A patient has a negative stress test for the medial collateral ligament and radiographs show the coronoid process inferior to the trochlea. Which elbow displacement is most likely?

• A. Varus displacement
• B. Valgus displacement
• C. Anterior displacement
• D. Posterolateral displacement

Answer: (D)

Elbow dislocations are understood by how the ulna moves relative to the distal humerus. If the medial collateral ligament test is negative, valgus (medial) instability is unlikely, so a valgus-directed injury isn’t the best fit. The radiograph finding that the coronoid process is inferior to the trochlea points to the ulna having shifted backward relative to the humerus. When the ulna moves posteriorly and outward, the typical pattern is posterolateral dislocation. That combination—no medial (valgus) laxity and a radiographic sign showing backward, lateral displacement of the ulna—best explains a posterolateral elbow dislocation.