AO classification of proximal humeral fractures

The AO classification of proximal humeral fractures, along with the Neer classification, is one of the most frequently used systems for classifying proximal humeral fractures.

The AO classification divides proximal humeral fractures into three groups, A, B and C, each with subgroups, and places more emphasis on the blood supply to the articular surface . The assumption is that if either the lesser or greater tuberosity remains attached to the articular segment, then blood supply is probably adequate to avoid avascular necrosis .

  • type A: extra-articular unifocal (either tuberosity +/- surgical neck of the humerus
    • A1: extra-articular unifocal fracture 
    • A2: extra-articular unifocal fracture with impacted metaphyseal fracture
    • A3: extra-articular unifocal fracture with non-impacted metaphyseal fracture
  • type B: extra-articular bifocal (both tuberosities +/- surgical neck of the humerus or glenohumeral dislocation)  
    • B1: extra-articular bifocal fractures with impacted metaphyseal fracture
    • B2: extra-articular bifocal fractures with non-impacted metaphyseal fracture
    • B3: extra-articular bifocal fractures with glenohumeral joint dislocation
  • type C: extra-articular (anatomical neck) but with compromise to the vascular supply of the articular segment
    • C1: anatomical neck fracture, minimally displaced
    • C2: anatomical neck fracture, displaced and impacted
    • C3: anatomical neck fracture with glenohumeral joint dislocation

The risk of avascular necrosis increases from type A (very low) to type C (high risk) and thus determines treatment (see proximal humeral fractures) .

As is the case with the Neer classification, due to the combination of complex anatomy and complex classification system, inter-observer and even intra-observer reproducibility is poor .

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