First and second year — the floor first, then every step
In an adult, a displaced fat pad means a fracture — usually the radial head. Then look for the combination that destabilises the elbow: dislocation with radial head and coronoid fractures (the terrible triad).
Orient first
The radial head is the commonest adult elbow fracture and can be invisible on the first film; the posterior fat pad is the clue.
The coronoid process is the anterior buttress; a coronoid fracture with a dislocation makes the elbow unstable.
The radiocapitellar line must pass through the capitellum on every view — if it does not, the radial head is dislocated.
Acquire the study
AP and true lateral; radial head–capitellum (Greenspan) view when the head is not seen clearly.
The manoeuvre
True lateral view: anterior "sail" and posterior fat pad elevation.
Radial head and neck on both views: cortical step, impaction or angulation.
Radiocapitellar and ulnohumeral alignment on the lateral view.
Coronoid tip on the lateral view — a small fleck anterior to the ulnohumeral joint.
Olecranon and the distal humerus (condyles and epicondyles).
What confirms it
A fracture line; a positive posterior fat pad in an adult implies one.
What licenses you to exclude it
A normal radiograph with a posterior fat pad does not exclude a fracture.
The classic misread
Missing a coronoid tip fracture that makes a dislocation a terrible triad.
Radial head fragment displacement in mm (> 2 mm articular step is commonly treated — verify); coronoid fragment height.
What to report
Each fracture with its classification; displacement; joint alignment; the combination (terrible triad: dislocation + radial head + coronoid).
How to report it
CT: "Posterior elbow dislocation with a comminuted radial head fracture (Mason III) and a coronoid tip fracture (Regan–Morrey I) — terrible triad injury."
What not to report
Do not report "no fracture" with a posterior fat pad present; report the effusion and a probable occult radial head fracture.
Associated injuries to look for
Medial and lateral collateral ligament injury, Essex-Lopresti injury (radial head fracture with interosseous membrane and DRUJ injury).
What changes management
Terrible triad → operative fixation.
A radial head fracture with wrist pain → image the DRUJ (Essex-Lopresti).
Reference values
Each value carries the caveat that keeps it from being misused. Normal limits and diagnostic criteria are kept apart on purpose: a disease cut-off read as a normal range is the more dangerous mistake.
Normal limits
Elbow (ulnohumeral) · Olecranon–coronoid relationship and ulnohumeral alignment
the trochlear notch is a congruent C; a line along the anterior humeral cortex still hits the capitellum (see that entry), and the coronoid should sit in the fossa on a true lateral
A drop of the coronoid out of the fossa is the posterior-dislocation remnant. True-lateral technique is the measurement.
a congruent radiocapitellar space on every projection (the radiocapitellar-line entry is the alignment companion); isolated space loss is uncommon and usually technical
A dropped radiocapitellar line is Monteggia / dislocation, not “joint-space narrowing”. True lateral first.
X-ray
Diagnostic criteria
Radial head (Mason) · Mason / Hotchkiss grade of radial-head fracture
a named I–III (Hotchkiss adds the Mason IV dislocation): undisplaced, displaced, comminuted — CT defines articular step and fragment count that radiographs miss
Look for the Essex-Lopresti and the coronoid (terrible triad). A “simple” Mason I still needs a true-lateral DRUJ if the mechanism is longitudinal.
X-ray · CT
See it on real cases
Direct links to Radiopaedia — the reference article and worked cases with their images. Each opens on Radiopaedia.