The pyriformis muscle is deep in the buttocks and may trap the sciatic nerve in its course down the back of the leg. This is often made worse by prolonged sitting (e.g., working at a computer), strenuous twisting of the torso (e.g., shoveling snow), or even by falling on one’s backside (e.g., the pyriformis muscle goes into spasm). This may lead to lower backache, weakness of the hip (on the affected side), difficulty walking, pain down the back of the thigh, and numbness of the lower leg--in short, all the classic signs of a herniated disc....