The Rotator
Cuff
The shoulder is made up of three bones: the
scapula (shoulder blade), the humerus (upper arm bone) and the
clavicle (collarbone). The shoulder joint is designed for
mobility. In order to allow freedom of movement (just imagine
all the directions your shoulder goes in), the shoulder joint has less
stability. The dynamic stability of the shoulder ball-and-socket
joint is mainly provided by the rotator cuff.
Four muscles that attach from the shoulder blade, and wrap around the
front, back, and top of the upper arm bone form the rotator
cuff. These muscles are called the supraspinatus, infraspinatus,
teres minor, and subscapularis. The larger deltoid muscles cover
these muscles and move the arm after motion is initiated by the
rotator cuff.
The rotator cuff muscles are responsible for
keeping the large ball sliding and gliding smoothly and securely in
the smaller shoulder socket. As the arm is raised, the rotator
cuff keeps the humerus tightly in the socket of the scapula (similar
to golf ball on a tee). To do this, the rotator cuff pulls the
shoulder bone down and compresses it into the socket. To a
lesser degree the rotator cuff also helps to rotate and spin the arm
around in its socket.
There are two major causes of most shoulder injuries. Because
the rotator cuff receives very little oxygen and nutrients from its
limited blood supply, it is vulnerable to wear and tear.
Degeneration, or general wear and tear, is the result of micro-trauma
from repetitive movements over your lifetime. Gradually the
rotator cuff tendons become frayed. Over time, the rotator cuff
becomes weaker and less able to do it job of positioning the humeral
head during arm movements. Muscular weakness will allow the
humeral head to move up when you raise your arm about your
shoulder. This causes the rotator cuff to get pinched under the
roof which can, over time, lead to tears. This migration is
sometimes evident on x-rays. A diminished blood supply is also
the reason why a shoulder injury can take a long time to heal.
Excessive force, or simply putting too much strain on the tendons of
the shoulder muscles is the second cause of rotator cuff
injuries. This usually occurs when you try to lift or move
something that is too heavy. Additionally, an injury can occur
when a force is applied to the arm while it’s in an awkward
position. This can happen when you fall with your arm
outstretched.
Much of the therapy for shoulder injuries is focused on restoring
strength and stamina to the important muscles. However, movement
in the ball-and-socket accounts for only a portion of the total
movement available to the arm. The rest of the movement is a
result of the shoulder blade moving on your rib cage.
Positioning and control of the socket is dependent on the scapular
stabilizers and good posture. If the shoulder blade is not well
controlled, shoulder pain can result. Therefore, therapy also
includes retraining scapular stabilizers and focusing on good
posture.
