Shoulder Instability
The shoulder
is a ball and socket type of joint
with the ball being about twice the size of the socket. If it were not
for the ligaments, muscles and tendons about the joint, the ball would
constantly slide out of the socket. The socket being small when
compared with the ball allows the shoulder
joint to be capable of a large range of motion. However, the price you
pay for such motion, is the greater potential for the ball to slide out
of place either with tearing of or gradual stretching of structures.
The socket is call the glenoid and the ball the humeral head. top
muscles functions to contain the humeral head as we move our shoulder.
The four muscles that make up the rotator cuff are the supraspinatus,
infraspinatus, teres minor, and subscapularis. These muscles originate
from the scapula and converge to form a cuff to tendon that inserts
into the humeral head. The ligaments about the shoulder converge with
the shoulder capsule to contain the humeral head.
A sudden forceful injury can tear the ligaments and capsule and cause
the humeral head to slide out of the glenoid resulting in a
dislocation. Sever pain usually results from a dislocation and
persists until the shoulder joint is reduced. After a dislocation,
the ligaments and capsule
rarely regain their original shape and strength and shoulder dislocates
with less force in the future.
Younger people have a greater propensity to dislocate again than older people because of their greater activity level. In some cases a forceful dislocation does not occur but the ligaments and capsule become stretched out over a period of time. When this happens, the humeral head does not completely dislocate from the joint, but partially slides out of place or subluxes which causes pain with certain activities, such as throwing or climbing.
