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: 1 st 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