We studied 37 fractures lateral to the spinoglenoidal notch to evaluat
e the validity of collectively handling these fractures as an acromion
fracture and to ascertain the mechanism of injury. We divided them in
to three groups according to the location of the fracture line. Fractu
re of the anatomic acromion or the extremely lateral scapular spine (g
roups I and II, 28 fractures) was frequently associated with fracture
of the coracoid base, acromioclavicular joint injury, or both. The mec
hanism of injury in most cases was presumed to be indirect force broug
ht to bear on the shoulder from the lateral direction. Fracture descen
ding to the spinoglenoidal notch (group III, nine fractures) was seldo
m associated with other shoulder injuries, and surgery was rarely need
ed. The mechanism was assumed to be direct force brought to bear on th
e shoulder from the posterior direction. Therefore fractures of the an
atomic acromion and the extremely lateral scapular spine may be manage
d collectively. However, fracture descending to the spinoglenoidal not
ch should be managed separately. We advocate that these fractures shou
ld be classified into two types in terms of-clinical consideration: ty
pe I fractures, comprising those of the anatomic acromion and the extr
emely lateral scapular spine, and type II fractures, located in the mo
re medial spine and descending to the spinoglenoidal notch.