3 - Upper limb 1 (Exam 2)

• The upper limb is suspended from the shoulder and extends from the shoulder joint to the wrist.
• The arm (brachium) is the region between the shoulder joint and the elbow.
• The forearm (antebrachium) is located below the elbow and joins the hand at the wrist.

Blood Supply

• Blood supply ascends from the thoracic cavity off the aortic arch.
• The subclavian artery distributes blood to the upper limb.
• The subclavian artery passes over the first rib and into the axilla.
• The subclavian artery becomes the axillary artery in the axilla.
• The axillary artery becomes the brachial artery on leaving the axilla and entering the arm.
• The brachial artery terminates just below the elbow by bifurcating into the ulnar and radial arteries.
• The ulnar and radial arteries pass through the anterior forearm.
• The ulnar and radial arteries unite again in the hand via superficial and deep palmar arches.
• Arterial vessels lie in the anterior part of the limb.
• Posterior aspects being supplied by branches.
• The subclavian and axillary arteries supply the scapular region with blood.
• The profunda brachii supplies the back of the arm.
• The posterior interosseous artery (branch off ulnar artery) supplies the posterior forearm.

Venous Drainage

• Deep structures are drained by veins, often paired that extend alongside the arteries (venae comitantes).
• The venae comitantes eventually form or open into the axillary vein, which then becomes the subclavian vein when it enters the thorax.
• Superficial structures are drained by subcutaneous veins that also empty into the axillary vein.
• Includes dorsal and palmar digital veins that drain to the dorsal venous network on the dorsum of the hand.
• Two veins ascend into the forearm from the medial and lateral aspects of the dorsal venous network:
  • The basilic vein ascends medially to the middle of the arm, pierces the fascia, and contributes to the formation of the axillary vein.
  • The cephalic vein passes laterally onto the anterior aspect of the forearm.
• In the cubital fossa, the cephalic vein communicates with the basilic vein via the median cubital vein (short, visible, and immobile).
• The cephalic vein continues up the lateral side of the arm and joins the axillary vein in the deltopectoral groove.

The Median Cubital Vein

• A median vein of the forearm is also often prominent and joins the median cubital vein superiorly.
• The superficial veins lie superficial to the deep investing fascia of the upper limb.
• In the cubital fossa, cephalic vein is lateral and the basilic vein is medial, both superficial to the deep investing fascia.
• The median cubital vein passes obliquely through the fossa and accepts the median antebrachial vein, superficial to the bicipital aponeurosis.
• The bicipital aponeurosis is an aponeurotic layer of fascia arising from the tendon of the biceps brachii which passes medially across the fossa and fuses with the deep fascia of the forearm.
• The brachial artery lies deep to this fascia, effectively separating it from the overlying median cubital vein.

Innervation

• Nerve supply descends from the cervical region to join the blood supply in the axilla.
• The supraclavicular nerves (C3,4) from the cervical plexus (C1-4) supply the skin over the shoulder.
• The anterior rami of C5-8 and T1 form the brachial plexus.
• The median, musculocutaneous, and ulnar nerves supply the skin and muscles of the anterior (flexor) part of the limb.
• The axillary, radial, and posterior interosseous nerves supply the skin and muscles of the posterior (extensor) part of the limb.

Muscles That Connect the Upper Limb to the Trunk

• Muscles Arising From the Vertebral Column:
  • Posteriorly, these muscles arise from the occipital bone, cervical, thoracic, lumbar, and sacral spines, and the iliac crest.
  • The included muscles are:
    • The trapezius rotates the scapulae when the limb is raised above the head.
    • The trapezius stabilizes the shoulder in upper limb movements (accessory n.).
    • The levator scapulae rotates the scapula with the rhomboids in the opposite direction to the trapezius.
    • The rhomboideus major and minor stabilize and brace the shoulder, and rotate the inferior angle of the scapula.
  • The latissimus dorsi is an adductor of the upper limb.
• Muscles Arising From the Thoracic Wall
  • Pectoralis major adducts the arm with the latissimus dorsi and assists with medial rotation.
  • Pectoralis minor pulls the scapulae forward and can raise ribs in respiratory distress when the shoulder girdle is fixed.
  • Serratus anterior draws the scapulae forward and rotates the inferior angle of the scapula laterally, turning the glenoid cavity upwards when the arm is raised above the head.

Muscles of the Scapular Region

• A group of short, stout muscles located between the scapula and upper humerus are essential to the stability and movement of the shoulder joint.
• The first four muscles form the rotator cuff:
  • The subscapularis stabilizes the head of the humerus in the shallow glenoid cavity. With the arm by the side, its attachment facilitates medial rotation of the humerus at the shoulder.
  • The supraspinatus stabilizes and prevents the head of the humerus from slipping down off the glenoid cavity and abducts the arm with the deltoid.
  • The infraspinatus rotates the arm laterally and stabilizes the shoulder joint.
  • The teres minor stabilizes and produces lateral rotation of the arm.
• The tendons of the rotator cuff muscles surround the shoulder joint on all sides except inferiorly (a common dislocation site).
• They keep the large head of the humerus applied to the shallow glenoid cavity.
• The teres major adducts and medially rotates the arm.
• It can be thought of as a portion of the subscapularis that has migrated onto the dorsum of the scapula and has a similar nerve supply (lower scapular n.).
• The deltoid forms the "cap" of the shoulder and provides a wide range of actions at the shoulder.
  • Anterior fibers flex the arm.
  • Posterior fibers extend the arm back behind the body.
  • Intermediate fibers are powerful abductors of the arm.

The Quadrangular and Triangular Spaces

• Muscle configurations below the shoulder allow structures to pass from anterior to posterior regions of the axilla and arm.
• Quadrangular space: Transmits the axillary nerve and posterior circumflex artery.
• Triceps hiatus (medial to the shaft of the humerus): Transmits the radial nerve and profunda brachii artery.
• Triangular space (inferior to the quadrangular space): Passes the circumflex scapular branch of the subscapular artery.

Axillary Artery

• The axillary artery is a continuation of the subclavian artery.
• It begins at the lateral edge of the first rib (R1) and becomes the brachial artery as it passes the lower border of the teres major.
• The axillary artery is divided into 3 parts by the overlying pectoralis minor muscle.
• The number of divisions is equivalent to the number of branches from that division:
• Branches from the first part:
  • Superior thoracic artery: supplies the pectoralis major & minor.
• Branches from the second part:
  • Thoracoacromial artery: A short trunk supplying the pectoral, acromial, clavicular, and deltoid regions.
  • Lateral thoracic artery: contributes substantially to the breast.
• Branches from the third part:
  • Subscapular artery is the largest branch of the axillary artery.
  • This gives rise to muscular branches that form an anastomosis around the scapula.
  • The anterior and posterior circumflex humeral arteries form an anastomotic circle around the surgical neck of the humerus.
  • The anterior is small, and the posterior extends through the quadrangular space with the axillary nerve to supply the shoulder joint and surrounding muscles.