AO Classification 12 – Humeral Diaphysis

Modern Study Review (AI-Generated)

High-Yield Summary

The AO/OTA classification 12 refers to fractures of the humeral diaphysis (shaft). This classification stratifies fractures by morphology into simple (A), wedge (B), and complex (C) types, which directly influence surgical decision-making regarding stability and fixation strategy. Understanding the fracture pattern guides the choice between absolute stability (compression plating) and relative stability (intramedullary nailing or bridge plating), optimizing healing and functional outcomes.

Anatomy & Coding Foundation

• AO Code: 12 (Humeral diaphysis)
• Bone: 1 (Humerus)
• Segment: 2 (Diaphysis/shaft)
• Morphology Types:
• A: Simple fractures
• B: Wedge (segmental) fractures
• C: Complex fractures

Classification Details

Management Logic

• Operative Indications:
• AO Type A fractures may be treated non-operatively if alignment and stability are acceptable.
• Types B and C generally require surgical fixation due to instability and risk of non-union.
• Segmental and comminuted fractures (B3, C2, C3) often need ORIF or intramedullary nailing. External fixation is reserved for open or highly comminuted fractures with soft tissue compromise.

• Fixation Principles:
• Absolute Stability: Compression plating preferred for simple (A) fractures to promote primary bone healing.
• Relative Stability: Bridge plating or intramedullary nailing for wedge (B) and complex (C) fractures to allow secondary healing with callus formation.

Prognostic Factors

• Simple fractures (A1-A3): Low non-union rates, good prognosis with appropriate fixation or conservative treatment.
• Wedge fractures (B1-B3): Increased risk of delayed union/non-union due to segmental instability.
• Complex fractures (C1-C3): Highest risk of complications including non-union and malunion; require meticulous surgical technique and stable fixation.
• Post-traumatic stiffness and radial nerve palsy risk increase with complexity and comminution.

Classic Clinical Notes

• A-Simple fracture
• 12-A-1 spiral
• 12-A-2 oblique (>30 degrees)
• 12-A-3 transverse (<30)

• B-SegmentalWedge
• 12-B-1 spiral wedge
• 12-B-2 bending wedge
• 12-B-3 fragmented wedge

• C-Complex Fracture
• 12-C-1 spiral
• 12-C-2 segmental
• 12-C-3 irregular

Last Updated on January 25, 2026 by Christian Veillette