Internal Derangement (Disc Dislocation)
- Derangement of the Joint System; a displaced disc
- Anterior Disc Displacement with Reduction (Clicking): A clicking or popping sound occurs as the disc returns to its normal position in relation to the condyle. During closure, the disc again becomes anteriorly displaced, sometimes accompanied by a second sound (reciprocal click).
- Anterior Disc Displacement without Reduction (ADDWR/Locking): A progression of Anterior Disc Displacement with reduction. The displaced disc acts as a barrier and prevents full translation of the condyle. Only rotation occurs.
- Etiology: The three main causes of internal derangement of the intra-articular disc are: (1) trauma, (2) abnormal functional loading of the joint and (3) degenerative joint disease. Acute macrotrauma is the most common cause of internal derangement (blow to the jaw, intubation, stretching of the joint during dental procedures).