Elevation/Depression

Protraction/Retraction

Internal/external rotation

Anterior/posterior tiping

Static stabilization of the GH Due to incongruence of the GH articular surfaces, the bony surfaces alone cannot maintain joint contact in dependent position (arm hanging at the side). LOG pull the humeral head inferiorly it need an equal upward pull to stabilize, such an upward pull is could be supplied by muscles such as deltoid, supraspinatus, and long head of biceps but the EMG shows these muscle are electrically silent, thus the stabilization in this dependent position is passive, the superior capsule, SGHL, CH ligament, are taut during relaxed dependent position. The resultant pull of LOG and these structure create a force which compresses the head in Glenoid fossa Healthy GH joint is seal by labrum and capsule, any translation produces a negative pressure that resist the inferior translation. Any tear in labrum thus results in

Static stabilization of the GH Degree of Glenoid inclination also play a role in static stability , if there is upward inclination either structurally or by upward scapular rotation will resist more inferior translation of the humeral head. If the arm is loaded then the passive restraints are inadequate to resist the translation then the supraspinatus is recruited because the supraspinatus is attached on the capsular structures, paralysis of the supraspinatus causes inferior subluxation of the humeral head due to sustained forces which causes the capsule to b e lax.

Dynamic stabilization of GH The deltoid and GH stabilization Generally deltoid is considered as prime mover for flexion and abduction however the resultant action of the deltoid muscle is used in stabilization of the GH joint during elevation

The RC and GH stabilization The supraspinatus, infraspinatus, teres minor, and subscapularis muscles compose the rotator or musculotendinous cuff (also referred to by the acronym SITS muscles) These muscles are the GH joint compressor during elevation, these muscles and deltoid muscle make force couple

The supraspinatus and GH stabilization Unlike other RC muscles the suprspinatus has a superior translatory component rather than inferior component that’s why can,t offset the superior translation of the deltiod. However the supraspinatus muscles rotatory component is larger than that of other RC muscles The supraspinatus has a large moment arm that is capable of independently producing abduction full range of GH joint simultaneously stabilizing it Gravity also paly in stabilizing by offsetting the upward pull of the supraspinatus and deltoid muscles

The long head of bicep and GH stabilization The long head of the biceps brachii runs superiorly from the anterior shaft of the humerus through the bicipital groove between the greater and lesser tubercles to attach to the supraglenoid tubercle and superior labrum. It enters the GH joint capsule through an opening between the supraspinatus and subscapularis muscles, where it penetrates the capsule but not the synovium The long head of the biceps brachii, because of its position at the superior capsule and its connections to structures of the rotator interval capsule to be part of the reinforcing cuff of the GH jointThe biceps muscle is capable of contributing to the force of flexion and can, if the humerus is laterally rotated, contribute to the force of abduction and anterior stabilization.

Pairing of Pec Girdle and Shoulder Joint Movements Shoulder Jt Shoulder Girdle Abduction Upward rotation Adduction Downward rotation Flexion Elevation / upward rotation Extension Depression / downward rotation Internal rotation Abduction (protraction) External rotation Adduction (retraction) Horizontal abduction Horizontal adduction

Orientation Muscles of the Pectoral Girdle Muscles of the thorax that move the pectoral girdle Anterior thoracic muscles Posterior thoracic muscles Muscles of the thorax that move the humerus. Axial muscles that move the humerus Scapular muscles that move the humerus.

Muscles of the Thorax Move the Pectoral Girdle Anterior thoracic muscles Subclavius Pectoralis minor Serratus anterior Posterior thoracic muscles Fiber of trapezius Levator scapulae Rhomboid minor Rhomboid major

Muscles of the Thorax that Move the Humerus Axial muscles Pectoralis major Latissumus dorsi Scapular muscles Fiber of deltoid Rotator cuff Teres major Coracobrachalis Long & short head of biceps Long head of triceps

