DELTOID MUSCLE

Deltoid muscle

Deltoid:

• Large superficial muscle of shoulder

• Gibes contour shape

Origin:

anteriorly: it originates from the superior aspects of the lateral 1/3rd of the clavicle(while medial 2/3 giving attachment to pectoralis major muscle)

Laterally : originates from the lateral margin and superior part of the acromion process  of the scapula -4 inter muscular septa

Posteriorly : from the inferior edge of the spine of the scapula(comes from the lower lip of the spinus process of scapula

DIVIDED INTO 3 SETA OF FIBER’S

• Anterior : clavicular fibers (unnipennate)

• Lateral : acromial fibers ( multipennate)

• Posterior: spinal fibers (unnipennate)

The fiberss of the deltoid muscle converts to form a short tendon which insects on to the "deltoid tuberosity" on the lateral aspects of humerous.

• Anterior fibers : flexor 

• Posterior fibers : extension ,external rotation

• Lateral fibers :  acromial fibers are the powerful abducters of the arm(assisted by the superspinatus of the rorator cuff in this movement

The deltoid muscles receives its anterior supply by the acromial and  deltoid branches of the thoracco- acromial artery 

At the anterior and posterior circumflex humeral artery 

It also receives supply from a sub scapular artery and the deltoid branch of profunda brachii .

It is innovated by the axillary nerve which Aries from  the posterior end of the brachial plexus.

Nerve supply of deltoid : axillary nerve ,root value (c5 , c6)

Sensory loss over the lower half of deltoid called regimental badge anaesthesia:occurs because of the injury in axillary nerve 

• Axillary nerve supply muscles and also skin.

Actions:

1. Anterior /clavicular fibres

    Flexion adduction and medial rotation of       arm

2. middle / acromial fibers : ( antigravity muscle )

   Eg: shunt muscle 

     Abduction of arm from 15° to 90°

3. Posterior fibres extension and lateral rotation of arm

Special features of deltoid :

⁃ Acromial part (middle part) of deltoid is multipennate and strongest 

⁃ It arise from lateral border of acromian and  from four septa 

⁃ These four intramuscular Sapta descended from the acromion to interdigitate  with 3 septa ascending  from the Deltoid tubercle

Structures undercover of the deltoid:

Bones

1. Coracoid process

2. Lesser and greater tubercle of humerus

3. Enter tubercular sulcus

4. Upper part of shaft

5. Surgical neck of humerus

Muscle

1. Pectoralis minor

2. Coracobrachialis 

3. Origin of biceps brachii

4. Pectoralis major

5. Teres major

6. Latissimus dorsi 

7. Subscapularis

8. Supra spinatous

9. Infra spinatous

10. Teres minor

11. Long head of triceps

Vessels and nerve :

• Anterior and posterior  circumflex scapular vessels 

• Axillary nerve