They can’t. Joints are held in place by ligaments, muscles and fossa to ensure they move within a certain range. A prolapse will cause damage to the ligaments and muscles, which is generally irreversible and difficult to repair due to constant movement, making it difficult for the joint to maintain its original function. It is difficult to repair because of the constant movement and it is difficult to maintain the original function of the joint. At present it is more likely to be removed to reduce friction and allow the muscles to form a pseudo-joint to maintain movement. It is also possible to try to return to a normal position (which requires professional manipulation) and rest to see if it will prolapse again before considering surgery.
