ANATOMY OF SHOULDER REGION

DR. MOHAMMED MAHMOUD MOSAED

The pectoral girdle or shoulder girdle

The pectoral girdle or shoulder girdle is the set of bones which connects the upper limb to the axial skeleton on each side.

It consists of the clavicle and scapula

The only true anatomical joint between the shoulder girdle and axial skeleton is the sternoclavicular joints on each side. No anatomical joint between scapula and the rib cage but there is muscular connection between the two. This permits great mobility of the shoulder girdle

MUSCLES OF THE SHOULDER GIRDLE

• Deltoid. • Supraspinatus.• Infraspinatus • Teres Minor.• Teres Major. • Subscapularis.

Deltoid muscleOrigin:Anterior fibers: from the anterior border of the lateral third the clavicle.

Middle fibers: from the lateral border of the acromion process of the scapula.

Posterior fibers: from the lower border of the spine of the scapula.

Insertion: Into the deltoid tuberosity, on the middle of the lateral surface

of the shaft of the humerus.

Nerve Supply: From the axillary nerve (C5,6).

Action: Anterior fibers: flexes and medially rotates the arm.

Posterior fibers: extends and laterally rotates the arm.

Middle fibers: abducts the arm till the level of the head (from 15° to 90°).

SUPRASPINATUS AND INFRASPINATUSSupraspinatus 

Origin: From the supraspinous fossa of the scapula.Insertion: Into the upper facet (impression) of the greater tuberosity of the humerus and upper part of the capsule of the shoulder joint.Nerve Supply: From the suprascapular nerve (C5,6).Action: Starts abduction of the arm (from 0° to 15°). Stabilizes and supports the shoulder joint (rotator cuff muscle).InfraspinatusOrigin: From the infraspinous fossa of the scapula.Insertion: Into the middle impression of the greater tuberosity of the humerus and posterior part of the capsule of the shoulder joint.Nerve Supply: From the suprascapular nerve (C5,6).Action: Laterally rotates the arm. Stabilizes and supports the shoulder joint (rotator cuff muscle). 

TERES MAJOR AND TERES MINORTeres major

 

Origin: The lower third of the dorsal surface of the lateral border of the scapula.Insertion: The medial lip of the bicipital groove of the humerus.

Nerve Supply: Lower subscapular nerve.

Action: It adducts, extends and medial rotates the arm.

Teres minorOrigin: From the upper 2/3rd of the dorsal surface of the lateral border of the scapula.Insertion: Into the lower facet (impression) of the greater tuberosity of the humerus and posterior part of the capsule of the shoulder joint.Nerve Supply: From the axillary nerve (C 5, 6).

Action: Laterally rotates the arm. Stabilizes and supports the shoulder joint (rotator cuff muscle).

  

SUBSCAPULARIS

Origin: from the subscapular fossa.

Insertion: The lesser tuberosity of the humerus.

Nerve supply: upper and lower subscapular nerves.

Action: It adducts and medial rotates the arm. It stabilizes the shoulder joints.

ROTATOR CUFF• The rotator cuff is the name given to the tendons of

the subscapularis, supraspinatus, infraspinatus, and teres minor muscles, which are fused to the underlying capsule of the shoulder joint.

• The cuff plays a very important role in stabilizing the shoulder joint.

• The tone of these muscles assists in holding the head of the humerus in the glenoid cavity of the scapula during movements at the shoulder joint.

• The cuff lies on the anterior, superior, and posterior aspects of the joint. The cuff is deficient inferiorly, and this is a site of potential weakness.

INTERMUSCULAR SPACES IN THE SHOULDER REGION

A. Quadrangular space Boundaries: above by subscapularis (anterior) and teres minor (posterior). below by teres major. medially by the long head of triceps laterally by the surgical neck of the humerus. Contents: Axillary nerve and posterior circumflex humeral vessels

B. Upper triangular space Is bounded superiorly by the teres minor muscle, inferiorly by the teres major muscle, and laterally by the long head of the triceps.Contents: The circumflex scapular vessels.

C. Lower triangular space Is formed superiorly by the teres major muscle, medially by the long head of the triceps, and laterally by the medial head of the triceps.Contents: The radial nerve and the profunda brachii artery

SUPRASCAPULAR NERVE• The suprascapular nerve arises from the

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

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

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

AXILLARY NERVE• The axillary nerve arises from the posterior cord of the brachial plexus

(C5 and 6) in the axilla. • It passes backward and enters the quadrangular space with the

posterior circumflex humeral artery. • It comes into close relationship with the inferior aspect of the capsule

of the shoulder joint and with the medial side of the surgical neck of the humerus.

• It terminates by dividing into anterior and posterior branches. Branches• An articular branch to the shoulder joint• An anterior terminal branch, which winds around the surgical neck of

the humerus beneath the deltoid muscle; it supplies the deltoid and the skin that covers its lower part.

• 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

ARTERIAL ANASTOMOSIS AROUND THE SHOULDER JOINT

It is an important arterial anastomosis between the branches of the 1st part of the subclavian artery and 3rd part of the axillary artery, ensuring that an adequate blood flow takes place into the upper limb

Anastomosis aroun the scapulaBranches from the Subclavian ArteryThe suprascapular artery, which is distributed to the supraspinous and infraspinous fossae of the scapulaThe superficial cervical artery, which gives off a deep branch that runs down the medial border of the scapulaBranches from the Axillary ArteryThe subscapular artery and its circumflex scapular branch supply the subscapular and infraspinous fossae of the scapula, respectively.

Anastomosis aroud the surgical neck of the humerusThe anterior circumflex humeral arteryThe posterior circumflex humeral artery