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 right. Palpation detects diminished excursion of the articular head in the left lower jaw. Mouth opening is reduced to 1 cm. Make the preliminary diagnosis: