Question: If passive flexion and passive extension of the elbow are painful and limited, what structure is injured?

Answer: The elbow joint.

The elbow joint is a complex structure located at the juncture of three separate bones: the humerus, the ulna and the radius. It's primarily a hinge joint, with portions of the joint able to pronate and supinate. The bone surfaces are held together by a joint capsule containing four thickened portions, which generally are described as separate ligaments: the ulnar collateral ligament, the radial collateral ligament, and the anterior and posterior ligaments of the elbow. Within the joint capsule lies the synovial membrane.

The elbow joint might be injured through a single trauma, such as a fall, or by repeated mini-traumas, such as using a hammer for several hours at a time. When this happens, synovial fluid is overproduced, and this limits the actions of the elbow. In addition, inflammation within the joint makes it painful to fully flex or fully extend the elbow. The person might feel pain when performing a variety of motions that cause stress to the joint, such as lifting, biking and prolonged typing.