steroid, either methylprednisolone or triamcinolone. Water-soluble forms of steroid, such as dexamethasone or betamethasone, are another injectate option. Lastly, botulinum toxin may be administered, ordinarily as the sole agent, with a typical dose of 100 mouse units in 2 mL of normal saline. See Table 80.1 for a summary of injection studies for deep musculature.
| Muscle Injected | Author, Year of Publication | Number of Patients | Type of Study | Image Guidance | Injectate | Outcome |
|---|---|---|---|---|---|---|
| Piriformis | Porta, 2000 | 23 7 10 | RCT | CT | Methylprednisolone 80 mg or Btx-A 100 U piriformis 150 U iliopsoas 80 U ant. scalene | Improved pain in Btx-A group 60 days postinjection |
| Fanucci et al., 2001 | 30 | Prospective | CT | (ona) Btx-A 100 U | Improved pain with either 1 or 2 injections | |
| Fishman et al., 2002 | 21 | RCT double blind parallel | EMG | (abo) Btx-A 200 U | Majority of patients had >50% pain reduction | |
| Childers et al., 2002 | 9 | RCT double blind crossover | EMG + FL | (ona) Btx-A 100 U | Improved pain, distress, spasm, and functional status with Btx-A | |
| Fishman et al., 2004 | 27 | Prospective | EMG | Btx-B | Most patients had >50% relief at 3 months | |
| Lang, 2004 | 20 | Prospective open-label | EMG | Btx-B 5000 U | Improved pain 16 weeks postinjection | |
| Yoon et al., 2006 | 20 | Prospective | CT | (abo) Btx-A 150 U | Improvement in pain and functional status at 12 weeks | |
| Naja et al., 2009 | 19 | RCT double blind parallel | EMG CT verified | Clonidine 150 mcg + bupivacaine vs. bupivacaine alone | Clonidine improves pain compared to bupivacaine alone at 6 months | |
| Masala et al., 2012 | 23 | Prospective | CT | Methylprednisolone 40 mg | Improvement in pain at 12 months compared with control | |
| Michel et al., 2013 | 122 | Prospective | EMG | (ona) Btx-A 50–100 U | Most patients had good or very good results from injection | |
| Al-Al-Shaikh et al., 2015 | 12 | Retrospective | Ultrasound/CT | (ona) Btx-A | Improvement in pain | |
| Albayrak et al., 2015 | 28 | Prospective | FL | Methylprednisolone, unknown dose | Improvement in pain and functional status | |
| Jeong et al., 2015 | 63 | Retrospective | Ultrasound | 40 mg of triamcinolone | Improvement in pain in majority of patients | |
| Misirlioglu et al., 2015 | 47 | RCT double blind | Ultrasound | Lidocaine 2% vs. Lidocaine + betamethasone | Improvement in pain in both groups |
| Muscle Injected | Author, Year of Publication | Number of Patients | Type of Study | Image Guidance | Injectate | Outcome |
|---|---|---|---|---|---|---|
| Iliopsoas | Porta, 2000 | 7 | RCT | CT | Methylprednisolone 80 mg or Btx-A 100 U piriformis 150 U iliopsoas 80 U ant. scalene | Improved pain in Btx-A group 60 days postinjection |
| Nunley et al., 2009 | 19 | Retrospective | FL | Triamcinolone 40 mg + local anesthetic | Improvement of pain in the majority of patients | |
| DeAndres et al., 2013 | 27 | RCT | FL | Btx-A 50 U | Improvement in pain at 3 months | |
| Liu et al., 2014 | 37 | RCT | US | Btx-A, weight-based dosing (pediatric study) | Improvement in motor function and gait compared to PT alone | |
| Rosseaux et al., 2014 | 11 | Prospective open label | EMG | (ona) Btx-A 300 or 400 U | Improvement in comfort, hypertonia, and passive ROM | |
| Agten et al., 2015 | 39 | Prospective | FL | Triamcinolone 40 mg | Improvement in pain, functional status at 1 month |
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