Background: The 4-segment classification of Neer (1970) was revised in 2002 with the inclusion of valgus-impacted fractures. However, the range of possible fracture types covered by this classification is not clear. With the aim to clarify actual fracture patterns of the proximal humerus, a retrospective, multicenter study was conducted.
Methods: We retrospectively reviewed 509 cases for which anteroposterior and trans-scapular lateral views had been taken at the time of injury. Initially, three examiners from three facilities, independently read the radiographs of each case. In the second and third phases, for more difficult cases, consensus opinions were reached.
Results: We found that 501 (98%) of the 509 fractures had an appropriate category in the revised Neer classification. There were 185 cases (36%) of one-part fractures, followed by 156 cases (31%) of 2-part surgical neck fracture, 60 cases (12%) of 2-part greater tuberosity fracture (dislocation included), 45 cases (8.8%) of 3-part fracture involving the greater tuberosity and the surgical neck (dislocation included), 31 cases (6.1%) of 4-part fracture (dislocation included), and 17 cases (3.3%) of valgus-impacted fracture.Eight fractures (1.6%) could not be classified with the revised Neer classification. They were "3-part" fractures in terms of the number of displaced segments but had a complete anatomic neck fracture.
Conclusion: We conclude that it would be appropriate to use the revised Neer classification in clinical practice. We would emphasize that, when there are 3 displaced segments, close attention should be paid to the fracture line on the anatomic neck.
Level of evidence: Level 4; Diagnostic study, case series.