ORIGIN, INSERTION, ACTIONS AND NERVE SUPPLY

Subclavius Muscle Subclavius Origin – 1st rib Insertion – lower surface of clavicle Action Depression and move clavicle anteriorly Helps stabilize pectoral girdle Nerve supply Subclavian nerve Subclavius

Pectoralis Minor Origin 2nd - 5th ribs, 3rd – 5th ribs or 2nd – 4th ribs. Insertion Coracoid process of scapula Action Abduction scapula and rotates it downward Elevate the ribs during forced inhalation. Nerve supply Medial pectoral nerve

Pectoralis Minor

Serratus Anterior Origin – Superior 8 or 9 ribs Insertion – vertebral border and inferior angle of scapula Action Abduction and rotates the scapula upward Elevate ribs when scapula stabilized. Also known as “boxer’s muscles” Nerve supply Long thoracic nerve

Fiber of Trapezius Consists 3 fibers Superior or upper fiber, middle fiber and inferior or lower fiber. Important for move the scapula. Nerve supply - accessory nerve and cervical spinal nerve.

Upper / Superior Fiber of Trapezius Origin – medial one third of the superior nuchal line, external occipital protuberance and ligamentum nuchae. Insertion – posterior border of the lateral one third of the clavicle. Action – scapular elevation

Middle Fiber of Trapezius Origin – spinous process of T1 – T5 Insertion – medial border of the acromion process of scapula, and superior border of the spine of the scapula. Action – scapular adduction.

Lower / Inferior Fiber of Trapezius Origin – spinous process of T6-T12 Insertion – spine of the scapula Action scapular depression and adduction

Levator Scapulae Origin – transverse process of Superior four or five cervical vertebrae. Insertion – superior vertebral border of scapula Action – Elevates scapula and rotates it downward. Nerve supply – dorsal scapular nerve and cervical spinal nerve

Rhomboid Major Origin – Spine of 2nd to 5th thoracic vertebrae Insertion – vertebral border of scapula inferior to spine of scapula Action – elevates and adducts scapula and rotate it downward; stabilize scapula Nerve – dorsal scapular nerve

Rhomboid Minor Origin – Spine of 7th cervical and 1st thoracic vertebrae. Insertion – Vertebrae border of scapula superior to spine Action – elevates and adducts scapula and rotate it downward; stabilize scapula Nerve – dorsal scapular nerve

Clavicle origin of Pectoralis Major Origin – medial half of anterior clavicle Insertion – greater tubercle and intertubercular sulcus of humerus Action – Flexion, adduction and medial rotation arm at shoulder joint. Nerve supply Medial and lateral pectoral nerve

Sternal origin of Pectoralis Major Origin – anterior surface of sternum, costal cartilage of 2nd -6th ribs. Insertion – greater tubercle and intertubercular sulcus of humerus Action – extend arm at shoulder joint. Nerve supply Medial and lateral pectoral nerve

Latissimus Dorsi Origin – Spines of inferior 6 thoracic vertebrae (T6-T12), lumbar vertebrae (L1-L5), crest of sacrum and illiac crest of hip bone and inferior four ribs. Insertion – Intertubecular sulcus of humerus Action Extends, adduction and medial rotation arm at shoulder joint. Nerve supply - Thoracodorsal nerve

Latissimus Dorsi

Fiber of Deltoid Consists 3 fibers Anterior, middle and posterior fibers. Responsible for movements of the humerus at GH joint Nerve supply – axillary nerve.

Anterior Fiber of Deltoid Origin – anterior border of the lateral one third of the clavicle Insertion – deltoid tuberosity Action – flexion and middle rotation arm at GH joint.

Middle fiber of Deltoid Origin – lateral border and superior surface of the acromion process of the scapula Insertion – deltoid tuberosity Action – abduction arm at GH joint

Posterior Fiber of Deltoid Origin – inferior lip of the crest of the spine of the scapula Insertion – deltoid tuberosity Action – extension and lateral rotation arm at GH joint.

Rotator Cuff Muscles Consists 4 muscles S – Supraspinatus I – Infraspinatus T – teres minor S – Subscapularis Group of muscles that stabilize GH joint.

