Damage from an injury to the hip can create loose bodies of cartilage covered pieces of bone which float around the joint. These can jam and cause locking symptoms and severe pain.
Synovial chondromatosis is a condition where the lining of the joint is abnormal and makes small lumps of cartilage which can float around causing pain when they jam in the joint.
These can be removed arthroscopically and the synovitis treated.