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Shoulder Anatomy Review



SHOULDER ANATOMY
shoulder girdle = awesomely mobile set of bones, 2 each: clavicles, scapulae, humeri
roof of shoulder is acromion process of scapula

FOUR JOINTS OF THE SHOULDER
1) glenohumeral
ball and socket joint of humeral head and glenoid fossa =
most mobile and also most easily dislocated joint in the body
2) acromioclavicular (AC) connects acromion of scapula with lateral clavicle
connected by a strong ligament that is also sometimes damaged
"AC joint separation"
3) sternoclavicular (SC) joint between clavicl and manubrium near jugular notch
4) scapulothoracic articulation
not really a joint but sheets of fascia and fat where the scapula slides over the thoracic ribs

LIGAMENTS OF THE SHOULDER
acromioclavicular (AC)
coracoacromial (from coracoid process to acromial process, both on scapula)
coracoclavicular (a fan of ligaments holding the clavicle down to the coracoid below)
coracohumeral (another stabilizer)
the shoulder capsule (also ligamentous)
subscapularis tendon
supraspinatus tendon

SPRAINS OF LIGAMENTS
1st degree: a few fibers torn
2nd degree: about half the fibers torn
3rd degree: rupture

STRAINS OF MUSCLES
1st degree: a few fibers torn
2nd: about half
3rd: rupture

GLENOID LABRUM
unique donut-shaped ligament that increases the contact between the ball and socket
from 25% bony contact to 75% contact of the head including the donut
sort of a buffer around the edges

MUSCLES OF THE SHOULDER

ROTATOR CUFF
the four tendons that connect the very deepest shoulder muscles to the humerus
located just outside the joint capsule, these four tendons & associated muscles stabilize the joint
SITS = subscapularis, infraspinatus, teres minor, supraspinatus
this order is important, don't switch the S's

SUBSCAP:
O: ant scapula (underneath the bone on the back, up against the ribs but sliding above them)
I: lesser tuberosity of humerus
N: subscapular, C5-6-7
A: int rot and adduct

INFRASPINATUS
O: inferior posterior scapular (below the spine)
I: greater tuberosity of humerus
N: suprascapular nerve C5-6
A: ext rot and abduct

TERES MINOR
O: lateral inferior posterior scapula, below subscap
I: greater turberosity
N: axillary C5-6
A: ext rot and adduct

SUPRASPINATUS:
O: top of posterior scap
I: greater tuberosity of humerus
N: suprascapular, C4-5-6
A: abduction (only up to shoulder level, then deltoid takes over)

TERES MAJOR IS NOT PART OF THE ROTATOR CUFF
because it is more superficial

BICEPS
O LONG HEAD: supraglenoid tubercle
O SHORT HEAD: coracoid process
I: tuberosity of radius
N: musculocutaneous C5-6
A: forearm supination, elbow flexion

CORACOBRACHIALIS
O: coracoid process (with short head biceps, body of muscle higher)
I: mid humerus
N: musculocutaneous (same as biceps)
A: shoulder flexion and accudtion

PEC MINOR
O: ribs 3-5
I: coracoid
N: medial pectoral C8-T1
A: stabilize scap, pulls it inferior and anterior

DELTOID
most superficial, pads and protects the rest
O: clavicle, acromion, spine of scap
I: deltoid tuberosity of humerus
N: axillary C5-6
A: anterior portion: flex and int rot
middle portion: abduct
posterior portion: extension, external rotation

TRICEPS
O: infraglenoid tubercle, posterior humerus
I: olecranon of ulna
N: radial C6-7-8
A: elbow extension, stabilize humerus

BURSAE OF SHOULDER

SUBACROMIAL
under acromion, coracoid, AC joint, coracoacromial ligament
lubes the rotator cuff
aka subdeltoid, spreads out under there
ROTATOR CUFF INJURY MECHANISMS
excessive stretch
postural overload
violent contraction
direct trauma

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