Accurate elbow x ray interpretation is a fundamental skill for emergency physicians, radiologists, orthopedic surgeons, and advanced practice providers. The elbow joint contains multiple closely apposed bones, and subtle displacement can be easily missed without a structured approach. A systematic evaluation reduces the risk of missing a fracture, dislocation, or associated soft tissue injury.
Essential Anatomy and Joint Spaces
Before interpreting the study, a clear understanding of the normal anatomy is non-negotiable. The three main bones forming the joint are the humerus, radius, and ulna. Proper assessment requires evaluating several key joint spaces and bony landmarks on both anteroposterior (AP) and lateral views.
On the AP view, the radial head should be centered within the capitellum, maintaining a symmetric joint line. The trochlear groove of the distal humerus should be smooth and symmetric. On the lateral view, the anterior humeral line, drawn along the anterior humeral cortex, should intersect the middle third of the capitellum in a normal elbow. The radiocapitellar joint space should appear congruent, indicating proper alignment of the radius and capitellum.
Applying the Ottawa Ankle Rules to the Elbow
Clinical decision rules help determine which injured patients truly require imaging to avoid unnecessary radiation. While the Ottawa Ankle Rules target the foot, parallel validated criteria exist for the elbow to guide initial x ray ordering. These rules are highly sensitive for detecting significant fractures in the acute setting.
Posterior elbow tenderness at the distal humerus.
Inability to flex the elbow to 90 degrees.
Inability to supinate the forearm.
Tenderness at the radial head or neck.
Fulfillment of any one of these criteria generally indicates the need for radiography to rule out fracture.
Identifying Common Elbow Fractures
Recognizing the patterns of common fractures is essential for accurate diagnosis. These injuries often result from falls onto an outstretched hand (FOOSH) and can vary in complexity. A meticulous review of the x ray should focus on the cortex continuity and trabecular alignment.
Radial Head Fractures: These are among the most frequent elbow injuries. Look for a joint effusion (sail sign) on the lateral view or a displaced fragment on the AP view. Non-displaced fractures may only reveal subtle cortical irregularities.
Olecranon Fractures: The olecranon acts as the anchor for the triceps tendon. A fracture here often disrupts the smooth posterior humeral line. Displacement occurs when the triceps force pulls the fragment proximally.
Distal Humerus Fractures: These include supracondylar fractures, common in children, and intercondylar fractures in adults. A supracondylar fracture typically shows a posterior displacement of the distal fragment, creating a characteristic "posterior fat pad" or "sail sign" due to anterior joint effusion.
Assessing Joint Alignment and Dislocations
Beyond fractures, the x ray must evaluate the integrity of the joint surfaces and the stability of the articulation. Dislocations are dramatic injuries that require prompt reduction, but associated fractures are a significant concern.
When evaluating the lateral view, the relationship between the radius and the capitellum is critical. A radial head dislocation is seen in combination with a coronoid fracture, indicating a terrible triad injury. The alignment of the trochlea and the carrying angle should also be noted, as malalignment can indicate a missed fracture or ligamentous injury.
