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Shoulder (glenohumeral) joint

Type

Shoulder cross-section.png

Synovial, ball and socket

Multiaxial

Widest range of movement (ROM) at cost of stability

Articulating surfaces:

Glenoid fossa (scapula) – shallow

Head of humerus – large, spherical

Articulating surfaces lined with hyaline cartilage

Cartilage: glenoid labrum

Attached to margin of glenoid fossa to deepen and expand fossa

Synovial membrane

Shoulder capsule.png

Attaches to margins of articular surfaces and lines joint capsule

Loose inferiorly to allow for abduction

Bursae

Protrusions of synovial membrane enclosing synovial fluid
Subscapularis bursa lies between subscapularis muscle and joint capsule

Capsule

Somewhat loose, allowing for extensive ROM

Attaches to:

Scapula: margins of glenoid fossa enclosing glenoid labrum

Humerus: anatomical neck extending to surgical neck medially

Ligaments

Glenohumeral ligament: glenoid margin to anatomical neck

Coracohumeral ligament: coracoid process (scapula) to lesser tubercle (humerus)

Transverse humeral ligament: bridges intertubercular groove, not really contributing to joint stability

Movements

Flexion-extension, abduction-adduction, medial & lateral rotation, circumduction

Clinical

Frequently dislocated (usually anteroinferiorly) due to lack of bone stability and wide ROM

Stabilising factors

Rotator cuff muscles

Tendons blend with joint capsule, form cuff anteriorly, superiorly, posteriorly
Cuff holds head of humerus in glenoid cavity without compromising ROM

Long head of biceps

Passes superiorly through joint
Restricts upward movement of head

Ligaments and coracoacromial arch

Axilla (aka armpit)

Shoulder-scapula.png

Pyramidal space between arm and thoracic wall

Passage for blood vessels and nerves to reach upper limb

Boundaries

Anterior wall: Pectoralis major and pectoralis minor muscles

Posterior wall: Teres major and subscapularis muscles

Medial wall: Serratus anterior muscle, thoracic wall

Lateral wall: Humerus (intertubercular groove)

Contents

Axillary artery and axillary vein and their branches

Nerves (cords of brachial plexus and its branches)

Muscles of Shoulder and Arm

Rotator cuff of muscles

Muscle Origin Insertion Innervation Action
Supraspinatus Supraspinous fossa Humerus (greater tubercle) Suprascapular nerve Stabilises shoulder, abduction
Infraspinatus Infraspinous fossa Humerus (greater tubercle) Suprascapular nerve Stabilises shoulder, lat rotation
Teres minor Lateral border of scapula Humerus (greater tubercle) Axillary nerve Stabilises shoulder, lat rotation
Subscapularis Subscapular fossa Humerus (lesser tubercle) Subscapular nerve Strongest RC muscles, medially rotates humerus

Upper limb of vertebral column

Muscle Origin Insertion Innervation Action
Trapezius Superior nuchal line, ext occipital protub., lig nuchae, spinous processes of C7-T12 Clavicle (lat 3rd), scapula (acromion & spine) Accessory nerve (CnXl), C3&C4 Assists in rotating scapula during abduction of humerus above horizontal. Elevate, adducts and lower fibres depress scapula
Lattismus dorsi Spinous processes of T6 to sacrum, iliac crest, scapula Humerus (intertubercular sulcus) Thoracodorsal nerve Extends and medially rotates humerus

Upper limb to thoracic wall

Muscle Origin Insertion Innervation Action
Pectoralis maj Clavicle, sternum, costal cartilages 2-6 Humerus (lat lip) Med and lat pectoral nerves Flexion, adduction and medial rotation of arm
Pectoralis min Ribs 3-5 Scapula (corocoid process) Med and lat pectoral nerves Protraction/depression of scapula
Serratus ant 8 slips from upper 8 ribs Scapula (medial border of ant surface) Long thoracic nerve Protraction/rotation of scapula

Upper limb to scapula

Muscle Origin Insertion Innervation Action
Deltoid Scapula (spine and acromion), clavicle (lat 3rd) Humerus (deltoid tuberoscity) Axillary nerve Major abductor of arm (further than initial 15˚ done by supraspinatus), all other movements
Teres major Scapula (lat border) Humerus (medial lip) Subscapular nerve Extension, medial rotation, assists in adduction
Biceps brachii Scapula: long head- supraglenoid tubercle, short head- corocoid process Tendon on radial tuberoscity, aponeurosis Musculocutaneous n Flexes forearm, supinates forearm, flexes arm
Triceps brachii Long head- scapula, med and lat heads- post humerus Common tendon of insertion olecranon of ulna Radial nerve Extension, long head also adducts

Other

Muscle Origin Insertion Innervation Action
Brachialis Humerus (dist half) Coronoid process of ulna Musculocutaneous nerve Flexes forearm