Muscle of the back• Muscle are arranged in 2 layers:1. Superficial layer: trapezius and latissimus dorsi2. Deep layer: levator scapulae, rhomboidus minor and

major1. Trapezius

Origin: 1. The upper fibers arises from medial third of superior

nuchal line & external occipital protuberance 2. The middle fibers arises from nuchal ligament & spinous

process of C7 3. The lower fibers arises from spinous processes of all

thoracic vertebrae and supraspinous ligamentInsertion: 1. The upper fibers pass downwards and forwards to be

inserted to the posterior border of the lateral third of the clavicle

2. The middle fibers pass transversly to the medial border of acromion and upper lip of the crest of spine of scapula

3. The lower fibers are inserted into rough tubercle on the crest of the spine of scapula

Nerve supply: spinal part of accessory nerve

Actions:

• Upper fibers elevates the scapula

• middle fibers retracts scapula;

• Lower fibers together with the lower five digitations of serratus anterior rotate the scapula laterally as in raising the arm above the head

Latissimus dorsi • Origin: 1.Tips of spinous processes of the lower 6 thoracic

vertebrae and supraspinous ligament2. thoracolumbar fascia, 3.Outer lip of iliac crest, 4. lower 3 or 4 ribs • Insertion: Floor of intertubercular groove of

humerus • Nerve supply: Thoracodorsal nerve (C6, C7, C8) • Action: Extends, adducts, and medially rotates the

arm as in swimming and raises body toward arms during climbing

Levator scapulae

• Origin: from posterior tubercles of transverse processes of C1 to C4 vertebrae

• Insertion: into the posterior aspect of the medial border of scapula from the superior angle to the root of spine

• Nerve supply: from dorsal scapular nerve (C5)

• Action: Elevates scapula and rotates it medially so the glenoid cavity looks downwards

Rhomboidus minorOrigin: ligamentum nuchae and spinous processes of C7 and T1Insertion: posterior aspect of the medial margin of the scapula

opposite its spineNerve supply: Dorsal scapular nerve (C4, C5) Action: Retract scapula and rotates it medially to depress the

glenoid cavity

Rhomboidus majorOrigin: spinous processes of T2 to T4 vertebrae and

supraspinous ligament

Insertion: posterior aspect of the medial border of scapula from level of spine to inferior angle

Nerve supply: Dorsal scapular nerve (C4, C5)

Action: the same as rhomboidus minor

Shoulder region1. Deltoid muscle

Origin: •Anterior borders of lateral third of clavicle; •Lateral border of acromion•Lower lip of the crest of the spine of scapula Insertion: Deltoid tuberosity of humerus Nerve supply: Axillary nerve (C5, C6) Action: 1. Anterior fibers: flexes and medially rotates the arm

2. Middle fibers: abducts the arm from 15 to 90 degrees

3. Posterior fibers: extends and laterally rotates the arm

• Subacromial bursa: it is a large bursal sac that lies between the acromion and deltoid muscle superiorly and muscles on the upper surface of the capsule of shoulder joint inferiorly.

• Coracoacromial arch: it is formed by the coracoid process, acromion, and coraco-acromial ligament. It is separated from the shoulder joint by subacromial bursa and tendons of supraspinatus, infraspinatus and subscapularis. It overhangs and protects the shoulder joint

2 .Supraspinatus Origin: from the medial two-thirds of the

supraspinous fossa Insertion: fibres converge into a tendon which

crosses above the shoulder joint and is attached to the highest facet of the greater tuberosity of the humerus.

Nerve supply: suprascapular nerve, C5 and 6. Action: 1. initiates abduction of the arm from 0

to 15 degrees 2. it helps to stabilize the head of the humerus in the

glenoid fossa during shoulder movements as one of the rotator cuff muscles.

3 .Infraspinatus Origin: from the medial two-thirds of the fossa

Insertion: Its fibres converge to a tendon which passes behind the shoulder joint to be attached to the middle facet on greater tuberosity of humerus.

Nerve supply: suprascapular nerve, C5 and 6.

Action:

1. lateral rotator of the arm.

2. it helps to stabilize the head of the humerus in the glenoid fossa during shoulder movements as one of the rotator cuff muscles.

