Summarize:

Research indicates that women are six times more likely to have piriformis syndrome than men. Piriformis syndrome occurs most commonly in people between ages 30 and 50. The higher rate of diagnosis among women may be explained by the difference in biomechanics in men's and women's pelvises. Women may also develop piriformis syndrome during pregnancy. Because the pelvis widens during pregnancy, it can cause the attached muscles to contract. Pregnant women also often develop a pelvic tilt to accommodate the baby's weight, which can also lead the attached muscles to become tight. You may be more likely to be diagnosed with piriformis syndrome if you have certain other medical conditions, such as low back pain. About 15% of cases are due to a congenital or structural anomaly concerning the relationship between the piriformis muscle and the sciatic nerve. The majority of cases of piriformis syndrome are caused by what doctors call "macrotraumas" or "microtraumas." A macrotrauma is caused by a significant traumatic event, such as a fall or a car accident. Macro-trauma to the buttocks, which leads to inflammation of the soft tissue, muscle spasms, and nerve compression, is a common cause of piriformis syndrome. A microtrauma is a pattern of repeated minor injury to an area. For example, long-distance runners expose their legs to constant micro-trauma, which can eventually cause nerve inflammation and muscle spasm. Running, walking, climbing stairs, or even sitting for long periods of time can cause your piriformis muscle to compress and entrap the sciatic nerve, causing pain. Another form of microtrauma that may cause piriformis syndrome is "wallet neuritis." This condition can occur when a person carries a wallet (or cellphone) in his back pocket, which can press against the sciatic nerve, causing irritation.
Consider your sex and age. Evaluate your health. Consider your activities.