Failed hip joint replacement. Coloured X-ray of the pelvis (front view) of an 83 year old woman, showing two types of prosthetic (artificial) hip joint implants, one of which has failed. At right the implant has loosened and become displaced from its socket in the pelvic (hip) bone. The hip joint is a ball-and-socket joint. The ball part of the implant is attached by a long peg into each femur (thigh) bone with surgical cement. The socket of each joint, located in the pelvis bone, has also been replaced. However, one implant has pulled out of its socket, dislocating the leg, and this would require surgical correction. Hip prostheses are made of a composite metal alloy. A hip joint may need to be replaced because of disease such as arthritis, or due to injury.