Shoulder / Pectoral Girdle Arthrology and Myology Flashcards
What are the 3 joints of the shoulder region?
Acromioclavicular joint
Sternoclavicular joint
Glenohumeral joint
Description of sternoclavicular joint?
Articulation between medial end of clavicle and superolateral angle of manubrium of sternum and adjacent part of 1st costal cartilage: larger clavicular articular surface so that clavicle projects above manubrium.
Surfaces reciprocally concavoconvex but of different radii of curvature: congruence partly improved by fibrocartilaginous intra-articular disc.
Description of acromioclavicular joint?
Flat oval articular surfaces on lateral end of clavicle and anteromedial border of acromion; both surfaces covered with fibrocartilage.
Clavicular surface faces posterolaterally, acromial surface faces anteromedially.
Description of sternoclavicular fibrous capsule?
Strong fibrous capsule attaches to articular margins of clavicle and sternum, extending inferiorly onto the upper surface of 1st costal cartilage.
Reinforced by anterior, posterior and interclavicular ligs.
Complete intra-articular fibrocartilaginos disc attaches to capsule, dividing joint into 2 separate compartments.
Synovial membrane lines each compartment.
What is the extracapsular sternoclavicular ligament and where does it attach?
Costoclavicular ligament:
→ passes from upper surface of 1st costal cartilage to inferior surface to inferior surface of medial end of clavicle.
→ limits elevation of clavicle as well as preventing excessive anterior/posterior movement of it’s medial end.
Description of acromioclavicular fibrous capsule?
Loose fibrous capsule attaches to articular margins.
Reinforced by superior and inferior acromioclavicular ligaments.
Partial fibrocartilaginous disc attaches to superior capsule in most joints.
Synovial membrane lines all non-articular surfaces.
Where is the extracapsular ligament at the ACJ and what is its role?
Coracoclavicular ligament:
Anchors lateral end of clavicle to coracoid process: conoid and trapezoid parts attach to conoid tubercle and trapezoid line respectively.
Conoid part limits forward movement and trapezoid part backward movement of clavicle → both prevent medial displacement of acromion under the lateral end of clavicle in laterally directed forces to the shoulder.
What muscles stabilise the scapula relative to the thorax during movements of the arm?
trapezius
levator scapulae
What do all the fibres of deltoid do?
abduction
What do the anterior fibres of deltoid do?
Flexion and medial rotation
What do the posterior fibres of deltoid do?
Extension and lateral rotation
What is the action of supraspinatus?
Initiates the first 20 degrees of abduction
What is the action of teres minor?
Laterally rotates the glenohumeral joint
What does infraspinatus do?
laterally rotates the glenohumeral joint
What does subscapularis do?
Medially rotates the glenohumeral joint
What does all of pectoralis major do?
Adduction at the GHJ
What do the clavicular fibres of the pectoralis major do?
Flexion at the glenohumeral joint
What do the sternocostal fibres of pectoralis major do?
Extension (from a flexed position) at GHJ
What do the upper fibres of trapezius do?
→ Laterally flex the neck to the same side when working uni-laterally and extend the neck when working bilaterally.
→ Assist in lateral scapula rotation
e.g. looking up at ceiling, resisting depression of SG when carrying bags
What do the middle fibres of trapezius do?
→ Retract the shoulder girdle
e.g. opening door/any pulling activity of the upper limb
What do the lower fibres of trapezius do?
→ Depress the shoulder girdle
→ Assist in lateral scapula rotation
e.g. pushing on arms of chair to help sit to stand
What action does teres minor do?
→ Adduction
→ Extension
→ Medial rotation
(of GHJ)
Powerful extensor of the shoulder when in a position of flexion.
What action does latissimus dorsi do?
→ Adduction
→ Extension
→ Medial rotation
(of GHJ)
Powerful extensor of the shoulder when in a position of flexion.
What actions does serratus anterior allow?
→ Protraction
→ Lateral rotation
What actions does pectoralis minor allow?
→ Protraction
→Medial rotation
What muscles produce lateral rotation of scapula?
Upper fibres trapezius → lifts clavicle and acromion
Lower fibres trapezius → pulls down on medial end of spine of scapula
Serratus anterior → pulls down on the inferior angle
What muscles produce medial rotation of scapula?
Levator scapulae
Rhomboids
Pectoralis minor
Description of glenohumeral joint?
The articular surface is deepened by the presence of the fibrocartilaginous glenoid labrum but remains little more than one-third that of the humeral head.
Irrespective of the position of the joint, only 1/3 of the humeral head is in contact with the glenoid fossa at any one time, giving the joint its wide ROM.
Description of glenohumeral joint capsule?
A loose fibrous capsule completely surrounds the joint attaching to the glenoid labrum on the scapula and to the anatomical neck and articular margin of the humeral head, except inferiorly.
The anterior capsule is thickened by superior, middle and inferior glenohumeral ligaments.
Rotator cuff tendons spread out and blend w/capsule.
Provides little stability to joint.
Tendon of long biceps passes through opening in capsule at the upper end of intertubercular groove.
What muscles abduct the shoulder?
Supraspinatus
Deltoid
What muscles adduct the shoulder?
Coracobrachialis
Pectoralis major
Latissimus dorsi
Teres major
What muscles flex the shoulder?
Pectoralis major
Deltoid (anterior fibres)
Coracobrachialis
What muscles extend the shoulder?
Latissimus dorsi
Teres major
Pectoralis major (to midline)
Deltoid (posterior fibres)
Triceps (long head)
What muscles medially rotate the shoulder?
Subscapularis
Teres major
Latissimus dorsi
Pectoralis major
Deltoid (anterior fibres)
What muscles laterally rotate the shoulder?
Teres minor
Infraspinatus
Deltoid (posterior fibres)
