The piriformis muscle is a small, pear-shaped muscle located deep in the buttock, behind the hip joint. It originates from the sacrum and attaches to the top of the femur. Its primary functions are to externally rotate the hip, assist with hip abduction when the hip is flexed, and stabilize the pelvis during walking and standing. Despite its small size, the piriformis plays a crucial role in lower-body movement and balance.

Piriformis syndrome occurs when this muscle becomes tight, inflamed, or spasms, leading to compression or irritation of the sciatic nerve. Because the sciatic nerve runs beneath — and in some individuals, through — the piriformis muscle, dysfunction can cause symptoms similar to sciatica. These symptoms typically include deep buttock pain, tenderness, and radiating pain, tingling, or numbness down the back of the thigh. Prolonged sitting, climbing stairs, or repetitive activities like running can aggravate the condition.