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Acromioclavicular (AC) joint - Coggle Diagram
Acromioclavicular (AC) joint
Articular surfaces
consists of the articulation betw
the lateral end of the clavicle
& a small facet on the acromion of the scapula
are incongruent
and are inclined vertically
and may vary from individual to individual
the primary function of the acromioclavicular joint
is to allow the scapular to rotate in 3 dimentions
during arm movement so that the upper extremity motion is increased
n scapula remains congruent n stable on the thorax
also allows transmission of forces frm the upper extremity to the clavicle
Acromioclavicular joint disc
The disc varies from individual and within
individual as well
Fibrocartilaginous union by 2 years of age
and later a joint space develops when
mobility of upper extremity increases,
resulting in a “meniscoid” fibrocartilage
remnant
Acromioclavicular Joint
capsule and ligaments
capsule is weak n cannot maintain integrity of the joint without the reinforcement of the superior & inferior acromioclavicular ligaments n the coracoclavicular ligaments
2 Major ligaments
Acromioclavilcuar ligament
(Clavicle to acromion)
Superior/inferior fibers
Prevent dislocation of scapula
Links motion of scapula to the clavicle
Coracoclavilcular ligament
(clavicle to coracoid process)
Conoid ligament (conoid tubercle on clavicle)
Trapezoid ligaments (trapezoid line on clavicle)
Suspend the scapula from clavicle and prevent dislocation
Accessory ligament
Coracoacromial Ligament:
Attaches the
coracoid process to the acromion process
Acromioclavicular motions
3 primary rotary motions
Internal/external rotation
Occurs approximately around a vertical axis
Best imagined as bringing glenoid fossa of
the scapula anteromedially for internal
rotation and posterolaterllay for external
rotation
During protraction the scapula internally
rotate on the AC level and during retraction
the scapula externally rotates
Anterior/posterior tilting
About an axis directed laterally and anteriorly
During elevation the scapula moves in anterior
tilting in relation to the AC
During depression the scapula moves in
posterior tilting in relation to the AC to adjust
itself on the dome-shaped thorax
Upward/downward rotation
Oblique A-P axis approximately
perpendicular to the scapular plane.
During abduction and flexion, the
scapula moves in upward rotation in
relation to acromion about 30 degrees,
During adduction and extension the
scapula moves in downward rotation
relative to the acromion about 30
degrees
Plane synovial joint
Motion occurs around axes that are
oriented
to the plane of scapula rather
than a cardinal plane
3 translatory motions
Medial/lateral translation
Superior/inferior translation
Anterior/posterior translation
Acromioclavicular stress
Susceptible to both trauma and degenerative changes
-Trauma most often occurs during the first 3 decades of life,
Through accidents
While playing contact sports
Fall on the shoulder with the arm adducted
High inferior forces on the acromion will cause trauma to AC joint
Sprain
Subluxation
Dislocation
Degenerative changes is common from second decade of life
-Joint space frequently narrowed by 6th decade of life
-Likely due to small incongruent articular surface and high forces per unit area