ESS 303 – Biomechanics

Shoulder Joint

The Scapula (Right)

Humerus (Right)

Anterior View Posterior View

The Shoulder Joint

Shallow ball-and-socketSocket: Glenoid fossa of the shoulder bladeBall: ½ the spherical head of the humerusNo more than ½ of the head is in the socket

at any given timeBony 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 LabrumCircles 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 tearWho: Baseball pitchers & anyone who

puts heavy demands on their shouldersMost treated with simple care and

exerciseCauses: 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