Hip replacement surgery. Image 25 of 30. New hip socket (white) in place in the pelvis. The socket will articulate with the ball of an implant placed in the femur (upper leg bone). Together, these two implants will form the new hip joint. This surgery is usually performed in response to arthritis, the degeneration of the joints, and restores mobility to people who would otherwise be incapacitated by pain and unable to move freely. For a sequence of images showing the full surgery, see M551/340- 369. For a sequence showing the operation on the pelvis, see images M551/360-366.