UCSD Musculoskeletal Radiology
The Neer classification of proximal humerus fractures
The proximal humerus is made up of four parts:
These four parts are separated by epiphyseal lines (bone growth plates) during the early developmental years. When the proximal humerus is broken, the fracture line predictably occurs along one or more of these planes.
Displacement of a fracture fragment by 1 cm, or angulation between fracture fragments of 45° or greater, is what defines a fragment as being a "separate" part. Hence, a proximal humerus fractures may be called 2-part, 3-part, or 4-part according to the Neer classification system, depending upon the amount of displacement and angulation seen on x-ray.
Neer CS 2nd: Displaced proximal humeral fractures. I. Classification and evaluation. J Bone Joint Surg Am 1970 Sep; 52(6): 1077-89