Shoulder - Chapter 3, Biomechanics

The shoulder consists of what two parts?

Shoulder girdle and shoulder joint

What bones make up the shoulder girdle?

Clavicle and scapula

What bones make up the shoulder (glenohumeral) joint?

Scapula and humerus

Where does the clavicle attach?

Medially to the sternum and laterally to the scapula

What is unique about the clavicle?

Only bony attachment of the shoulder trunk

Why is the clavicle commonly fractured?

Because of its shape and little protection

What is the lateral end of the clavicle called?

Acromial end

What is the medial end of the clavicle called?

Sternal end

Name the major bony landmarks of the clavicle

Deltoid tubercle, conoid tubercle, trapezoid line, costal tuberosity, subclavian groove

What is another name for the scapula?

Shoulder blade

The scapula is considered part of what structures?

Both shoulder girdle and shoulder joint

What are the borders and angle of the scapula?

Medial border, lateral border, and inferior angle

What is found on the superior border of the scapula?

Scapular notch

Which process is anterior on the scapula?

Coracoid process

Which process is posterior on the scapula?

Acromion process

What forms the shoulder socket?

Glenoid fossa

What tubercle is above the glenoid fossa?

Supraglenoid tubercle

What tubercle is below the glenoid fossa?

Infraglenoid tubercle

What is the smooth anterior surface of the scapula called?

Subscapular fossa

What are the two fossae on the posterior surface?

Supraspinous fossa and infraspinous fossa

What is another name for the shoulder joint?

Glenohumeral joint

What type of joint is the shoulder joint?

Ball-and-socket joint

What forms the socket?

Glenoid fossa

What forms the ball?

Head of the humerus

Where is the anatomical neck of the humerus?

Between head of humerus and greater and lesser tuberosities

Where is the surgical neck?

Upper portion of the humeral shaft

How many facets does the lesser tuberosity have?

One

How many facets does the greater tuberosity have?

Three (proximal, middle, distal)

What is the bony prominence halfway down the lateral humerus?

Deltoid tuberosity

What are the two joints of the shoulder girdle?

Acromioclavicular (AC) joint and sternoclavicular (SC) joint

What type of movement occurs at the SC joint?

Slight gliding and rotational movements

What provides stability to the SC joint?

Clavicular notch and ligamentous arrangement

What are the three primary ligaments of the SC joint?

Sternoclavicular, costoclavicular, and interclavicular ligaments

What does the sternoclavicular ligament contain?

Anterior, superior, and posterior fibers

What does the costoclavicular ligament connect?

Sternal end of clavicle to the first rib

What does the interclavicular ligament connect?

Sternal ends of both clavicles across manubrium

Where is the articular disc located?

Between sternal end of clavicle and clavicular notch of manubrium

What does the acromioclavicular ligament connect?

Lateral clavicle to acromion process

What are the four fundamental movements of the shoulder girdle?

Elevation, depression, abduction, and adduction

What is elevation?

Superior movement of scapula

What is depression?

Inferior movement of scapula

What is shoulder girdle abduction?

Upward rotation and lateral tilt of scapula

What is shoulder girdle adduction?

Downward rotation and medial tilt of scapula

What is protraction?

Scapulae tilt laterally as they glide around the chest

What is retraction?

Scapulae tilt medially as they glide around the chest

What are the anterior shoulder girdle muscles?

Pectoralis minor, serratus anterior, and subclavius

Where does the pectoralis minor originate and insert?

Origin: 3rd-5th ribs; insertion: coracoid process

What is the action of pectoralis minor?

Pulls coracoid process toward ribs

Where does serratus anterior originate and insert?

Origin: first 9 ribs; insertion: anterior surface of vertebral border of scapula

What is the action of serratus anterior?

Abduction (protraction) of shoulder girdle

Where does subclavius originate and insert?

Origin: 1st rib; insertion: subclavian groove

What is the function of subclavius?

Stabilizes sternoclavicular joint

What are the three posterior shoulder girdle muscles?

Levator scapulae, rhomboids, trapezius

What is the action of levator scapulae?

