Femoroacetabular impingement (FAI), also referred to as hip impingement, occurs when an extra bone grows alongside one or both of the bones that structure the hip joint. FAI causes the bones to take on an irregular shape and grind against each other during movement.

This friction between the bones can damage the joint, leading to a decreased range of motion in the hip and feelings of pain and stiffness in the groin area or near to the outside of the hip.