Final answer:
For a lateral elbow x-ray, the elbow must be flexed 90 degrees to provide a clear view of the joint's structures, ensuring accurate diagnosis or surgical planning, by clearly depicting the humeroulnar and humeroradial joints, and providing essential ligament visibility.
Step-by-step explanation:
The elbow view for a lateral elbow x-ray requires the elbow to be flexed 90 degrees to ensure an accurate representation of the joint's structures. At 90 degrees of flexion, the humerus and forearm bones, the radius and ulna, are positioned in a way that the X-ray can clearly show the joint space and the adjacent bony landmarks without overlaying structures obscuring the view. This position allows for optimal visualization of the elbow joint, the ulnar collateral ligament, the radial collateral ligament, and the annular ligament, which together stabilize the elbow and prevent hyperextension. The orientation also demonstrates the carrying angle and ensures a clear depiction of the proximal radioulnar joint where the radius and ulna articulate, providing essential information for diagnosis or preoperative planning.