Piriformis syndrome,many patients got this diagnosis,but it really exists? No one know.....

It is thought that the piriformis muscle tendon may be tethering the sciatic nerve, and causing an irritation to the nerve. While it has not be proven, the theory supported by some physicians is that when the piriformis muscle and its tendon are too tight, the sciatic nerve is choked. This may decrease the blood flow to the nerve and irritate the nerve because of pressure. (Quote from http://orthopedics.about.com)

According to zak acupuncture experiences,So call piriformis syndrome,its real reason is soft tissue injuries in buttock and lower back area,So,The treatment that patients have surgery to release, or loosen, the piriformis muscle tendon is possibly not wise idea.Deep and intensive acupuncture can help most of cases.Zak claim.
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Chinese patients were treated by acupuncture at Huantiao (GB 30), Yanglingquan (GB 34) and Shenmai (BL 62), with needling shallow, middle and deep layers for Huantiao, Yanglingquan, and after acupuncture massage was given at the Foot-Taiyang Channel and the Foot-Shaoyang Channel on lumbosacral region and the affected foot.
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Reference:Zhongguo Zhen Jiu. 2008 Mar;28(3):205-6