The hip joint functions like a simple ball and socket joint. In a normal hip, the ball and socket are smooth, allowing a full range of pain free movement. In arthritis the ball and socket become rough and ragged, restricting range of movement and giving pain.
The Pre-Operative x-ray shows both hips of a patient. One hip is arthritic, whereas in the other hip the ball and socket are still smooth.
The Post-Operative x-ray shows a total hip replacement. Both the ball and socket have been replaced.