The posterior elbow triangle is the triangle enclosed by the medial epicondyle and lateral epicondyle of the humerus and the tip of the ulnar eminence. Generally, when the elbow is flexed at 90 degrees, the three points are in the shape of an isosceles triangle, and when the elbow is fully extended the three points are in a straight line. If there is a dislocation or fracture of the elbow joint, the posterior elbow triangle will be lost. The relationship of the posterior elbow triangle can be used to determine whether there is a dislocation or serious fracture of the elbow joint, or whether there is an obvious fracture or dislocation by local x-ray. If the initial examination reveals that the posterior elbow triangle is abnormal, further posterior elbow triangle examination should be performed gently and avoid excessive movements, as this may cause secondary injuries.