Classification system
Mason Classification
Mason Classification of Radial Head Fractures
The Mason classification sorts radial head fractures into four types — non-displaced (I), displaced partial articular (II), comminuted involving the whole head (III), and any radial head fracture accompanied by an elbow dislocation (IV) — and the type broadly separates fractures managed non-operatively from those needing fixation or replacement.
What the Mason category means
Mason categories describe different patterns, not increasing severity — a higher-lettered or higher-numbered category is not necessarily a worse problem. The groups below are descriptive.
- Reconstructable or non-operative (types I–II)1–2
Type I is almost always non-operative. Type II turns on whether forearm rotation is mechanically blocked, which is a clinical finding, not a radiographic one.
- Usually operative (types III–IV)3–4
Type III usually needs arthroplasty rather than fixation. Type IV is an unstable elbow injury in which the radial head must not simply be excised.
Published criteria and reliability
The published cut-offs that define this instrument, and the measured agreement between observers using it. Each is reported with the population it was derived in.
| Type | Value | Subscale | Population | Follow-up | Source |
|---|---|---|---|---|---|
| Criterion | Displacement of 2 mm or more, or involvement of 30% or more of the articular surface, separates type I from type II | — | Radial head fractures assessed on plain radiographs or CT | — | Broberg MA 1987 |
| Criterion | Any radial head fracture with an associated elbow dislocation is type IV, whatever the fracture pattern | — | Radial head fracture-dislocations | — | Johnston GW 1962 |
| Criterion | Interobserver reproducibility of the Mason types is only fair to moderate, with most disagreement at the type I–II boundary | — | Orthopaedic surgeons classifying proximal radius fractures from radiographs | — | Matsunaga FT 2009 |
Criterion is a published cut-off, definition or performance figure belonging to a classification or decision rule — it is not a change score and should not be read as one.
How the score is calculated
Stated in full so the calculation can be independently checked, and reproduced by hand if needed.
Type I is a non-displaced or minimally displaced fracture of the radial head or neck, conventionally less than 2 mm of displacement, with no mechanical block to forearm rotation. Type II is a partial articular fracture displaced 2 mm or more, or involving 30% or more of the articular surface — the numeric criteria are Broberg and Morrey’s later quantification of Mason’s descriptive types. Type III is a comminuted fracture involving the entire head. Type IV, added by Johnston, is any radial head fracture occurring with a dislocation of the elbow, and is assigned on the basis of the dislocation rather than the fracture pattern; the pattern is still recorded because it determines whether the head is reconstructable. Hotchkiss later proposed a functional modification in which types I to III are separated by whether forearm rotation is mechanically blocked and whether the fracture is reconstructable, which is closer to how the classification is actually used to choose treatment.
Instrument profile
- Developer
- Michael L. Mason; type IV added by G. W. Johnston
- Institution
- Northwestern University, Chicago, United States
- First published
- 1954
- Items
- 2
- Response format
- Two radiographic and clinical findings
- Score range
- 1 to 4
- Direction
- Categories are not ranked by severity
- Completion time
- About 1 minutes
- Regions
- Elbow
- Conditions
- Radial head fracture, Elbow dislocation, Terrible triad of the elbow, Elbow fracture-dislocation
- Procedures
- Open reduction and internal fixation of the radial head, Radial head arthroplasty, Radial head excision, Elbow ligament repair
- Validity
- The type broadly tracks treatment: type I non-operative, type III arthroplasty or excision, type IV an unstable elbow. It predicts the need for surgery better than it predicts the functional outcome, which depends more on the associated ligament and coronoid injuries than on the radial head fracture itself.
- Reliability
- Agreement is only fair to moderate on plain films because the type I–II boundary is a 2 mm measurement; CT improves both agreement and the detection of comminution.
When to use the Mason
Well suited to
- Describing a radial head fracture in a clinic letter or operation note in terms other surgeons will read the same way.
- Triaging a radial head fracture towards non-operative treatment, fixation or replacement.
- Flagging the fracture-dislocation (type IV) that must not be treated by radial head excision alone.
Limitations and poor fits
- As a stability assessment. The type describes the fracture, not the elbow — a type II with a torn medial collateral ligament and a coronoid fracture behaves nothing like an isolated type II.
- Deciding on a type II without first testing forearm rotation for a mechanical block, which is the finding that actually separates operative from non-operative treatment.
- Classifying radial neck fractures in children, where the Judet classification and angulation thresholds apply instead.
- Claiming precision the plain radiographs do not support — if the 2 mm distinction changes the plan, get the CT.
Mason compared with other instruments
Instruments measuring a related construct, with the practical difference between them.
| Instrument | Items | Range | What it adds |
|---|---|---|---|
| AO/OTA | 3 | 1–3 | The AO/OTA classification gives every fracture an alphanumeric code in which the first digit is the bone, the second the segment and the letter the fracture type — extra-articular, partial articular or complete articular in an end segment, and simple, wedge or multifragmentary in a shaft — so that 32-A is a simple femoral shaft fracture and 43-C a complete articular pilon fracture. |
| Kellgren-Lawrence | 1 | 0–4 | The Kellgren-Lawrence classification grades radiographic osteoarthritis from 0 to 4 based on osteophyte formation, joint space narrowing, subchondral sclerosis and bone contour deformity, with grade 2 conventionally taken as the threshold for definite radiographic osteoarthritis. |
| QuickDASH | 11 | 0–100 | The QuickDASH is an 11-item shortened form of the DASH that measures physical function and symptoms across the whole upper limb on a single 0 to 100 scale, where a higher score means greater disability. |
Copyright and permitted use
Published openly because it is the question every clinician and researcher asks before using an instrument, and almost nobody answers it.
A published radiographic classification system. No licence is required.
References
- Mason ML. Some observations on fractures of the head of the radius with a review of one hundred cases. British Journal of Surgery. 1954.
- Johnston GW. A follow-up of one hundred cases of fracture of the head of the radius with a review of the literature. Ulster Medical Journal. 1962.
- Broberg MA, Morrey BF. Results of treatment of fracture-dislocations of the elbow. Clinical Orthopaedics and Related Research. 1987.
- Hotchkiss RN. Displaced fractures of the radial head: internal fixation or excision?. Journal of the American Academy of Orthopaedic Surgeons. 1997.
- Matsunaga FT, Tamaoki MJS, Cordeiro EFO, et al.. Are classifications of proximal radius fractures reproducible?. BMC Musculoskeletal Disorders. 2009.
Editorial status
This page has not yet been signed off by a named clinical reviewer. The scoring logic is stated in full above so it can be independently verified, and every threshold is traceable to its source. See our editorial methodology.