Stage IV disease involves displacement of the disc from the medial pole of the condylar head. Once again, there is a clicking phase and a locking phase in Stage IV. The clicking phase of Stage IV is called Stage IVa. Hence, this type of click occurs because the disc is displaced at the medial pole. In addition, there is laxity of the medial collateral ligament. Typically, these patients also have displacement of the disc from the lateral pole. It is a very unusual scenario for a patient to have displacement only from the medial pole without also having displacement from the lateral pole. These patients are more likely to develop intra-articular pain because both translatory as well as rotatory movement will be loading retrodiscal attachment. Appliance therapy for these patients can be successful in aligning the disc to a more normal position over the medial pole. In this scenario, so long as the medial part of the disc is reduced, even if they don't go all the way back to a Stage I, they may have fewer symptoms. Hence, the minimal goal with appliance therapy for a patient in Stage IV is to try to convert them to a Stage III. Over time, the more fibrosis of the lateral pterygoid muscle, the more discal deformity, and the more redundancy of the retrodiscal attachment, there is less likelihood that these patients will be able to revert to an earlier stage. In fact, if these processes progress in these patients, then they may develop a locking stage.