Vaisman et al reported a radiographic index for the diagnosis of a posterior acromioclavicular joint dislocation. The authors are from Clinica Alemana de Santiago Universidad del Desarrollo Santiago in Chile.
Exam: bilateral Zanca radiographic views
Measurements:
(1) width of AC joint on injured side in mm
(2) width of AC joint on normal side
index =
= ((width on injured side) - (width on normal side)) / (width of normal side) * 100%
Rockwood Classification
Mean Width
Range
I
2.1
-12 to 25
II
4.2
-19 to 29
III
19.1
-59 to 91
IV
110.3
47 to 181
V
-3.8
-71 to 62
These show overlap between the categories. Types I and II are similar.
A value > 30% would be seen in Types III, IV and V.
A value < -20 would be seen in Types III and V.
A value > 91% is seen in Type IV. A negative index excludes Type IV.
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