SHOULDER ANATOMY

BONY ANATOMY

Humerus

• proximal end articulates with scapula to from shoulder

• distal end articulates with bones of the forearm to form elbow

Scapula• the shoulder blade

Glenoid fossa has ring of cartilage called labrum to deepen the articular surface

• the glenoid fossa of the scapula articulates with the humerus to form the glenohumeral joint (shoulder)

• the acromion process articulates with the clavicle to from the acromioclavicular joint (tip of the shoulder)

Clavicle

• distally articulates with the acromion process to form the AC joint

• Proximally articulates with the sternum to form SC joint

Review of Joints• Glenoid fossa+humerus=glenohumeral joint (GH)

(scapula)• Acromion process + clavicle =acromioclavicular

(scapula) (AC)• Sternum + clavicle=sternoclavicular (SC)• Scapula+rib cage= scapulothoracic articulation

MUSCLATURE

Trapezius• large, triangular muscle

• starts at base of skull, runs out to tip of shoulder and down to the 12th thoracic vertebrae

• functions to shrug and square the shoulders

Rhomboids• group of two muscles that run diagonally from the spine to the medial border of the scapula

• they function to retract the scapula

Latissimus Dorsi• the “lats”

• gives wing like appearance to sides

• starts along the thoracic vertebrae of back and inserts on the anterior aspect of humerus

• functions extend , adduct and medially rotate the arm

Pectoralis Major• the chest muscle

• originates along the sternum and clavicle, inserts on the humerus

• it functions to:

~ adduct

~ flex

~medially rotate

the arm.

Deltoid• the muslce that gives contour to the shoulder

• originates along the spine of the scapula and clavicle, inserts on the humerus

• all fibers abduct the arm

• anterior fibers: flex and medially rotate arm

• posterior fibers: extend and laterally rotate arm

Biceps• the “popeye” muscle

• on anterior aspect of arm

• crosses both the shoulder and elbow

• flexes the arm

Triceps• on the posterior aspect of the arm

• crosses both the shoulder and elbow

• extends the arm

Rotator Cuff• Group of four muscles

that act to hold the head of the humerus into the glenoid fossa– Supraspinatus– Infraspinatus– Teres Minor– Subscapularis

Rotator Cuff cont.

• Supraspinatus: 1st 10 degrees of abduction• Infraspinatus: external rotation• Teres minor: external rotation• Subscapularis: internal rotation

** Note that there are no muscles on the inferior aspect of the shoulder!! This will be important when we talk about shoulder injuries

Labrum• Ring of cartilage similar to the menisci of

the knee. • Deepens the articular surface of the genoid

fossa and adds to the stability of the shoulder