Piriformis Injection

Piriformis syndrome is a common cause of buttock and posterior leg pain. Pain in these areas can begin spontaneously or after an injury. The symptoms are commonly seen in patients with other inflammatory conditions and in patients who sit for most of their work day.

The pain usually begins when the piriformis muscle becomes taut, tender, and contracted. This process causes a deep aching sensation in the midgluteal region that is sometimes associated with pain radiating down the posterior leg or up to the lower back. The tight piriformis may cause a nerve and vessel entrapment syndrome as a consequence of its close proximity to the sciatic nerve and surrounding vessels.

Piriformis syndrome may constitute as many as 6-8% of low back pain conditions associated with sciatica.[1] Some patients experience symptoms in all five toes (multiple dermatomes) rather than in either lateral toes (S1 radiculopathy) or medial toes (L5 radiculopathy), as is generally the case in patients with herniated lumbar discs. The straight-leg raise (SLR) test is generally negative. Pain in the gluteal area is the predominant symptom. Numbness or weakness is rare.[2]

Piriformis syndrome is frequently a diagnosis of exclusion. Before the diagnosis is made, other causes of gluteal, hip, and leg pain must be ruled out (see Periprocedural Care). Michel et al created a 12-point clinical scoring system for standardization of the diagnosis and development of a treatment plan for piriformis syndrome.[3]

Many forms of therapy, medication, and injections have been used effectively to alleviate the pain associated with piriformis syndrome. This topic describes the most commonly piriform injection techniques (see Technique).[4]

Patients who do not improve with a conservative regimen of piriformis stretching, physical therapy, and administration of nonsteroidal anti-inflammatory drugs (NSAIDs) or other analgesics are candidates for piriformis injection.[5]

Contraindications for piriformis injection include the following:

• Local infection
• Bleeding disorders

Anatomy

The piriformis exits the pelvis through the greater sciatic foramen and inserts on the greater trochanter of the femur. The obturator internus exits the pelvis by passing through the lesser sciatic foramen; it also inserts on the greater trochanter of the femur. Both muscles assist in the external rotation and abduction of the thigh.[6]

The primary symptom of piriformis syndrome is buttock pain, with or without posterior thigh pain, that is aggravated by sitting or activity. Associated low back pain is common and can be a result of piriformis pain, but it can also suggest the involvement of other structures, such as facet joints or iliopsoas muscles. In an isolated piriformis syndrome, the major findings include buttock tenderness from the sacrum to the greater trochanter and reproduction of buttock pain on prolonged hip flexion, adduction, and internal rotation.[7]

Pain is often referred down the posterior portion of the leg, following the distribution of the tibial and peroneal branches of the sciatic nerve. These branches become inflamed as they pass over, under, or through the tight piriformis. Pain is thought to be caused by myotendinous breakdown of the piriformis, as well as by focal demyelination of the affected branches of the sciatic nerve.

The piriformis is usually tight and contracted, with focal trigger-point tenderness on palpation. Piriformis syndrome is frequently associated with sacroiliac dysfunction and leg length discrepancies.

Best practices

To decrease bruising and hematoma formation, the patient should be asked to stop taking NSAIDs (eg, ibuprofen and naproxen) 5 days before the procedure, if possible. This is helpful but not required.

For the best long-term relief, piriformis injection should be followed by a month of physical therapy (see Piriformis Syndrome).

Complication prevention

Sciatic injury can be largely avoided by advancing the needle slowly and asking the patient to report any tingling, numbness, electrical sensations, or pain down the back of the leg. At the first signs of discomfort, the needle should be pulled back and then redirected laterally. Injecting in the outer third of the muscle also lowers the chance of sciatic nerve injury.

Before the diagnosis of piriformis syndrome is made, other causes of gluteal, hip, and leg pain must be ruled out. Various physical testing maneuvers are helpful in making a diagnosis. One such maneuver consists of flexion, passive adduction, and internal rotation of the involved hip with the patient standing (see the first image below) or reclining (see the second and third images below).

Testing for piriformis pain. Involved hip is flexed, passively adducted, and internally rotated with patient standing.

Testing for piriformis pain. Involved hip is flexed, passively adducted, and internally rotated with patient reclining.

Testing for piriformis pain. Involved hip is flexed, passively adducted, and internally rotated with patient reclining.

The Freiberg test (see the first image below) and the Beatty maneuver (see the second image below) are also commonly performed to test for piriformis pain.[8]

Freiberg test. Forceful internal rotation of thigh on affected side elicits pain.

Beatty maneuver. Patient lies on uninvolved side and abducts involved thigh upward, which elicits pain.

Equipment that may be employed in piriformis injection includes the following:

• Needle (25 gauge; 0.75 in.)
• Needle (22 gauge; 2, 4, or 6 in.)
• Needle (18 gauge; 1.5 in.)
• Syringe (3 mL)
• Two syringes (10 mL)
• Intravenous (IV) extension set
• Metal marker or clamp
• Bandage or appropriate dressing
• Electromyography (EMG) disposable injectable monopolar needle (if EMG localization is being used; see Technique)

Medications that may be required include the following:

• Iohexol
• Normal saline (preservative-free)
• Lidocaine 1%
• Ropivacaine or bupivacaine 0.5% (preservative-free)
• Corticosteroids (preservative-free and water-soluble), such as methylprednisolone or triamcinolone diacetate
• OnabotulinumtoxinA

Piriformis injection is done with local anesthesia. Typically, 5 mL of 1% lidocaine is infiltrated into a skin wheal. As the needle is advanced, the remaining lidocaine is infiltrated along the path of the needle, as needed. (See Local Anesthetic Agents, Infiltrative Administration.)

