A 21-year-old man complains of difficult mouth opening and visible facial deformation throughout the last 2 years. He has a history of facial trauma several years ago. Examination shows the right side of the face to be flattened, the chin is displaced to the left. Palpation detects diminished excursion of the articular head in the left lower jaw. The mouth opening is reduced to 1 cm. Make the provisional diagnosis: