Radial Head Fractures and Mason Classification
On this page
Direct answer
A radial head fracture is a break of the proximal radius at its joint with the capitellum, and the Mason classification grades it from type I, nondisplaced, to type IV, associated with elbow dislocation. A displaced fragment can block forearm rotation, which is the main functional concern. Type I fractures move early, displaced type II fractures are usually fixed, comminuted type III is replaced or excised, and type IV depends on the dislocation.
What you must remember
- Mason I: a nondisplaced fracture, often small, managed with early mobilisation and a sling for comfort.
- Mason II: a displaced fracture with a single large fragment, usually fixed with small screws when the fragment can be reconstructed.
- Mason III: a comminuted head that cannot be reconstructed, managed by replacement or excision.
- Mason IV: a radial head fracture with elbow dislocation, where elbow stability guides the choice, and replacement is often preferred.
- Mechanical block: a displaced fragment or comminution obstructs pronation and supination and must be treated rather than simply rehabilitated.
- Excision caution: excision is acceptable in isolated injuries, but an interosseous membrane tear makes proximal radioulnar migration (Essex-Lopresti) a risk.
- Associated injuries: coronoid, ligament and interosseous membrane injuries are checked, since they change the plan.
Mason types compared
The Mason grade is the first step in the decision, and each grade points towards a treatment. The table lists the usual pattern for each grade.
| Mason type | Pattern | Usual treatment |
|---|---|---|
| I | Nondisplaced | Early motion and sling |
| II | Displaced single fragment | Open reduction and internal fixation |
| III | Comminuted | Replacement or excision |
| IV | With elbow dislocation | Replacement and elbow stabilisation |
The grade alone does not settle management, since associated injuries and the presence of a mechanical block shift the plan. Excision is most reliable when the elbow is otherwise stable, and it is avoided when the forearm or ligaments are at risk. An examiner usually rewards the candidate who names the associated injury that changes the decision.
Where the exam tries to catch you
Radial head questions often hinge on whether the candidate notices what else is damaged.
- Trap: excising a radial head in a patient with an interosseous membrane tear Correct: excision risks proximal migration of the radius, so replacement is preferred in that setting.
- Trap: assuming a nondisplaced fracture is always benign Correct: check the elbow for coronoid, ligament and interosseous injuries, which change the plan.
- Trap: reading a rotation block as a stiffness problem only Correct: a displaced fragment blocks rotation mechanically, which needs a fixation decision rather than physiotherapy alone.
Frequently asked questions
What defines a Mason type II radial head fracture?
Mason type II is a displaced fracture with a single large fragment, usually involving a portion of the head that can be reconstructed. It typically needs open reduction and internal fixation when the fragment is suitable.
Why is radial head excision avoided in some patients?
Excision is avoided when an interosseous membrane injury is present, because the radius can migrate proximally, which is the Essex-Lopresti pattern. Replacement with a prosthesis is generally preferred in that setting.
What is a mechanical block in radial head fracture?
A mechanical block occurs when a displaced fragment or comminution obstructs forearm rotation, usually limiting pronation and supination. It signals the need for fixation, replacement or excision rather than rehabilitation alone.
Which Mason type is associated with elbow dislocation?
Mason type IV is a radial head fracture associated with elbow dislocation. The stability of the elbow and any ligament repair guide the choice of treatment for this type.