FEATURE
SHOULDER INJURIES IN Throwing and
Swimming
Mark G. Smith, MD
T
he shoulder has the widest range
of motion of any joint in the hu-
man body. The shoulder’s primary
function is to place the hand in
space. The motion of the shoul-
der requires a concerted action between the
sternoclavicular, acromioclavicular, scapu-
lothoracic and glenohumeral joints.
In sport, the shoulder functions to transmit force from the low-
er body and core to the hand. This can take the form of throwing
projectiles or creating propulsion of the athlete. These activities
place the static and dynamic stabilizers of the glenohumeral joint
under tremendous stress.
The glenohumeral joint is statically stabilized by the convex
concave joint architecture deepened by the labrum. At end range,
the glenohumeral ligaments stabilize the joint. Dynamically in the
middle range, the glenohumeral joint is stabilized by the contraction
of rotator cuff compressing the humeral head in the glenoid. The
long head bicep stabilizes the joint during the throwing motion.
The pectoralis major, latissimus dorsi and deltoid are the primary
movers of the humerus.
During pitching, peak angular velocities of internal rotation
reach 6,180 degrees per second during acceleration. The shoulder
is particularly vulnerable to injury in the late cocking and early
acceleration phase of pitching. During this phase, the anterior
capsule and ligaments are under stretch, leading to increased laxity.
The greater tuberosity of the humerus with the attached posterior
superior rotator cuff contacts the posterior superior glenoid rim and
labrum, creating internal impingement. The long head bicep anchor
also contracts, adding shear forces to the posterior superior labrum.
With overuse and fatigue, injury occurs to the posterior su-
perior labrum and bicep, resulting in superior labrum anterior to
posterior tears. The rotator cuff suffers primarily undersurface tears
(continued on page 18)
APRIL 2019
17