Hip is the region of the body between the trunk and the thigh. The hip joint is formed by the hipbone—which consists of three united bones, the ilium, ischium, and pubis—and the head of the femur (thighbone). The head of the femur fits into the acetabulum, a socket in the hipbone. This arrangement forms a ball-and-socket joint, which provides great strength and allows a wide range of motion in all directions. Several powerful muscles surround the joint. These muscles make the joint firm so a person can stand. They also move the leg for walking and running.
Many children are born with a hip socket that is too shallow and bones that are not aligned properly. This condition is called congenital dislocation of the hip. In old age, the neck of the femur, located just below the head of the femur, becomes weak and breaks easily. The break can be repaired by fastening the head on the neck with a stainless steel nail or by replacing the head with a metal ball. Many arthritis victims suffer disabling pain in the hip joint. In such cases, the joint can be replaced by a plastic socket and a metal ball.