Naja et al investigated whether clonidine-bupivacaine nerve-stimulator–guided injections are effective in achieving long-lasting pain relief in piriformis syndrome as compared with bupivacaine-guided injection.[9] Significantly lower pain scores and analgesic consumption were observed with bupivacaine-clonidine than with bupivacaine-saline. Additionally, pain at 6 months was significantly greater in the bupivacaine-saline group (78%) than in the bupivacaine-clonidine group (8%).

The procedure is done with the patient in a prone position.

There are three main techniques commonly used for piriformis injection, differentiated according to the modality employed for localization, as follows:

• Injection under fluoroscopic guidance
• Injection under ultrasonographic (US) guidance
• Injection under electromyographic (EMG) guidance

Computed tomography (CT) is rarely used to guide piriformis injection because it exposes the patient to unnecessary radiation. If a fluoroscope is not available, CT may be used as a substitute; the technique is essentially the same as with fluoroscopy.

In any of the techniques described below, 100 U of onabotulinumtoxinA may be infiltrated instead of the combination of triamcinolone with bupivacaine or ropivacaine. A 50 U/mL dilution with preservative-free normal saline is recommended.

For piriformis injection under fluoroscopic guidance, the patient is first placed in a comfortable prone position, with the C-arm positioned to provide an anteroposterior view of the affected side.[10] The sacrum and the greater trochanter are identified and used as medial and lateral bony landmarks, respectively (see the image below).

Fluoroscopy-guided piriformis injection. Greater trochanter and lateral border of sacrum are identified fluoroscopically and used as markers for needle insertion.

The skin is prepared with three consecutive povidone-iodine scrubs. A skin marker may be used to draw a line from the posterior inferior iliac spine to the greater trochanter. The estimated skin entry site is at the midpoint of this line.

Local anesthesia, both superficial and deep, is provided through local infiltration of 1% lidocaine buffered with sodium bicarbonate. The needle is advance to a bony end point and then withdrawn. Proper needle placement is confirmed by injecting a contrast solution, which should delineate the contour of the piriformis (see the image below).

Fluoroscopy-guided piriformis injection. Anteroposterior fluoroscopic image of piriformis after contrast administration.

Once needle placement is confirmed, a diagnostic or therapeutic block may be carried out. Diagnostic blocks are performed with 1 mL of 1% lidocaine and 3 mL of 0.5% ropivacaine or bupivacaine. After a diagnostic block, the patient may be examined to evaluate for pain and hip function. Therapeutic blocks are performed with 3 mL of 0.5% ropivacaine or bupivacaine combined with 40 mg of triamcinolone.

For piriformis injection under US guidance, a linear ultrasound probe is positioned with its lateral side medial to the greater trochanter and its medial side lateral to the ischial tuberosity.[8, 11] In this position, the sciatic nerve is identified as an oval honeycombed structure with mixed echogenicity. The sciatic nerve is then followed cephalad until it courses beneath the piriformis and deviates medially toward the sacrum. (See the image below.)

Ultrasound-guided piriformis injection. Greater trochanter and lateral border of sacrum are identified. Ultrasound probe is directed parallel to piriformis. Needle is inserted in lateral third of piriformis.

Once the relation between the sciatic nerve and the piriformis has been determined, an entry point is identified on the piriformis lateral to this intersection. At this point, the linear probe is positioned parallel to the piriformis fibers in such a way that the needle is in an in-plane orientation. The gluteus maximus and the piriformis are visualized and demarcated by a sheath that appears as a hyperechoic band (see the image below).

Ultrasonogram identifies sciatic nerve, gluteus, and piriformis.

The needle is then advanced under US visualization, traversing the gluteus maximus and piercing the piriformis.

For piriformis injection under EMG guidance, insert a disposable injectable monopolar needle electrode (23-25 gauge; 2-5 in.) is inserted at the midpoint of a line drawn from the posterior superior iliac spine to the greater trochanter. The needle should touch bone and then be withdrawn slightly.

Piriformis recruitment is tested by means of external rotation of the thigh. Once needle placement is confirmed, 40 mg of triamcinolone, together with 2-3 mL of 0.5% ropivacaine or bupivacaine, is infiltrated into the muscle.

Potential complications after piriformis injection include the following:

• Infection or abscess at the injection site
• Sciatic neuropathy due to direct injection into the nerve
• Bleeding or hematoma formation at the injection site ^[12]
• Temporary leg weakness and numbness if the local anesthetic causes a nerve block - To address this possibility, the patient should receive a neurologic evaluation before driving home

The goal of pharmacotherapy is to provide local anesthesia, both superficial and deep, prior and throughout the procedure.

Class Summary

Local anesthetic agents are used to increase patient comfort during the procedure.

Lidocaine (Xylocaine)

Lidocaine is an amide local anesthetic. This agent inhibits depolarization of type C sensory neurons by blocking sodium channels. It is provided by means of local infiltration of 1% lidocaine buffered with sodium bicarbonate.

Bupivacaine (Marcaine, Sensorcaine)

Bupivacaine 0.25% may be used in combination with lidocaine plus epinephrine (50:50 mixture). It decreases permeability to sodium ions in neuronal membranes. This results in the inhibition of depolarization, blocking the transmission of nerve impulses.

Ropivacaine (Naropin)

Ropivacaine decreases permeability to sodium ions in neuronal membranes. This results in the inhibition of depolarization, blocking the transmission of nerve impulses. This agent is an option for longer postoperative analgesia. The onset is delayed from 5 minutes to about 20 minutes.