Review Question - QID 217443

A 42-year-old male presents to the ED following a posterolateral elbow dislocation after a snowboarding accident. His elbow is reduced in the ED and post-reduction imaging reveals no fracture. Two weeks later, he complains of difficulty pushing up out of a chair. On examination, with the patient laying supine and the affected arm placed overhead, he reports pain and clunking when the forearm is supinated and a valgus stress is applied while bringing the elbow from full extension to 40 degrees of flexion. Which of the following ligaments in Figure A is the primary stabilizer to varus and external rotation stress of the elbow that is deficient in this patient?