An acromioclavicular joint separation,
or AC separation, is a very frequent injury among physically
active people. In this injury the clavicle (collar
bone) separates from the scapula (shoulder blade).
It is commonly caused by a fall directly on the "point"
of the shoulder or a direct blow received in a contact sport. Football
players and cyclists who fall over the handlebars are often subject
to AC separations.
In general, most AC injuries don't
require surgery. There are certain situations, however, in which
surgery may be necessary. Most patients recover with full function
of the shoulder. The period of disability and discomfort ranges
from a few days to 12 weeks depending on the severity of the separation.
Disruption of the AC joint results in pain and instability in
the entire shoulder and arm. The pain is most severe when the
patient attempts overhead movements or tries to sleep on the affected
The shoulder is the
most mobile joint in the human body, with a complex arrangement
of structures working together to provide the movement necessary
for daily life. Unfortunately, this great mobility comes at the
expense of stability. Four bones and a network of soft tissue structures
(ligaments, tendons, and muscles), work together to produce shoulder
movement. They interact to keep the joint in place while it moves
through extreme ranges of motion. Each of these structures makes
an important contribution to shoulder movement and stability. Certain
work or sports activities can put great demands upon the shoulder,
and injury can occur when the limits of movement are exceeded and/or
the individual structures are overloaded.
is an AC joint separation?
AC joint separation, often called a shoulder separation, is a dislocation
of the clavicle from the acromion. This injury is usually caused
by a blow to the shoulder, or a fall in which the individual lands
directly on the shoulder or an outstretched arm. AC joint separations
are most common in contact sports, such as football and hockey.
The severity of an acromioclavicular
joint injury depends on which supporting structures are damaged,
and the extent of that damage. Tearing of the acromioclavicular
ligament alone is not a serious injury, but when the coracoclavicular
ligaments are ruptured, the whole shoulder unit is involved, thus
complicating the dislocation.
Simple AC injuries are classified in three grades ranging from a
mild dislocation to a complete separation:
|Grade I - A
slight displacement of the joint. The acromioclavicular ligament
may be stretched or partially torn. This is the most common
type of injury to the AC joint.
|Grade II -
A partial dislocation of the joint in which there may be some
displacement that may not be obvious during a physical examination.
The acromioclavicular ligament is completely torn, while the
coracoclavicular ligaments remain intact.
|Grade III -
A complete separation of the joint. The acromioclavicular ligament,
the coracoclavicular ligaments, and the capsule surrounding
the joint are torn. Usually, the displacement is obvious on
clinical exam. Without any ligament support, the shoulder falls
under the weight of the arm and the clavicle is pushed up, causing
a bump on the shoulder.
There are a total of six grades of
severity of AC separations. Grades I-III are the most common. Grades
IV-VI are very uncommon and are usually the result of a very high-energy
injury such as one that might occur in a motor vehicle accident.
Grades IV-VI are all treated surgically because of the severe disruption
of all the ligamentous support for the arm and shoulder.