Supraspinatus Muscle Origin – supraspinous fossa of scapula Insertion – Greater tubercle of humerus (anterior aspect) Action – initially abduction (15 degrees) at shoulder joint, stabilizing shoulder joint Nerve supply - Suprascapular nerve

Infraspinatus Muscle Origin – Infraspinous fossa of scapula Insertion – Greater tubercle of humerus (posterior aspect) Action – Laterally rotation and adduction arm at shoulder joint Nerve supply - Suprascapular nerve

Teres Minor Origin – Inferior lateral border of scapula Insertion – Greater tubercle of humerus (inferior aspect) Action – Laterally rotation, extends and adduction arm at shoulder joint Nerve supply – axillary nerve

Subscapularis Muscle Origin – subscapular fossa of scapula Insertion – lesser tubercle of humerus Action – Medial rotation arm at shoulder joint Nerve supply – upper and lower subscapular nerve

Teres Major Origin – Inferior angle of scapula Insertion – Intertubecular sulcus of humerus Action Extends arm at shoulder joint Assist in adduction and medial rotation of arm at shoulder joint. Nerve supply Lower subscapular nerve

Coracobrachialis Origin - Coracoid process of scapula Insertion - Middle of medial surface of shaft of humerus. Action - Flexion and adduction arm at shoulder joint. Nerve supply - Musculocutaneous nerve

Biceps Brachii Consists 2 head Long head and short head of biceps

Short head of Biceps Origin – Coracoid process of scapula Insertion – radial tuberosity of radius Action – Flexion forearm at elbow joint, flexion arm at GH joint and supination at radioulnar joint. Nerve supply - Musculocutaneous nerve

Long head of Biceps Origin – Tubercle above the glenoid cavity of scapula (supraglenoid tubercle) Insertion – Radial tuberosity of radius Action – flexion forearm at elbow joint, flexion arm at GH joint and supination forearm at radioulnar joint. Nerve supply - Musculocutaneous nerve

Long head of Triceps Origin – tubercle below to glenoid cavity of scapula (infraglenoid tubercle) Insertion – Olecranon of ulna Action - Extends forearm at elbow joint , Extends arm at shoulder joint Nerve supply - Radial nerve Posterior View

Sternomastoid / Cleidomastoid Join together to form sternocleidomastoid muscle Origin (i) Sternomastoid - upper part of the anterior surface of the manubrium of sternum. (ii) Cleidomastoid - superior border and anterior surface of the medial third of the clavicle.

Sternomastoid / Cleidomastoid Insertion – Mastoid process of the mastoid portion of temporal bone. Action - Acting together, flexes the neck, raises the sternum and assists in forced inspiration. Nerve supply – accessory nerve (cranial nerve XI)

Force Couples at Scapulothoracic Joint Serratus anterior produces antero-lateral movement of the inferior angle Upper trapezius pulls scapula medially Forces Couples for abduction 0-90° Deltoid and supraspinatus 90-150 ° Trapezius (Upper and Lower), Serratus anterior, deltoid 150-180 ° As above plus contralateral spinal muscles

Force Couple for Flexion 0-60° Anterior deltoid, coracobrachialis, pectoralis major 60-120° Trapezius (upper & lower), serratus anterior 120-180° Lower trapezius, serratus anterior, contralateral spinal muscles

Scapular Rotation Phase 1 Upper & lower portions of trapezius & serratus anterior produce an upward rotatory force on the scapula Motion at the A-C joint prevented by the oracoclavicular ligament Rotation of the scapula occurs as elevation of the clavicle occurs at the S-C joint

Phase 1

Scapular Rotation Phase 2 Further motion at the S-C joint is prevented by the costoclavicular ligament Continued upward rotation of the scapula pulls on the costo-clavicular ligament causing posterior rotation of the clavicle Posterior rotation of the clavicle allows further rotation of the scapula

Phase 2

Scapular Rotation Necessary to: Enhance glenohumeral stability Elevate acromion to avoid impingement Maintain effective length tension relationship of scapulohumeral muscles