Acromioclavicular Joint
What motions occur at AC joint?
1) Internal/External Rotation 2) Upward/Downward Rotation 3) Anterior/Posterior Tilt
What are the ligaments of the AC joint (that make up the capsule)?
1) Superior Acromioclavicular ligament 2) Inferior Acromioclavicular Ligament 3) Coracoclavicular ligament *Conoid ligament *Trapezoid ligament 4) Coracoacromial ligament
Internal/External Rotation
brings the vertebral border of the scapula closer to (external rotation) or farther from (internal rotation) the clavicle in the transverse plane
What type of cartilage covers the AC Joint?
fibrocartilage (NOT hyaline)
What is the shape of the acromioclavicular joint?
flat articular surfaces
The AC joint is what type of joint?
gliding joint = synovial joint
Why is the trapezoid ligament the most important ligament of the AC joint?
great question! look it up. JK (I'm hilarious), The more obliquely aligned Trapezoid Ligament protects against shearing forces that can drive the acromion inferiorly and medially under the clavicle ... stops movement of the scapula
Upward/Downward Rotation
results in enlarging or shrinking the angle formed by the clavicle and spine of the scapula in the frontal plane
Trapezoid Ligament
runs vertically and laterally to the trapezoid line (most important ligament of the AC joint) • The more obliquely aligned Trapezoid Ligament protects against shearing forces that can drive the acromion inferiorly and medially under the clavicle ... stops movement of the scapula
In what axis does upward/downward rotation occur?
the anterior/posterior axis
In what axis does anterior/posterior tilt occur?
the mediolateral axis (ML axis)
If something is a synovial joint, what does that automatically tell you?
this automatically tells us this has a capsular ligament
Anterior/Posterior Tilting
tilts the superior border of the scapula toward the clavicle (anterior tilting) or away from it (posterior tilting)
In what axis does internal/external rotation occur?
vertical axis
What can happen to the AC joint if you fall on your shoulder?
when you fall on your shoulder, it wants to push acromion medially, which can cause it to slide under clavicle... can cause permanent deformation
In terms of excursions, how far can the AC joint move anteriorly/posteriorly and superiorly/inferiorly?
~4 mm in the anterior/posterior directions ~2 mm in the superior/inferior directions
Coracoacromial Ligament
• Does not cross any joint • Attaches from the acromion process to the coracoid process forming a roof over the humeral head • Acts to provide protection for the underlying bursa and supraspinatus tendon • Provides a limit to the superior gliding of the humerus in a very unstable GH joint
Coracoclavicular Ligament (what type of ligament, where does it run from, function, what 2 parts is it composed of)
• Extracapsular ligament • Runs from the base of the coracoid process to the inferior surface of the clavicle (conoid tubercle and trapezoid line) • Provides support against large excursions and medial displacements • Regarded as the primary suspensory ligament of the shoulder complex • Composed of two parts: the Conoid Ligament and the Trapezoid Ligament
Capsule of the AC Joint
• Frequently described as weak • The AC Ligaments provide the primary support to the joint in instances of small displacements and low loads
Superior Acromioclavicular Ligament
• Provide important limitations to posterior glide of the lateral end of the clavicle on the acromion
Inferior Acromioclavicular Ligament
• Provide important limitations to posterior glide of the lateral end of the clavicle on the acromion • May also provide substantial resistance to excessive anterior displacement of the clavicle on the acromion
Conoid Ligament
• Runs vertically from the coracoid process to the conoid tubercle on the clavicle • Vertically aligned Conoid Ligament limits excessive superior glides of the lateral end of the clavicle on the acromion
