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Tadato Kido, MD et al ABSTRACT The same laboratory that provided
this study also reported in the past how the rotator cuff musculature
along with the biceps provide anterior stabilization to the shoulder in
abduction and external rotation. Other
studies have revealed that the deltoid, which makes up 20% of the muscle
mass of the shoulder, may also play a role in stabilization by the way the
electromyography reveals itself. This
time, the authors wanted to provide evidence that the deltoid is an
anterior stabilizer of the shoulder, especially in external rotation and
abduction. Nine fresh-frozen cadaver shoulders
were placed on an apparatus that stabilized the scapula while the arm was
moved into 90 degrees of abduction and 90 degrees of external rotation.
The humeral head position was monitored by an electromagnetic
tracking device while 1.5kg of force was applied to the head anteriorly,
while up to 5kg of force was placed through each of the three deltoid
heads. The first test performed, with an
intact anterior capsule, revealed that as the deltoid was loaded to
simulate contraction, the anterior displacement decreased. When the capsule was vented, anterior translation occurred
until the simulation of the deltoid was activated, and then there was a
significant reduction of the displacement.
The last test simulated a Bankart lesion, where again the deltoid
was able to significantly reduce the anterior translation. These authors feel that deltoid
strengthening should be part of any shoulder rehabilitation involving
anterior laxity of the shoulder. COMMENTS When treating patients with
anterior laxity, my approach was always to strengthen ALL muscles that
cross the shoulder, including the biceps, latissimus, triceps (which
stabilize while the biceps contracts), coracobrachialis, and the deltoids.
Often, simple rotator cuff exercises will also incorporate the
deltoid, but often not enough to load and provide adequate strengthening.
Use of military press, upright rows, and bench press will address
the area. Closed chain strengthening, such as push-ups and ball
stabilization can also be used. Electrical
stimulation, or Russian stimulation, is also an option to augment the
program. If all goes
well tomorrow, I plan on taking a large grouping of photographs, and a few
methods to strengthen the posterior deltoid are in the plans.
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