| Stress
fractures of the first rib in athletes are rare. A 14-year-old male,
a baseball pitcher who changed from an overhand to a sidearm style,
with a stress fracture of the first rib, was reported. Most Stress
fractures in the first rib occur at the subclavian groove, between
the attachments of the scalenus anterior and scalenus medius muscles,
which is the thinnest and weakest portion of the rib. However, in
this case the stress fracture occurred at the uncommon region, posterior
to the insertion of the scalenus medius muscle, in the first rib.
The motion analysis of the pitching in this case demonstrated that
the sidearm style induced much more horizontal abduction in the shoulder
at the top position than did the overhand style. The findings of electromyography
in the serratus anterior muscle, one of the muscles which insert on
the first rib, through the pitching motion did not demonstrate any
significant differences between the two styles. In this case, the
repetition of horizontal over-abduction of the shoulder when sidearm
pitching appears to have been the cause of the unusual stress fracture
of the first rib at this site.
KEY
WORDS: Motion analysis, horizontal abduction, electromyography,
serratus anterior muscle.
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