AO classification of 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
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 .