MODEL RELEASED. Hip replacement surgery. Image 4 of 9. Prosthetic hip socket cup (white, centre) being tried for size during hip replacement surgery. The socket of the hip joint (with screws) has been strengthened and remodelled with part of the removed femur (thigh bone) head. Joints may need to be replaced after injury, disease or deformity. This hip is being replaced because of congenital hip dysplasia, a condition where the hip joint does not fit together properly, causing it to dislocate frequently and to become worn. For a sequence showing the operation see M551/418- M551/426.