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Sciatic pain reproduced on passive internal rotation/adduction of a flexed hip is considered suggestive of the syndrome. Typically, no neurological deficit will be elicited on examination as well as a negative straight leg raise test 7.
The general, although by no means unanimous consensus is that piriformis syndrome is caused when hypertrophy, inflammation, injury or anatomical variation of the piriformis muscle results in compression of the sciatic nerve as they both exit the pelvis through the greater sciatic notch.
Normally, the sciatic nerve typically passes immediately anterior to the piriformis muscle. This relationship is variable, however, as the nerve occasionally passes through the muscle, or splits early, with part of it passing through the muscle.
Additionally, an accessory piriformis muscle that arises from the more medial part of the sacrum can be implicated.
early sciatic nerve division and passage through the muscle belly or above it
narrowed sciatic foramen
ganglion or cyst
any mass lesion
bursitis and inflammation
MRI is the only modality that can adequately visualize the region. The radiographic appearance depends on the cause, and often no abnormality is noted. If muscle injury or inflammation is present then increased signal within the piriformis muscle may be seen on T2 MRI. An accessory piriformis muscle may be identified.
Treatment and prognosis
physiotherapy with stretching (especially if a spasm is thought to be the cause)
administration of non-steroidal anti-inflammatory agents
injection of local anesthetic and steroid
injection of botulinum toxin to atrophy the piriformis muscle
surgical release of the piriformis muscle
History and etymology
Entrapment of the sciatic nerve by the piriformis muscle was first described By W Yeoman in 1928 1.
Clinically it should be distinguished from hamstring syndrome.
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