A sudden unlocking of the joint may be caused by a sudden change in pressure inside the joint, for example, if the joint is fixed in a certain position for a long time during a competitive sporting activity, 3. It may be caused by free bodies inside the joint, which refers to free, abnormal calcium salt deposits inside the joint due to joint injury and sterile inflammation. The deposited calcium salts may become sphere-like objects, which may lead to popping and jamming when the patient moves the joint.4. It may also be caused by tendon pathology, such as aseptic inflammation around the tendon or tendinitis, which may cause sudden sliding of the inflamed and enlarged part during joint movement, and then cause a sound.