Fractures of the acromion and the lateral scapular spine.

We studied 37 fractures lateral to the spinoglenoidal notch to evaluate the validity of collectively handling these fractures as an acromion fracture and to ascertain the mechanism of injury. We divided them into three groups according to the location of the fracture line. Fracture of the anatomic acromion or the extremely lateral scapular spine (groups I and II, 28 fractures) was frequently associated with fracture of the coracoid base, acromioclavicular joint injury, or both. The mechanism of injury in most cases was presumed to be indirect force brought to bear on the shoulder from the lateral direction. Fracture descending to the spinoglenoidal notch (group III, nine fractures) was seldom associated with other shoulder injuries, and surgery was rarely needed. The mechanism was assumed to be direct force brought to bear on the shoulder from the posterior direction. Therefore fractures of the anatomic acromion and the extremely lateral scapular spine may be managed collectively. However, fracture descending to the spinoglenoidal notch should be managed separately. We advocate that these fractures should be classified into two types in terms of clinical consideration: type I fractures, comprising those of the anatomic acromion and the extremely lateral scapular spine, and type II fractures, located in the more medial spine and descending to the spinoglenoidal notch.