The iliopsoas muscle is a term that refers to a group of three muscles of the hip, the psoas major, the psoas minor, and the iliacus. In about half of the population, the psoas minor is not present as an anatomically distinct muscle. The two or three muscles of the iliopsoas group tend to be easily distinguishable in the abdomen region, where they originate, and in most cases they merge into a relatively indistinguishable mass in the thigh, where they attach to the leg. The iliopsoas muscle group is used in walking and running, and in maintaining posture while standing.
The origin of the psoas major, and the psoas minor if it is present, is along the side of the lower vertebrae of the spine. The iliacus muscle originates on the hipbone, or pelvis, where it is attached to a structure called the iliac fossa, a large hollow on the inside of the ilium, one of the three fused bones that make up the pelvis. The iliopsoas muscle group comes together around the top of the pelvis, and from there traverse the joint of the hip. They insert at the top of the leg, where they are attached to the upper leg bone, the femur, at a location called the lesser trochanter, a relatively small bony protuberance at the upper end of the femur, near the hip.
Iliopsoas muscle pain can be caused by inflammation, stretching, or tearing of the iliopsoas muscles or tendons. Where the cause of hip pain is inflammation, the condition is usually termed iliopsoas tendinitis. Iliopsoas syndrome, on the other hand, is the term that is usually employed to refer to physical damage, such as tearing, of the muscles or tendons of the iliopsoas. In severe injuries, one of the muscles of the iliopsoas group may even rupture.
Injuries are most often experienced in the region of the muscle at or near the point where it attaches to the femur, rather than at the site of origin of the muscles in the abdomen. Inflammation may result from overuse of the muscles, as may occur, for example, during intensive running or jumping. Other activities that carry a high risk of iliopsoas muscle strain include sports where a lot of kicking is performed, and weight training exercises that involve squatting and bending. Physical damage may occur if the iliopsoas muscle is contracted quickly when an athlete has not warmed up sufficiently.