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January 2002
By Theodore E. Keats, MD
After injuring his shoulder in a fall, a 40-year-old man has pain
when the shoulder is moved. What is your interpretation of the frontal
(top) and axillary (bottom) views of his shoulder?
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ANSWER
The man has os acromiale, a normal variant of the joint between
the acromion and the scapular spine. It is seen most clearly in
the axillary projection as an apparent fracture of the acromion
(arrows). This variant occurs when the secondary ossification center
of the acromion fails to unite with the parent bone, remaining as
an isolated osseous element. It can be distinguished from a fracture
by its irregular junction with the main portion of the acromion;
fractures, in contrast, are usually straight and sharply delineated.
This condition may be unilateral or bilateral.
For further reading, see T.E. Keats: An Atlas of Normal Roentgen
Variants That May Simulate Disease, 6th ed. Philadelphia, Mosby,
1996, p. 343.
Emerg Med 34(1):67, 2002
This series of diagnostic quizzes that challenge your ability
to read a variety of x-ray films is edited by Dr. Keats, professor
of radiology and professor of orthopedics at the University of Virginia
School of Medicine in Charlottesville.
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