Acromioclavicular Joint

Question 1

Type of Joint

Answer 1

Synovial plane between clavicle and acromion process of scapular capable of small gliding movements of acromion on clavicle

• about vert axis=protraction/retraction
• about sag axis=elevation/depression
• axial rotation=med/lat scapula rotation through conoid ligt

Question 2

Articular Surfaces

Answer 2

Flat oval art.surfs on lat end of clavicle and anteromedial border acromion
Both surfaces covered in fibrocartilage

Clavicle surfaces face posterolaterally, acromial face anteromedially

Question 3

Supporting Ligaments

Answer 3

Coracoclavicular- lat end of clavicle to coracoid process

• prevents med displacement of acromion under lat end of clavicle in lat directed forces to shoulder
• Conoid part=most med, limits forward movement
• Trapezoid part=most lat, limits backward movement

Acromioclavicular- acromion to clavicle
-reinforces joint capsule

Question 4

Capsule Info

Answer 4

Is weak and strengthened by AC ligts inferiorly and superiorly
-these are reinforced through attachments from deltoid and trapezius

Synovial membrane lines all non-articular surfaces
Partial fibrocartilaginous disc attaches to sup capsule

Question 5

Functions

Answer 5

• Allow scapula additional range of rotation on the thorax
• Allow for adjustments of scapula (tipping, int/ext rot) outside initial plane of scapula to follow the changing shape of thorax as arm moves
• Allows transmission of forces from the upper extremity to the clavicle.

Question 6

Common injuries

-joint sprain

Answer 6

Type 1- stretched ligt
Type 2- partial rupture of AC ligts
Type 3- complete rupture of AC and CC ligts
Type 4- clavicle displaced post over acromion
Type 5- clavicle displaced just under skin
Type 6 (v rare)- clavicle displaced under coracoid process