A patient sustains a fracture through the ANGLE of the mandible. In which direction will the posterior (proximal) fragment tend to be displaced?

Correct answer: A. Upward and medially, by the elevator muscles

• A. CORRECT. At the angle, the fracture line separates the mandible into a posterior (proximal) fragment carrying the muscles of ELEVATION — masseter laterally, medial pterygoid medially, temporalis on the coronoid — and an anterior fragment carrying the DEPRESSORS (digastric, geniohyoid, mylohyoid). The unopposed elevators pull the proximal fragment UPWARD and MEDIALLY, producing a step deformity, deranged occlusion and premature contact on the fractured side.
• B. Displacement at the angle is common and clinically significant. Whether a fracture is FAVOURABLE or UNFAVOURABLE depends on whether the fracture line direction resists or permits muscle-driven displacement.
• C. Gravity is trivial compared with the muscle pull. The direction of displacement in any mandibular fracture is determined by which muscle groups act on which fragment.
• D. The lateral pterygoid protrudes the mandible and is the dominant displacing force in CONDYLAR fractures, not angle fractures.

Note: Favourable vs unfavourable is the concept being tested: a fracture line running such that the muscle pull draws the fragments TOGETHER is favourable and may be treated with closed reduction; one that pulls them APART is unfavourable and needs open reduction and internal fixation.