Arthritic hip. Coloured X-ray of the pelvis of a 62-year-old patient, showing arthritis of the left hip joint (lower right). The pelvis (butterfly- shaped bone structure) joins to the lower backbone (white, upper centre). The tops of the two upper leg bones (femurs) are at lower right and left. The femoral heads (round) fit in sockets in the pelvis. The right femoral head (lower left) is smooth, and fits neatly into its socket. The left femoral head (lower right) is rough and pitted (white), showing that the friction-reducing joint cartilage has worn away. The joint will be stiff and painful and may require replacement.