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Piriformis syndrome occurs most frequently between ages 40-60 and is more common in women than men. Some reports suggest a 6:1 female-to-male ratio for piriformis syndrome; , possibly because of biomechanics associated with the wider quadriceps femoris muscle angle (ie, “Q angle”) in the pelvis of women. Reported incidence rates for piriformis syndrome among patients with low back pain vary widely, from 5% to 36%.
The most common symptom of patients with piriformis syndrome is increasing pain after sitting for longer than 15 to 20 minutes. Many patients complain of pain over the piriformis muscle (ie, in the buttocks), especially over the muscle’s attachments at the sacrum and medial greater trochanter. Symptoms, which may be of sudden or gradual onset, are usually associated with spasm of the piriformis muscle or compression of the sciatic nerve; these symptoms include radiating/shooting pain or tingling or numbness in the back of the thigh, leg, or foot. These symptoms must be evaluated by a healthcare provider to differentiate the possible causes. Patients may also complain of difficulty walking and of pain with internal rotation of the involved leg, such as occurs during cross-legged sitting or walking. X-rays or an MRI offer little help in directly diagnosing piriformis syndrome but may be used to rule out other causes of sciatica such as a herniated disc in the lumbar spine.
There are many functional abnormalities that may have either caused or resulted from this condition. Once the diagnosis has been made, these underlying, perpetuating biomechanical factors must be addressed.
Functional biomechanical deficits associated with piriformis syndrome may include the following:
- Tight hip external rotators including pirifromis
- Tight adductors (groin)
- Hip abductor weakness
- Lower lumbar spine dysfunction
- Sacroiliac joint hypomobility
- Hyperpronation of the foot and prolonged toe-off
Functional adaptations to these deficits include the following:
- Ambulation with the thigh in external rotation
- Functional limb length shortening
- Shortened stride length
Next post will discuss treatment options for piriformis syndrome
Piriformis syndrome is a unique cause if sciatic nerve irritation (neuritis) or sciatica. The condition, which can mimic lumbar disc herniation, usually is caused by irritation of the sciatic nerve due to spasm and/or contracture of the piriformis muscle. Piriformis syndrome is also referred to as “pseudosciatica”, “wallet sciatica”, and “hip socket neuropathy”.
It frequently goes unrecognized or is misdiagnosed in clinical settings. Piriformis syndrome can “masquerade” as other common somatic dysfunctions, such as intervertebral discitis, lumbar radiculopathy, primary sacral dysfunction, sacroiliitis, sciatica, and trochanteric bursitis.
The proper understanding of piriformis syndrome requires knowledge of the anatomy and anatomical variations in the relationships between the sciatic nerve and the piriformis muscle.
The piriformis muscle is flat, pyramid-shaped, and oblique. This muscle originates on the front of the sacrum and inserts at the greater trochanter of the femur. With the hip extended, the piriformis muscle is an external rotator of the hip; however, with the hip flexed, the muscle becomes a hip abductor.
In most of the population, the sciatic nerve exits the pelvis deep along the lower surface of the piriformis muscle. However, many developmental variations of the relationship between the sciatic nerve in the pelvis and piriformis muscle have been observed. In as much as 22% of the population, the sciatic nerve pierces the piriformis muscle, splits the piriformis muscle, or both, predisposing these individuals to irritation of the sciatic nerve.
Causes of Piriformis Syndrome
Piriformis syndrome can be caused by a variety of issues. The underlying mechanism is from irritation to the sciatic nerve. Below are some causes of irritation to the sciatic nerve as it passes the piriformis muscle:
1. Muscular problems
- Spasms and adhesions in the piriformis muscle cause compression and irritation of the sciatic nerve. Muscular damage or tightness can develop from a single injury or repetitive use injury. Vigorous physical activity can lead to such an injury- (commonly seen in athletes such as runners, cyclists, and dancers).
- Hyperlordosis (increased curvature of the low back) and increased foot pronation are both risk factors for piriformis syndrome
- Direct compression of the piriformis and/or sciatic nerve from an external soure such as a wallet.
4. Partial or total nerve anatomical abnormalities
- An anomaly in the nerve itself as it passes through the piriformis muscle can lead to dysfunction
5. Other causes can include the following:
- Pseudoaneurysms of the inferior gluteal artery adjacent to the piriformis syndrome
- Bilateral piriformis syndrome due to prolonged sitting during an extended neurosurgical procedure
- Cerebral Palsy
- Total hip arthroplasty
- Myositis ossificans