Modern Study Review (AI-Generated)
High-Yield Summary
The AO/OTA 21 classification pertains to fractures of the proximal radius and ulna, a critical region for elbow stability and forearm rotation. This classification guides surgical decision-making by distinguishing extra-articular (Type A), partial articular (Type B), and complete articular (Type C) fractures, with increasing complexity and instability from A to C. Understanding the fracture morphology directly influences the choice between conservative management, absolute stability fixation, or bridging techniques to restore joint congruity and function.
Anatomy & Coding Foundation
- AO Code: 21 = Proximal Radius and Ulna
- Segments:
- 1 = Proximal radius
- 2 = Proximal ulna
- 3 = Both bones involved proximally
- Morphology Types:
- A (Extra-articular): Fractures not involving the joint surface
- B (Partial articular): Fractures involving part of the joint surface with some articular continuity
- C (Complete articular): Fractures involving the entire articular surface with complete separation from the shaft
Classification Details
| AO Type | Subtype | Description | Bone Involvement | Injury Mechanism | Stability Profile |
| A | 1 | Extra-articular fracture, ulna intact | Radius fractured only | Low-energy trauma, direct blow | Generally stable |
| 2 | Extra-articular fracture, radius intact | Ulna fractured only | Direct trauma | Generally stable | |
| 3 | Extra-articular fracture, both bones fractured | Both radius and ulna fractured | High-energy trauma | Potentially unstable | |
| B | 1 | Partial articular, ulna fractured, radius intact | Ulna articular fracture | Rotational or axial load | Unstable, joint incongruity possible |
| 2 | Partial articular, radius fractured, ulna intact | Radius articular fracture | Rotational or axial load | Unstable, joint incongruity possible | |
| 3 | One bone intra-articular, other extra-articular | Mixed pattern | Complex trauma | Unstable | |
| C | 1 | Complete articular, simple articular fracture | Both bones, simple articular | High-energy trauma | Highly unstable |
| 2 | Complete articular, one simple + one comminuted | One bone simple, other comminuted | High-energy trauma | Highly unstable | |
| 3 | Complete articular, both bones comminuted | Both bones comminuted | Severe trauma | Highly unstable |
Management Logic
- Operative Indications:
- Type A fractures with minimal displacement may be managed non-operatively.
- Types B and C generally require surgical fixation to restore articular congruity and forearm stability.
- Comminuted (C2, C3) fractures often necessitate ORIF with plates or intramedullary devices, sometimes combined with external fixation in severe cases.
- Fixation Principles:
- Absolute Stability: Required for articular fractures (Types B and C) to allow early motion and prevent post-traumatic arthritis. Achieved via compression plating or lag screws.
- Relative Stability: May be acceptable for extra-articular fractures (Type A) with bridge plating or intramedullary nailing to preserve biology and allow callus formation.
Prognostic Factors
- Increasing AO grade correlates with:
- Higher risk of non-union and malunion, especially in comminuted (C3) fractures.
- Greater likelihood of post-traumatic arthritis due to articular surface involvement.
- Need for more complex surgical reconstruction and longer rehabilitation.
- Early anatomical reduction and stable fixation improve functional outcomes and reduce complications.
Classic Clinical Notes
- A – Extra-articular
- 21-A-1: Ulna fractured, radius intact
- 21-A-2: Radius fractured, ulna intact
- 21-A-3: Both bones fractured
- B – Articular
- 21-B-1: Ulna fractured, radius intact
- 21-B-2: Radius fractured, ulna intact
- 21-B-3: One intra-articular + other extra-articular
- C – Articular (both bones)
- 21-C-1: Simple articular
- 21-C-2: One simple + one comminuted
- 21-C-3: Both comminuted
Last Updated on January 25, 2026 by Christian Veillette
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