Double hip replacement. Coloured X-ray of a female patient's hips with two prosthetic hip implants (white). Each implant is embedded in a hole drilled into its femur (thigh bone, lower left and right). The head of each femur has been removed and each femur's articulation (joint) with the pelvis (upper centre) has been replaced by the head of its implant (round). Each head rotates in an artificial socket (dark brown) that has been fitted in each old pelvic hip socket. This mimics the old ball-and-socket joint, which is often replaced due to arthritis or severe injury, and restores much of the mobility that was lost.