Elevates scapula

What is the action of the rhomboids?

Elevation and adduction (retraction)

What are the actions of the trapezius?

Upper fibers: elevation and adduction; middle fibers: adduction; lower fibers: abduction (upward rotation)

Where does levator scapulae originate and insert?

Originate: transverse process of 1st 4 cervical vertebrae; insertion: superior aspect of vertebral border of scapula

Where do the rhomboids originate and insert?

Originate: spinous process of 7th cervical through 5th thoracic vertebra; insertion: vertebral border of spine

Where does the trapezius originate and insert?

Originate: external occipital protuberance; insertion: spine of scapula and posterior surface of clavicle

What is flexion?

Anterior movement of arm

What is extension?

Posterior movement of arm

What is abduction?

Movement away from body’s midline

What is adduction?

Movement toward body’s midline

What is circumduction?

Combination of shoulder’s fundamental movements

What are the 4 anterior muscles of the shoulder joint?

Pectoralis major, coracobrachialis, biceps brachii, subscapularis

Where does the pectoralis major originate and insert?

Origin: 2nd to 6th ribs, sternum, and medial half of clavicle; insertion: anterior area of surgical neck of humerus

Where does the coracobrachialis originate and insert?

Origin: Coracoid process; insertion: middle of medial side of humerus

Where does the biceps brachii originate and insert?

Origin: supraglenoid tubercles on superior edge of glenoid (long head) and coracoid process (short head); insertion: heads combine on tuberosity of radius

Where does the subscapularis originate and insert?

Origin: large scapular fossa on anterior side of scapula; insertion: lesser tuberosity of humerus

What are the actions of coracobrachialis?

Flexion and assists with adduction

What are the actions of biceps brachii?

Flexion, abduction, and internal rotation

What are the actions of subscapularis?

Internal rotation and flexion

Which rotator cuff muscle is on the anterior side?

Subscapularis

What are the two posterior muscles of the shoulder joint?

Infraspinatus and teres minor

Where does the infraspinatus insert?

Middle facet of greater tuberosity

Where does infraspinatus originate?

Infraspinous fossa beneath inferior surface

What are the actions of infraspinatus?

External rotation and extension

Is infraspinatus apart of the rotator cuff?

Yes

Where does teres minor insert?

Distal facet of greater tuberosity

Where does teres minor originate?

Upper and middle portions of lateral border

What are the actions of teres minor?

External rotation and extension

Is teres minor part of the rotator cuff?

Yes

What are the 2 superior muscles of the shoulder joint?

Deltoid and supraspinatus

Where does the supraspinatus originate?

Supraspinous fossa of scapula

Where does the supraspinatus insert?

Proximal facet of greater tuberosity

What is the primary action of the supraspinatus?

Initiates shoulder abduction (first 30 degrees)

Is supraspinatus part of the rotator cuff?

Yes

What muscle consists of anterior, middle, and posterior portions?

Deltoid muscle

Where does the anterior deltoid originate?

Lateral portion of anterior aspect of clavicle

Where does the middle deltoid originate?

Lateral edge of acromion process

Where does the posterior deltoid originate?

Inferior edge of spine of scapula

Where does the deltoid insert?

Deltoid tubercle on lateral surface of middle humerus

What is the primary action of the entire deltoid muscle?

Abduction of shoulder

What are the actions of the posterior deltoid?

Adduction, extension, and external rotation

What are the actions of the anterior deltoid?

Adduction, flexion, and internal rotation

What are the inferior muscles of the shoulder joint?

Latissimus dorsi, teres major, and triceps brachii (long head)

This is the origin of what muscle?

Lower 6 thoracic vertebrae, all 5 lumbar vertebrae, posterior ilium, lower 3 ribs, and inferior angle of the scapula

Latissimus dorsi

Where does latissimus dorsi insert?

Edge of intertubercular groove on anterior humerus

What are the actions of latissimus dorsi?

Internal rotation, extension, and adduction

Where does the teres major originate?

Lower lateral border and inferior angle of scapula