Early (proximal) divisions of the sciatic nerve into its tibial and common peroneal components can predispose patients to piriformis syndrome, with these branches passing through and below the piriformis muscle or above and below the muscle.AcquiredSitting for prolonged periods (office workers, taxi drivers, bicycle riders)Overuse syndromes: Piriformis muscle hypertrophy (viz., in athletes)Trauma to the hip or buttock area

Pathophysiology
When the piriformis muscle shortens or spasms due to trauma or overuse, it can compress or strangle the sciatic nerve beneath the muscle. Generally, conditions of this type are referred to as nerve entrapment or as entrapment neuropathies; the particular condition known as piriformis syndrome refers to sciatica symptoms not originating from spinal roots and/or spinal disc compression, but involving the overlying piriformis muscle.In 17% of an assumed normal population the sciatic nerve passes through the piriformis muscle, rather than underneath it; however, in patients undergoing surgery for suspected piriformis syndrome such an anomaly was found only 16.2% of the time leading to doubt about the importance of the anomaly as a factor in piriformis syndrome. Some researchers discount the importance of this relationship in the etiology of the syndrome.MRI findings have shown that both hypertrophy (unusual largeness) and atrophy (unusual smallness) of the piriformis muscle correlate with the supposed condition.Piriformis syndrome may also be associated with direct trauma to the piriformis muscle, such as in a fall or from a knife wound. Diagnosis
Piriformis syndrome occurs when the sciatic nerve is compressed or pinched by the piriformis muscle of the hip.
Sitting down on a thick Wallet in the back pocket produces uneven pressure in the hip region that impinges on the Piriformis muscle and / or sciatic nerve. Wallet induced chronic sciatic nerve constriction produces gluteal and ipsilateral lower extremity pain, tingling, and burning sensation.Diagnostic modalities such as ultrasound Imaging, MRI, CT scan, and EMG are mostly useful in excluding other conditions. Increased thickness [iTh] and increased cross‐sectional area [iCSA] for piriformis muscle may be demonstrated on ultrasound imaging and MRI.Magnetic resonance neurography is a medical imaging technique that can show the presence of irritation of the sciatic nerve at the level of the sciatic notch where the nerve passes under the piriformis muscle. However, Magnetic resonance neurography is considered "investigational/not medically necessary" by some insurance companies. Neurography can determine whether or not a patient has a split sciatic nerve or a split piriformis muscle – this may be important in getting a good result from injections or surgery. Image guided injections carried out in an open MRI scanner, or other 3D image guidance can accurately relax the piriformis muscle to test the diagnosis. Other injection methods such as blind injection, fluoroscopic guided injection, ultrasound, or EMG guidance can work but are not as reliable and have other drawbacks. Prevention
The most common etiology of piriformis syndrome is that resulting from a specific previous injury due to trauma. Large injuries include trauma to the buttocks while "micro traumas" result from small repeated bouts of stress on the piriformis muscle itself.