Understanding the Mason Classification of Radial Head Fractures

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### High-Yield Summary

– The Mason classification stratifies radial head fractures by displacement and comminution, directly guiding management from non-operative care to complex reconstruction or arthroplasty.
– Type I fractures are nondisplaced or minimally displaced and typically managed non-operatively with early motion.
– Type II fractures involve displacement >2 mm or mechanical block and often require open reduction and internal fixation (ORIF).
– Type III fractures are comminuted and unstable, frequently necessitating radial head excision with replacement arthroplasty to restore elbow stability.
– Accurate classification depends on high-quality imaging, including true anteroposterior and lateral radiographs, supplemented by CT for complex or comminuted fractures.

### Clinical Fundamentals

#### Relevant Anatomy
The radial head articulates with the capitellum and the radial notch of the ulna, contributing to elbow stability and forearm rotation. The lateral collateral ligament complex attaches near the radial head, making its integrity critical for varus and posterolateral rotatory stability.

#### Biomechanics
The radial head transmits axial load from the wrist to the humerus, bearing up to 60% of the load in valgus stress. Loss of radial head integrity compromises elbow stability, especially in the presence of ligamentous injury or coronoid fractures.

#### Epidemiology
Radial head fractures account for approximately one-third of all elbow fractures, predominantly occurring in adults aged 30-50 years after a fall on an outstretched hand with the elbow partially flexed.

### Classification & Diagnosis

| Mason Type | Description | Key Diagnostic Features | Management Implication |
|————|———————————————-|—————————————————-|———————————————|
| Type I | Nondisplaced or minimally displaced (<2 mm) | No mechanical block, stable elbow on exam | Non-operative, early mobilization |
| Type II | Displaced (>2 mm), single fragment | Mechanical block or limited range of motion | ORIF to restore articular congruity |
| Type III | Comminuted, displaced | Multiple fragments, unstable elbow | Radial head excision or arthroplasty |
| Type IV* | Radial head fracture with elbow dislocation | Associated ligamentous injury and instability | Surgical stabilization of fracture and ligaments |

*Type IV is a modification by Johnston, emphasizing associated dislocation.

#### Diagnostic Pearls
– Obtain true AP and lateral elbow radiographs with the forearm in neutral rotation to avoid underestimating displacement.
– CT scans are essential for assessing comminution and fragment size in Type II and III fractures.
– Beware of subtle mechanical blocks indicating intra-articular fragment displacement, which mandates surgical intervention.

### Decision-Making Algorithm

| Criteria | Non-Operative Management | Operative Management |
|————————————-|————————————————–|————————————————-|
| Displacement <2 mm, no mechanical block | Immobilization <1 week, early active motion | Not indicated |
| Displacement >2 mm, mechanical block | Contraindicated | ORIF with headless screws or mini-plates |
| Comminution with instability | Contraindicated | Radial head arthroplasty preferred over excision alone |
| Associated elbow dislocation | Rarely non-operative | Combined fracture fixation and ligament repair |

#### Surgical Approach and Implant Choice
– The Kocher interval (between anconeus and extensor carpi ulnaris) provides safe lateral access.
– Headless compression screws are preferred for large fragments in Type II fractures.
– For comminuted fractures, modular radial head arthroplasty restores stability and load transmission better than excision alone.

### Surgical Mastery & Pearls

#### Step-by-Step Conceptual Overview
1. Position the patient supine or lateral decubitus with the arm on an arm board to allow full elbow flexion and extension intraoperatively.
2. Identify and protect the posterior interosseous nerve during lateral exposure.
3. Use the Kocher approach to access the radial head, avoiding excessive soft tissue stripping to preserve blood supply.
4. For Type II fractures, achieve anatomic reduction with provisional K-wires, then secure with headless screws ensuring subchondral support.
5. In Type III fractures, assess the feasibility of fixation; if not reconstructible, proceed with modular arthroplasty sized to restore radial length and avoid overstuffing.
6. Confirm elbow stability through full range of motion after fixation or arthroplasty.
7. Repair lateral collateral ligament complex if injured to prevent posterolateral rotatory instability.

#### Intraoperative Red Flags
– Excessive stripping of soft tissues leading to avascular necrosis risk.
– Overstuffing the radial head prosthesis causing limited motion and capitellar wear.
– Failure to recognize and address associated ligamentous injuries resulting in chronic instability.

### Evidence-Based Synthesis

Recent randomized controlled trials and meta-analyses have refined the management of Mason Type II and III fractures. Evidence supports non-operative treatment for minimally displaced fractures with excellent functional outcomes and low complication rates. For Type II fractures, ORIF improves range of motion and reduces mechanical block compared to conservative care, but fixation failure rates increase with comminution.

In comminuted Type III fractures, radial head arthroplasty has demonstrated superior elbow stability and functional scores compared to excision alone, particularly in the setting of ligamentous injury. However, controversy persists regarding the optimal implant design and long-term outcomes, with some studies reporting polyethylene wear and capitellar erosion.

The literature underscores the importance of restoring radial length and addressing concomitant soft tissue injuries to optimize outcomes. Surgical timing and early mobilization protocols remain areas of ongoing investigation, with emerging data favoring early motion to prevent stiffness without compromising fixation.

### Master Class Pro-Tip

Mastery in managing radial head fractures hinges on appreciating the radial head as a keystone of elbow stability rather than a mere fracture fragment. Prioritize anatomic restoration of the articular surface and radial length while meticulously preserving soft tissue attachments. When arthroplasty is indicated, intraoperative trialing to avoid overlengthening is critical-use fluoroscopy to compare radial height with the contralateral side. Finally, always assess and address lateral collateral ligament integrity intraoperatively; failure to do so is the most common cause of postoperative instability and poor functional outcomes.

Last Updated on July 10, 2026 by OrthoNet AI