N.B. rotator cuff muscles are: supraspinatus, infraspinatus, subscapularis and teres minor

4 .Teres minorOrigin: from the upper two-thirds of a flattened strip on posterior surface of scapula adjoining its lateral border,

Insertion: to the lowest facet of the greater tuberosity of the humerus.

Nerve supply: Axillary nerve (C5, C6) Action: Laterally rotate the arm

5 .Teres majorOrigin: from the lower third of a strip on the posterior

surface of the scapula adjoining its lateral border

Insertion: to the medial lip of the intertubercular sulcus of the humerus.

Nerve supply: Lower subscapular nerve (C5, C6)

Action: Adducts and medially rotates the arm

6 .Subscapularis • Origin: from medial two thirds of the subscapular fossa

of the scapula• Insertion: into the lesser tubercle of humerus • Nerve supply: Upper and lower subscapular nerves

(C5, C6) • Action: Medially rotates and adduct arm and helps hold

humeral head in glenoid cavity • Subscapular bursa: 1. it is prolongation of the synovial membrane of shoulder

joint through a gap in the upper anterior part of capsule. 2. It extends between subscapularis muscle and the

medial part of the capsule, front of the neck of scapula and root of coracoid process.

3. facilitates movement of subscapularis over these parts.

Intermuscular Spaces I- Quadrangular space:

1. Boundaries: as follows:• Above: the subscapularis and capsule of

the shoulder joint, • Below: the teres major muscle, • Medially: the long head of the triceps and • Laterally: the surgical neck of the

humerus.2. Contents: The axillary nerve and the

posterior circumflex humeral vessels pass backward through this space.

II- The upper triangular space :

1. Boundaries: as follows:

• above by subscapularis anteriorly, teres minor posteriorly,

• below by teres major, and

• laterally by the long head of triceps.

2. Contents: The circumflex scapular artery

III- The lower triangular space :

1. Boundaries:

• above by subscapularis anteriorly and teres major posteriorly

• medially by the long head of triceps

• laterally by the humerus.

2. Contents: The radial nerve and the profunda brachii vessels

The suprascapular nerve:

• Beginning: from the upper trunk of the brachial plexus (C5 and 6) in the posterior triangle in the neck.

• Course: It runs downward and laterally and passes beneath the suprascapular ligament, which bridges the suprascapular notch, to reach the supraspinous fossa.

• Distribution: It supplies the supraspinatus and infraspinatus muscles and the shoulder joint.

Axillary Nerve• Beginning: The axillary nerve arises from the posterior

cord of the brachial plexus (C5 and 6) in the axilla. • Course: It passes backward and enters the

quadrangular space with the posterior circumflex humeral artery. it comes into close relationship with the surgical neck of the humerus. It terminates by dividing into anterior and posterior branches

• Branches1. An articular branch to the shoulder joint2. An anterior terminal branch supplies the deltoid and

the skin that covers its lower part.3. A posterior terminal branch, which gives off a branch

to the teres minor muscle and a few branches to the deltoid, then emerges from the posterior border of the deltoid as the upper lateral cutaneous nerve of the arm

Diagram of circumflex arteries and axillary nerve

1. Axillary artery

2. Anterior circumflex humeral artery

3. Posterior circumflex humeral artery

4. Axillary nerve

5. Articular branch

6. T.S. of humerus

7. Branch to teres minor

8. Cutaneous branches

Anastomosis around the scapula• Three arteries share in the anastomosis:1. Deep branch of transverse cervical artery: arises from

thyrocervical trunk from the first part of subclavian artery. It descends along the medial border of scapula and gives branches to both surfaces of scapula

2. Suprascapular artery: arises from the thyrocervical trunk that originates from the first part of subclavian artery. It passes over suprascapular ligament giving branches to supraspinatus, then it descends through the spinoglenoid notch to end by ramifying in infraspinatus

3. Subscapular artery arises from the 3rd part of axillary artery. It descends along the lower border of subscapularis giving branches as the circumflex scapular artery which anastomosis with the branches of the previous arteries

• This anastomosis is important as if a ligature is applied to the artery between the 1st part of subclavian and 3rd part of axillary, collaterals of anastomosis open and establish sufficient arterial supply for the upper limb.