Approach to ELBOW radiograph

1. Introduction and Standard Views

The elbow is a complex hinge and pivot joint, and subtle fractures or dislocations can be easily missed due to overlapping anatomy. A systematic approach, especially focusing on alignment and soft tissues, is paramount.

Standard Views:

• AP View: Best for assessing the distal humerus (condyles, epicondyles) and the proximal forearm (radial head, olecranon process). The carrying angle (humerus and forearm axis) is best seen here.

  
  

• Lateral View (90 degrees Flexion): The most crucial view for assessing alignment and detecting joint effusion via the fat pad signs. The lateral view clearly profiles the trochlea, olecranon, coronoid process, and radial head relationship.

  
  

• Oblique/Radial Head Views (Coyle's View): Often requested if a radial head fracture is suspected but not clearly seen on standard views, as it projects the radial head free of superimposition.

2. Soft Tissue Assessment: The Fat Pad Signs

The soft tissues often provide the only initial sign of an occult intra-articular fracture.

The Significance of the Fat Pads:

The elbow joint capsule contains extra-synovial fat pads that are normally hidden or only minimally visible. Any intra-articular fluid (hemarthrosis, pus) elevates and displaces these pads.

1. Anterior Fat Pad (Sail Sign):

   • Normally seen as a small, faint lucent stripe lying close to the anterior cortex of the distal humerus.

     
     

   • Abnormal: When lifted and displaced away from the bone, it forms a triangular silhouette resembling a billowing sail (Sail Sign).

     
     

2. Posterior Fat Pad:

   • Normally nestled deep within the olecranon fossa and never seen on a normal, true lateral radiograph.

   • Abnormal: Any visualization of the posterior fat pad is always pathological and indicates an elbow joint effusion.

Fat Pad sign	Significance	Fractures associated
Visible Posterior Fat Pad (ALWAYS Abnormal)	Joint Effusion (Hemarthrosis)	Adults: Radial Head Fracture
Raised Anterior Fat Pad (Sail Sign)	Joint Effusion (Hemarthrosis)	Children: Supracondylar Fracture

3. Bony Alignment (Lateral View)

Two key alignment lines must be drawn to check for subtle subluxation or fracture displacement.

A. Radio-capitellar Line (RCL)

• Definition: A line drawn through the center of the radial shaft and neck on both the lateral and AP views.

• Normal: This line must always bisect the capitellum in all views, regardless of the degree of elbow flexion.

  
  

• Abnormal: If the line does not pass through the capitellum, it indicates a radial head dislocation (or subluxation), which is often part of a complex injury like a Monteggia fracture-dislocation (proximal ulna fracture with radial head dislocation).

B. Anterior Humeral Line (AHL)

• Definition: A line drawn along the anterior cortex of the distal humerus on the lateral view.

  
  

• Normal: The line should pass through the middle third of the capitellum (ossification center).

  
  

• Abnormal: If the line passes entirely anterior to the capitellum, it strongly suggests a posterior displacement of the capitellum/forearm, most commonly due to a Supracondylar Fracture of the distal humerus (especially in children).

4. Bony Survey: Systematic Fracture Search

Trace the cortex of every bone meticulously, paying special attention to high-yield areas.

1. Radial Head & Neck:

   • Most common adult elbow fracture. Often non-displaced and only evident by the Fat Pad Sign. Look for subtle cortical jogs, step-offs, or lucency across the neck.

     
     

2. Distal Humerus:

   • Supracondylar: Most common fracture in children. Look for displacement based on the AHL.

     
     

   • Condylar/Epicondylar: Check the integrity of the medial and lateral epicondyles. A Medial Epicondyle fracture is often an avulsion injury and may be incarcerated within the joint after dislocation (requires careful search).

     
     

3. Olecranon Process:

   • Look for a transverse fracture line, often with distraction due to the pull of the triceps tendon. Assessed best on the Lateral View.

4. Coronoid Process:

   • A fracture here is a key component of the "Terrible Triad" (elbow dislocation + radial head fracture + coronoid fracture). Look for an avulsed fragment off the proximal anterior ulna on the lateral view.

     
     

Pediatric Considerations (CRITOE)

When reviewing a pediatric elbow, be familiar with the order of ossification center appearance to avoid confusing normal anatomy with a fracture:

C-R-I-T-O-E

Ossification Center	Approximate Age of Appearance
Capitellum	1 year
Radial Head	3 years
Internal (Medial) Epicondyle	5 years
Trochlea	7 years
Olecranon	9 years
External (Lateral) Epicondyle	11 years

A fracture should be suspected if an ossification center is present but out of order or if it is displaced/absent from its expected location (e.g., a displaced medial epicondyle).

5. Joint Space and Alignment

• Overall Alignment: Note any gross dislocation, usually posterior or posterolateral dislocation of the ulna/radius relative to the humerus.

• Joint Space: Check for uniform space between the trochlea/olecranon and the capitellum/radial head. Look for joint space narrowing in non-traumatic cases (arthritis).

• Loose Bodies: Inspect the joint space for osteochondral fragments or displaced epicondyle fragments.