Hip replacement was once impossible because, although joints could easily be produced in a laboratory, the human body rejected the materials. If a knee or hip joint breaks in an accident or wears out in old age, a surgeon can replace it with a ball-and-socket joint made from metal and plastic and engineered in such a way that it will duplicate the motions of a human joint. The hip joint must be able to accommodate these extreme forces repeatedly during intense physical activities. During running and jumping, for example, the force of the body’s movements multiplies the force on the hip joint to many times the force exerted by the body’s weight. In addition to being flexible, each hip joint must be capable of supporting half of the body’s weight along with any other forces acting upon the body. Only the shoulder joint provides as high of a level of mobility as the hip joint. The femur may also rotate around its axis about 90 degrees at the hip joint. The ball-and-socket structure of the joint allows the femur to circumduct freely through a 360-degree circle. The strong muscles of the hip region also help to hold the hip joint together and prevent dislocation.įunctionally, the hip joint enjoys a very high range of motion. Surrounding the hip joint are many tough ligaments that prevent the dislocation of the joint. Between the layers of hyaline cartilage, synovial membranes secrete watery synovial fluid to lubricate the joint capsule. Hyaline cartilage also acts as a flexible shock absorber to prevent the collision of the bones during movement. Hyaline cartilage lines both the acetabulum and the head of the femur, providing a smooth surface for the moving bones to glide past each other.