Piriformis Injection 

Piriformis syndrome is a common cause of buttock and posterior leg pain. Typically, the piriformis muscle becomes taught, tender, and contracted. This causes a deep aching sensation in the mid-gluteal region that is sometimes associated with pain radiating down the posterior leg. The tight piriformis muscle may cause a nerve and vessel entrapment syndrome because of its close proximity to the sciatic nerve and surrounding vessels.

The piriformis muscle 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 same movement of the thigh (external rotation and abduction).^[1]

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 suggests 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.^[2]

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 muscle. Pain is thought to be caused by myotendinous breakdown of the piriformis muscle, as well as by focal demyelination of the affected branches of the sciatic nerve. The piriformis muscle is usually tight and contracted, with focal trigger point tenderness on palpation. Piriformis syndrome is frequently associated with sacroiliac dysfunction and leg length discrepancies.

Piriformis syndrome may constitute up to 6-8% of low back pain conditions associated with sciatica.^[3] However, patients typically experience symptoms in all 5 toes (multiple dermatomes) rather than in lateral toes (S-1 radiculopathy) or medial toes (L-5 radiculopathy), as is commonly seen in patients with herniated lumbar discs. The straight-leg raise (SLR) test is generally negative, and pain is the predominant symptom; numbness or weakness is rare.^[4]

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. The following piriformis testing maneuvers are helpful in making a diagnosis (see images below):

The Freiberg test and Beatty maneuver are also commonly used to test for piriformis pain (see images below).^[5]

Many forms of therapy, medication, and injections have been used effectively to alleviate piriformis syndrome pain. This article describes the most commonly used injection techniques.

• Patients whose condition does not improve with a conservative regimen of piriformis stretch, physical therapy, nonsteroidal antiinflammatory drugs (NSAIDs), and analgesics are candidates for piriformis injection.^[6]

• Local infection
• Bleeding disorders

• Local anesthetic is used for piriformis injection.
• 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.
• Naja et al investigated whether clonidine-bupivacaine nerve-stimulator – guided injections are effective in achieving long-lasting pain relief in piriformis syndrome compared with bupivacaine-guided injection. Significantly lower pain scores and analgesic consumption were observed with bupivacaine-clonidine compared with bupivacaine-saline (P< 0.0001). Additionally, pain at 6 months was significantly greater in the bupivacaine-saline group (78% compared with the bupivacaine-clonidine group (8%).^[7]
• For more information, see Local Anesthetic Agents, Infiltrative Administration.

Equipment

• Needle, 25 gauge (ga), 0.75 inch
• Needle; 22 ga; 2, 4, or 6 inch
• Needle, 18 ga, 1.5 inch
• Syringe, 3 mL
• Syringes, 10 mL (2)
• Intravenous extension set
• Metal marker/clamp
• Bandage or appropriate dressing
• Electromyelography (EMG) disposable injectable monopolar needle (if using EMG localization)

Medications

• Iohexol (Omnipaque) 200-300
• Normal saline (NaCl 0.9%), preservative free
• Lidocaine 1%
• Ropivacaine or bupivacaine 0.5%, preservative free
• Corticosteroids, preservative free and water soluble (eg, methylprednisolone, triamcinolone diacetate)
• Botulinum toxin type A (BOTOX®)

• The patient is placed in a prone position.

Three commonly used injection techniques are described below: guidance with fluoroscopy, ultrasonography, or electromyelography (EMG).

Fluoroscopic guidance

• Using fluoroscopic guidance, place the patient in a comfortable prone position with the C-arm positioned in an anteroposterior view of the affected side.^[8] The sacrum and greater trochanter are used as medial and lateral bony landmarks, respectively (see image below). Greater trochanter and lateral border of sacrum identified fluoroscopically.
• Prepare the skin with 3 consecutive povidone-iodine scrubs.
• Using a skin marker, a line may be drawn 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 with local infiltration of 1% lidocaine buffered with sodium bicarbonate. Advance the needle to a bony end point and then withdraw. Confirm proper needle placement with injection of a contrast solution, which should delineate the contour of the piriformis muscle (see image below). Anteroposterior fluoroscopic image of the piriformis muscle after contrast administration.
• Once needle placement is confirmed, a diagnostic and therapeutic block may be performed.

  • 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.

Ultrasonographic guidance

• Using an ultrasound-guided technique, initially position a linear probe with its lateral side medial to the greater trochanter and the medial side lateral to the ischial tuberosity.^[5] In this position, the sciatic nerve is identified as an oval, honeycomb structure with mixed echogenicity. Follow the sciatic nerve cephalad until it courses beneath the piriformis muscle and deviates medially toward the sacrum. See image below. Greater trochanter and lateral border of sacrum identified by ultrasonography. The ultrasound probe directed parallel to the piriformis muscle. Needle insertion is in the lateral third of the piriformis muscle.
• Having identified the relationship between the sciatic nerve and the piriformis muscle, identify an entry point on the piriformis muscle lateral to this intersect.
• At this point, position the linear probe parallel to the piriformis muscle fibers such that the needle is in an in-plane orientation. The gluteus maximus and piriformis muscles are visualized and demarcated by a sheath that appears as a hyperechoic band. See image below. Ultrasound image identifying the sciatic nerve, gluteus, and piriformis muscle.
• Advance the needle with ultrasonographic visualization, traversing the gluteus maximus and piercing the piriformis muscle.

EMG guidance

• Under EMG guidance, insert a disposable injectable monopolar needle electrode (23-25 ga, 2-5 in) 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.
• Test piriformis muscle recruitment by external rotation of the thigh.
• Following confirmation of needle placement, infiltrate 40 mg of triamcinolone combined with 2-3 mL of 0.5% ropivacaine or bupivacaine into the muscle.

• To decrease bruising and hematoma formation, ask patient to stop taking NSAIDs (eg, ibuprofen, naproxen) 5 days before the procedure, if possible. This is helpful but not required.
• For the best long-term relief, follow the injection with a month of physical therapy. For more information, see Physical Medicine and Rehabilitation article Piriformis Syndrome.
• Avoid sciatic injury 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, simply pull back and redirect the needle laterally. Injecting in the outer third of the muscle lowers the chance of sciatic nerve injury.
• CT is rarely used because it exposes the patient to unnecessary radiation. If a fluoroscope is not available, CT may be used as a substitute, using the same technique as with fluoroscopy.^[9]
• Botulinum toxin type A: In any of the above techniques, 100 units of botulinum toxin type A may be infiltrated instead of the triamcinolone/bupivacaine injection described. A 50 U/mL dilution with preservative-free normal saline is recommended.
• Use sterile technique.

• Infection or abscess at the injection site
• Sciatic neuropathy due to direct injection into the nerve
• Bleeding or hematoma formation at the injection site^[10]
• Temporary leg weakness and numbness if the local anesthetic causes a nerve block (The patient should receive a neurologic evaluation prior to driving home.)