ESS 303 – Biomechanics Shoulder Joint

The Scapula (Right)

Humerus (Right) Anterior View Posterior View

The Shoulder Joint Shallow ball-and-socket Socket: Glenoid fossa of the shoulder blade Ball: ½ the spherical head of the humerus No more than ½ of the head is in the socket at any given time Bony stability is weak In fact – the head may move up to 2-3 cm away from the glenoid fossa

Stability Keeping the humoral head in contact with the glenoid fossa Passive: Glenoid Labrum Circles around the outside of the glenoid cavity Increases depth of concavity Active: Rotator cuff

Rotator Cuff Muscles tense to stabilize the humoral head against the glenoid fossa Helps prevent the head from rotating out of the fossa Allows the deltoid to contribute to abduction 4 muscles: supraspinatus, subscapularis, infraspinatus, and teres minor

Rotator Cuff Injuries: Common Types: Tendonitis, bursitis, strain or tear Who: Baseball pitchers & anyone who puts heavy demands on their shoulders Most treated with simple care and exercise Causes: age (>40), poor posture, breaking a fall with your arm, heavy lifting (especially overhead), repetitive stress, others

Rotator Cuff Injuries: Common

Rotator Cuff Injuries: Common Self treatment: Stop the activity – for a few days or until pain stops Ice and heat Medications Exercises Medical treatment Severe or long-lasting (> 1 week) pain, immobile, etc Medications, surgery, etc

Dislocation & Subluxation

Movements & Major Muscles Flexion: pectoralis major (clavicular), anterior deltoid & coracobrcahialis Extension: pectoralis major (sternal), latissimus dorsi & teres major Abduction: middle deltoid & supraspinatus Adduction: pectoralis major (sternal), latissimus dorsi & teres major

Movements & Major Muscles Horizontal (Transverse) Abduction: middle and posterior deltoids, infraspinatus & teres minor Horizontal (Transverse) Adduction: pectoralis major, anterior deltoid, coracobrachialis Medial Rotation: pectoralis major, latissimus dorsi, teres major & subscapularis Lateral Rotation: teres minor, infraspinatus & posterior deltoid Other movements are exaggerations or combinations of above: Hyperextension, Hyperabduction, Hyperadduction & Circumduction