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The ischiofemoral ligament is a band of connective tissue that helps contain the head of the femur bone in the hip joint. Broad at one end and tapered at the other to form a triangle, this ligament stretches between the ischium bone of the pelvis and the femur, the long bone of the thigh. Crossing the rear aspect of the hip joint, the ischiofemoral ligament limits the degree to which the leg can rotate medially, or internally, in the hip socket.
Where the femur meets the pelvis is the acetabulofemoral or hip joint, a ball-and-socket joint in which the head of the femur is contained within a rounded cavity on the pelvis known as the acetabulum. Holding the head of the femur in the acetabulum are ligaments surrounding it on all sides, connective tissue that not only prevents the femoral head from popping out of the joint, but also restricts the range of motion of the leg in the hip. The ischiofemoral ligament is among this tissue.
Arising from the ischium, the bone that is located on the lower posterior aspect of the pelvis, the ischiofemoral ligament extends laterally from immediately behind the hip socket. Its fibers begin high on the posterior ischium next to the acetabulum and are continuous along the entire back side of the joint until slightly below the acetabulum. In other words, this end of the ligament is broad, covering the back of the hip joint.
After crossing the joint, the fibers of the ischiofemoral ligament begin to taper, twisting forward over the neck of the femur. The neck is the portion of the top of the bone upon which the femoral head sits, and it angles inward and slightly upward off the main shaft of the bone at an approximate 125-degree angle. Several of the deeper fibers of this ligament mingle with those encircling the capsule of the hip joint. The rest attach to the line demarcating the border between the neck and shaft of the femur, the intertrochanteric line, which is found on the anterior side of the bone and is roughly parallel to the shaft.
Along with the iliofemoral ligament, which covers the front side of the hip joint, and the pubofemoral ligament, which covers the underside of the joint, the ischiofemoral ligament not only partially surrounds the hip joint but controls its range of motion. Studies of human cadavers have found that when this ligament is detached from the femur bone, the leg can be rotated medially to a much greater degree than it can when the ligament is present. In other words, the ischiofemoral limits internal rotation of the hip, and it does so whether the leg is flexed in front of the body, neutral, or extended behind the body.