SC Joint
Proximal clavicle, manubrium, and part of the first costal cartilage
Distal clavicle and acromion process
What functional plane of motion is formed by the ST articulation?
Scapular plane
Flexion/extension
Abduction/adduction
Internal/external rotation
List origin, insertion, and action of the supraspinatus muscle
O: Supraspinous fossa of the scapula
I: Medial aspect of the greater tuberosity of the humerus; glenohumeral joint capsule
A: Abduction and external rotation of the humerus; humeral head stabilization
What are the 4 ligaments of the SC joint?
Anterior sternoclavicular
Posterior sternoclavicular
Costoclavicular
Interclavicular
What type of joint is the AC joint?
Plane synovial joint
Why is the ST articulation not considered a true joint?
It lacks connection by fibrous, cartilaginous, or synovial tissues
What is the structure that increases the depth of the glenoid fossa?
Glenoid labrum
List origin, insertion, and action of the teres minor.
O: Lateral upper 2/3 of the axillary border of the scapula
I: Lateral aspect of the greater tuberosity
A: External rotation and horizontal abduction of the humerus
What are the three degrees of freedom of the SC Joint?
Protraction/retraction
Elevation/depression
Internal/external rotation
What are the 2 main ligaments of the AC joint?
Acromioclavicular ligament
Coracoclavicular ligament
ST articulation allows what 4 motions to occur?
Anterior/posterior tilt
Upward/downward rotation
Retraction/protraction
Elevation/depression
Which ligament limits inferior translation of the humeral head when the arm is hanging at the side
Coracohumeral ligament
What is the angle of inclination? What is considered a normal angle of inclination?
Axis through the humeral head and neck in relation to an axis through the shaft of the humerus. Normal is 130 - 150 degrees
What ligament resists posterior displacement of the clavicle?
Anterior sternoclavicular ligament
What are the 3 degrees of freedom of the AC joint?
Internal/external rotation around a vertical axis
Upward/downward rotation around an axis perpendicular to the scapular plane
Anterior/posterior scapular tipping around a horizontal axis
What is the ratio between GH elevation and scapular rotation that allows full abduction ROM to occur?
2:1
What structures protect the superior humeral head, tendons of the rotator cuff muscles, and bursae, and restrains against superior and anterior GH dislocation
Coracoacromial arch and ligament
List origin, insertion, and action of the subscapularis
O: subscapular fossa
I: Lesser tuberosity of the humerus
A: Internal rotation of the humerus; humeral head stabilization
What structure is located in the SC joint cavity and provides additional support to the joint?
Sternoclavicular disk
What are the 2 parts of the coracoclavicular ligament and what do they do?
Trapezoid ligament – limits lateral movement of the clavicle over the acromion
Conoid ligament – restricts superior movement of the clavicle
How many degrees of shoulder abduction can occur in the ST articulation, without motion at the GH joint?
60
List 2 reasons the GH joint is unstable
Small glenoid & large humeral head
Loose joint capsule
Weak ligamentous support
Describe the force couple that occurs during abduction
Early abduction: rotator cuffs angle of pull must be sufficient to hold the humeral head against the glenoid fossa
After 90°: rotator cuff angle of pull changes to slide the humeral head inferiorly on the glenoid & clearance to pass under the acromion process and coracoacromial ligament