AO Classification 11 - Proximal Humerus

Modern Study Review (AI-Generated)

High-Yield Summary

The proximal humerus (AO 11) fractures involve the upper segment of the humerus, including the humeral head, greater and lesser tuberosities, and metaphysis. The AO/OTA classification stratifies these fractures by articular involvement and complexity, guiding surgical decision-making between conservative management and operative fixation. Understanding the fracture morphology (A: extra-articular unifocal, B: extra-articular bifocal, C: articular) is critical for determining stability and the need for anatomical reduction or joint preservation.

Anatomy & Coding Foundation

AO Code: 11 (Proximal Humerus)
Segment:
11-A: Extra-articular unifocal fractures
11-B: Extra-articular bifocal fractures
11-C: Articular fractures involving the humeral head
Morphology Types:
A: Simple, extra-articular fractures (single focus)
B: Bifocal, extra-articular fractures (two fracture lines, metaphyseal involvement)
C: Complex articular fractures involving the glenohumeral joint

Classification Details

AO Type	Subtype	Description	Injury Mechanism	Stability Profile
11-A	A1	Tuberosity fracture	Avulsion or direct trauma	Generally stable
	A2	Impacted metaphyseal fracture	Axial load with impaction	Stable, impacted fragment
	A3	Non-impacted metaphyseal fracture	Direct trauma, no impaction	Potentially unstable
11-B	B1	Bifocal with metaphyseal impaction	High-energy trauma	Moderately unstable
	B2	Bifocal without impaction	Direct or indirect trauma	Unstable
	B3	Bifocal with glenohumeral dislocation	Dislocation with fracture	Highly unstable
11-C	C1	Articular fracture, slight displacement	Low-energy trauma	Potentially stable if minimal displacement
	C2	Impacted and displaced articular fracture	High-energy trauma	Unstable, joint incongruity
	C3	Articular fracture with glenohumeral dislocation	Severe trauma	Highly unstable, requires reduction

Management Logic

Operative Indications:
11-A: Usually non-operative unless tuberosity displacement >5 mm or functional impairment.
11-B: ORIF or intramedullary nailing indicated for unstable bifocal fractures, especially with metaphyseal comminution or dislocation.
11-C: Requires anatomical reduction and fixation (ORIF) due to articular involvement; dislocations necessitate urgent reduction and stabilization.

Fixation Principles:
Absolute Stability: Required for articular fractures (11-C) to restore joint congruity and prevent post-traumatic arthritis.
Relative Stability: Acceptable for extra-articular fractures (11-A, 11-B) with bridge plating or intramedullary devices allowing secondary bone healing.

Prognostic Factors

11-A: Good prognosis with low non-union rates; tuberosity involvement may affect rotator cuff function.
11-B: Increased risk of malunion and stiffness due to metaphyseal comminution and instability.
11-C: Highest risk of post-traumatic arthritis and avascular necrosis; displacement and dislocation worsen outcomes.

Classic Clinical Notes