Piriformis Injection

The piriformis muscle originates from the anterior surface of the second through fourth sacral vertebrae, the sacrotuberous ligament, and the superior margin of the sciatic notch. It exits the pelvis through the sciatic notch and inserts on the superior aspect of the greater trochanter at its posteromedial corner.

The function of the piriformis changes depending on the position of the hip. In extension, the piriformis externally rotates the hip, whereas in flexion, it becomes an abductor.

The sciatic nerve arises from the lumbosacral plexus and includes fibers from the L4-S1 nerve roots. Distally, it divides to form the tibial and perineal nerves. As the sciatic nerve exits the sciatic notch, it lies below piriformis muscle.

Numerous variations of the anatomy in this region have been described:

• An undivided sciatic nerve passing below the piriformis muscle (commonest)
• a divided sciatic nerve passing through and below the piriformis muscle
• a divided sciatic nerve passing above and below the piriformis muscle
• an undivided sciatic nerve passing through the piriformis muscle
• a divided sciatic nerve passing through and above the piriformis muscle
• an undivided sciatic nerve passing above the piriformis muscle

Sitting for prolonged periods of time is typically uncomfortable and becomes increasingly intolerable. Patient characteristically describe posterior hip and buttock pain and a variable pattern of radicular symptoms. These distal symptoms may be ill defined but follow the pattern of the sciatic distribution. These sensations may range from numbness and paresthesias to just a cramping sensation.

Numerous examination maneuvers have been described to assess for piriformis syndrome. No single finding is reliable in all cases, but a careful systematic examination should provide a reasonable clinical picture.

• Posterior pain is nonspecific. The overlying gluteus maximus and other closely related soft-tissue structures can be painful to palpation. Palpation for the piriformis should be localized directly posterior to the hip joint, close to the sciatic notch. Focal palpation may also recreate some of the patient’s radicular symptoms.
• Positive straight leg raising test is more likely to be indicative of lumbar nerve root irritation. Typically, straight-leg raise may produce localized posterior hip discomfort, but this is often nonspecific for a variety of conditions.
• Freiberg sign: With the hip extended, passive internal rotation and resisted external rotation of the leg are both maneuvers that may reproduce pain around the area of the piriformis
• Pace sign: In flexion, the piriformis becomes an abductor, so resisted abduction of the flexed hip is another provocative test
• Piriformis stretch: At 90° of flexion passive adduction and internal rotation can produce symptoms.

There are no specific radiographic features associated with piriformis syndrome, but imagining may help to rule out other radiographically identifiable processes. For recalcitrant cases MRI of the pelvis is prudent to rule out a mass effect within the sciatic notch or intrapelvic lesions. MRI of the lumbar spine is also important to rule out lumbar nerve root pathology.

EMG studies may help to rule out other causes of pain. It is rare that piriformis syndrome will result in measurable electromyogram or conduction deficits. If abnormalities are noted, there should be selective preservation of the superior gluteal nerve, which exits the notch above the piriformis muscle. A prolonged H:-reflex latency may be indicative of piriformis syndrome and this finding is accentuated if the hip is placed in a position of flexion, abduction, and internal rotation (Fishman et al).

Injection of local anaesthetic and steroids can be effective in management of piriformis syndrome. Because of its deep location and relation to adjacent neurovascular structures, the piriformis injection is best performed under imaging guidance, ideally ultrasound.

Diagnostic

Piriformis injection is also an important diagnostic tool. If relief is obtained even on a temporary basis, it helps to substantiate the diagnosis of piriformis syndrome.

Therapeutic

Injection of local anaesthetic and steroid in to the piriformis muscle can be therapeutic and help resolve the pain on a long-term basis.

There are limited studies for botulinum toxin A injections for piriformis syndrome; however, Childers and colleagues showed analgesic benefit from botulinum toxin A injections into the piriformis under guidance.

Botulinum toxin A has been shown to act at the level of the muscle spindle by inhibiting gamma motor neurons and blocking type Ia afferent signals, thus affecting both motor and sensory pathways. Botulinum toxin A may derive some of its analgesic effect by inhibiting the release of substance P from nerve terminals.

Injections are generally avoided in patients with systemic infection or skin infection over puncture site, bleeding disorders or coagulopathy, allergy to local anaesthetics or any of the medications to be administered. Injections are also generally contraindicated in pregnancy.

The procedure is usually done on an outpatient basis. Piriformis injection is performed under ultrasound guidance to ensure accuracy of needle placement. Patients need to be aware that the outcome of the procedure is variable and they may not receive the desired benefits. Similarly, they must be aware of the transient nature of the therapeutic benefits and that there may need repeated injections.

Generally a mixture of local anaesthetic and steroid is injected. The local anaesthetic agent within the injectate may act on the nociceptive fibres , whereas corticosteroids may reduce inflammation. The anaesthetic is probably responsible for immediate pain relief, whereas steroids are believed to be responsible for pain relief 2–6 days after their administration.

Complications are rare, particularly if the injections are performed using a precise needle-positioning technique. Possible complications include bruising, infection, hematoma, nerve injury and reaction to the injectates. Infection can be avoided with appropriate aseptic precautions. Severe allergic reactions to local anaesthetics are uncommon. Steroid injections may produce local reactions, occurring most often immediately after injection. These local reactions last for 24 to 48 hours, and are relieved by application of ice packs. Post-procedural pain flare-up may occasionally occur, and may be treated with painkillers. Neurological complications (injury to sciatic nerve) including paraesthesias and numbness have been described but are rare.

For exercises for management of pirioformis pain, please click the link below:

Exercises for Management of Piriformis pain