The shoulder joint is the most commonly dislocated of all joints.1–4 Shoulder
dislocations were depicted in Egyptian murals as early as 3000 b.c.1 Despite 5000 years of
medical advancements, shoulder dislocations continue to be a major
cause of Emergency Department visits. They account for more than
50 percent of all joint complications treated by Emergency Physicians.2
The human shoulder is remarkable for its degree of motion. The
anatomic features that contribute to this mobility also contribute
to its instability.3 The shallow glenohumeral joint allows
the shoulder to be dislocated anteriorly, posteriorly, or inferiorly.
The anterior shoulder dislocation is the most common and accounts
for 95 percent of all shoulder dislocations.1–4 The
overall incidence of shoulder dislocations is 17 per 100,000. There
is a bimodal age distribution.1,4 It occurs in males from
20 to 30 years of age most commonly related to athletics and trauma.
The other large group is women from 60 to 80 years of age, primarily
due to falls.
The shoulder (glenohumeral) joint is a multiaxial ball-and-socket
type of synovial joint that permits a wide range of motion. Unfortunately,
the range of motion is at the expense of stability.5 The
shoulder has greater than 180 degrees of motion in both the sagittal
and coronal planes as well as 180 degrees of rotary movement.6 The
spheroidal head of the humerus articulates with the shallow glenoid
fossa of the scapula. The glenoid fossa accommodates roughly one-third
of the humeral head. The bony landmarks surrounding the shoulder
joint are the coracoid and acromion processes of the scapula. A
loose, thin fibrous capsule encloses the glenohumeral joint. The
muscular component of the shoulder is a fusion of four separate
muscles (supraspinatus, infraspinatus, teres minor, and subscapularis)
that together form the rotator cuff. These muscles have a tendency
to be torn and injured in shoulder dislocations, especially posterior
and inferior dislocations.7 The shoulder receives its blood
supply from the anterior and posterior circumflex humeral arteries.
These arteries are branches of the axillary artery. Innervation
of the shoulder is from branches of the suprascapular, axillary,
and lateral pectoral nerves. The axillary nerve lies at the level
of the humeral neck. When it is dislocated anteriorly, the humeral
head is displaced into the quadrangular space where it may compress
and damage the axillary nerve. This can result in neuropraxia or paralysis
of the deltoid muscle and sensory loss to the skin over the shoulder.
Shoulder dislocations can occur anteriorly, posteriorly, or inferiorly
depending on the mechanism of injury. Anterior shoulder dislocations
are by far the most common and account for 95 percent of all dislocations.
An anterior dislocation usually results from direct or indirect
forces causing abduction, extension, and external rotation of the
limb. Anterior dislocations are classified based on the location
of the humeral head into subcoracoid, subglenoid, subclavicular,
and intrathoracic. Subcoracoid dislocations account for 75 percent
of all anterior shoulder ...