9.2 Elbow & Humerus

9.2 Elbow & Humerus

Quick Answer: The elbow series is built on AP (extended, hand supinated), medial and lateral 45° obliques, and a true lateral at 90° flexion. The lateral oblique shows the radial head/neck/tuberosity free of the ulna; the medial oblique shows the coronoid and trochlea. When extension is impossible, use partial AP projections or acute-flexion (Jones) views. Fat pads on the lateral elbow are soft-tissue alarms—especially a visible posterior fat pad. The humerus needs AP and lateral including both joints, with transthoracic lateral as a trauma alternative.

Elbow and humerus imaging sits at the junction of upper-extremity positioning skill and trauma problem-solving. CAMRT items love stems where the patient “cannot straighten the arm” or where the only abnormality is a raised sail-shaped anterior fat pad—testing whether you understand both projection selection and image analysis.

Elbow Anatomy Landmarks for Positioning

Know these surface and radiographic landmarks so CR placement and rotation critiques are automatic:

• Humeral epicondyles — rotation indicators for AP and lateral.
• Radial head, neck, tuberosity — free of superimposition on lateral oblique / Coyle radial-head view.
• Coronoid process — profiled on medial oblique.
• Olecranon process — in profile on lateral; seated in olecranon fossa on AP if fully extended.
• Trochlea and capitulum — form the distal humeral articular surfaces; concentric-arc relationships on lateral.

Routine Elbow Projections

Why 90° flexion on the lateral?

Ninety degrees separates the olecranon from the distal humerus optimally for most adults and standardizes fat-pad appearance. Hyperflexion or incomplete flexion changes relationships and can hide or fake soft-tissue signs. Rest the entire arm on the same plane—dropping the shoulder or elevating the hand rotates the humerus and destroys epicondylar superimposition.

Radial head laterals (Coyle method)

When the clinical question is radial head fracture and the patient cannot tolerate full external oblique, or when extra radial-head detail is ordered:

These horizontal or angled laterals are high-yield “special projection” knowledge for application items.

Acute flexion (Jones) projections

If the patient cannot extend the elbow at all (acute injury, cast, severe effusion):

• Distal humerus acute flexion: CR perpendicular to the humerus, directed between the epicondyles through the flexed joint region (demonstrate distal humerus and epicondyles).
• Proximal forearm acute flexion: CR perpendicular to the flexed forearm, demonstrating proximal radius/ulna.

Two images replace the single AP when one plane of the joint cannot be opened by extension. Label clearly so the radiologist knows which bone the CR was perpendicular to.

Fat Pad Signs (Lateral Elbow)

Technique note: Under-exposure or incorrect lateral rotation can obscure fat pads. Overly bright soft-tissue windows on digital review still require that the projection was a true lateral; you cannot “window in” anatomy that was never projected correctly.

Humerus

Erect positioning is preferred for comfort and to demonstrate air–fluid levels if relevant soft-tissue questions arise, but trauma patients may remain supine.

Trauma adaptations

Never abduct or rotate a severely injured arm just to “get the textbook lateral.” Options include:

• Horizontal-beam lateral of the distal humerus/elbow with the IR between the arm and thorax or alongside the arm.
• Transthoracic lateral humerus (Lawrence): Patient erect or supine; injured arm at side; unaffected arm raised over the head; CR through the thorax to the surgical neck of the affected humerus. Breathing technique (low mA, long exposure) blurs lung markings if the patient can cooperate. Use when proximal/mid-humeral fracture prevents rotation and a scapular-Y or axillary shoulder projection is not the ordered exam.
• Include the joint closest to the injury on every image; if the entire humerus cannot fit, obtain separate proximal and distal images with overlap rather than clipping the fracture margins.

Common Elbow & Humerus Injuries (Critique Context)

• Radial head/neck fractures — most common adult elbow fracture; look for positive fat pads and use lateral oblique or Coyle views.
• Supracondylar fractures — pediatric classic; anterior humeral line on lateral should intersect the middle third of the capitulum—know that departments assess this on a true lateral.
• Olecranon fractures — best on lateral; may need careful AP with limited extension.
• Proximal humerus surgical-neck fractures — common in older adults; AP + trauma lateral / transthoracic / scapular Y depending on protocol and what can be moved safely.

Technique Tips

Elbow and humerus straddle thin and thick part thicknesses. Manual technique charts should step kVp/mAs appropriately; grids may be used for larger humeri or transthoracic projections. Collimate tightly on the elbow to improve contrast of fat pads; open collimation on the humerus enough to include both joints without irradiating the whole chest unnecessarily—especially important on transthoracic laterals (shield and collimate to the humeral region of interest).

CAMRT Application Focus

Map stems to actions:

• “Cannot extend the elbow” → do not force AP extension; use acute-flexion Jones pair or partial flexion APs as protocol allows; still obtain a quality lateral if possible.
• “Query radial head fracture, standard AP looks normal” → check lateral fat pads; add external oblique or Coyle radial-head view.
• “Lateral elbow with visible posterior fat pad, no obvious fracture line” → treat as abnormal intra-articular process; technical adequacy of the lateral must still be confirmed (superimposed epicondyles).
• “Mid-shaft humerus fracture, patient in severe pain” → two projections 90° apart including joints; transthoracic or horizontal-beam lateral rather than aggressive arm rotation.

RTR competence here is equal parts anatomy, projection library, and refusing to create secondary injury for a perfect picture.