Piriformis syndrome is a type of neurological injury that is caused by compression of the sciatic nerve. The piriformis muscle sits deep within the buttock, behind the gluteus maximus. It starts at the lower spine and connects to the femur muscle. This nerve can become compressed from swelling of the piriformis muscle due to injury or muscle spasms or inflammation. Piriformis syndrome causes symptoms including pain in the back of the thigh, pain in the back of knee, buttock pain, pain in the calf, pain in sciatic nerve branches (pain in the nerves of leg and the buttocks, then), shooting pain in the legs, and hip pain after sitting.
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You can strain or tear one or more of your hip flexors when you make sudden movements such as changing directions while running or kicking. Sports and athletic activities where this is likely to occur include running, football, soccer, martial arts, dancing, and hockey. In everyday life, you can strain a hip flexor when you slip and fall, for example.