4 - Upper limb 2

• The arm refers to the segment of the upper limb from shoulder to elbow.
• There are two compartments surrounding the humerus: flexor (anterior) and extensor (posterior).
• The brachial fascia surrounds the arm, giving off lateral and medial intermuscular septa which effectively create these compartments.

Flexor Compartment Contents

• Biceps brachii
• Coracobrachialis
• Brachialis
• Brachial artery and vein
• Musculocutaneous nerve (motor to flexors)
• Median nerve
• Proximal ulnar nerve

Biceps Brachii

• The biceps brachii has two heads
• The long head originates from the supraglenoid tubercle in the capsule of the shoulder joint
• The short head originates from the tip of the coracoid process
• The two bellies fuse in the lower anterior compartment
• The distal flattened tendon crosses the elbow joint
• Attaches to the posterior aspect of the radial tuberosity
• The bicipital aponeurosis is given off as the tendon crosses the elbow joint
• It passes medially across the brachial artery
• It fuses with the deep fascia of the forearm and the periosteum over the ulna
• This providing secondary attachment

Biceps Brachii Nerve Supply

• Both heads are supplied by the musculocutaneous nerve after piercing the coracobrachialis
• The biceps is a shoulder flexor
• A strong flexor at the elbow
• A powerful supinator of the forearm

Extensor Compartment Contents

• Triceps brachii
• Terminal branch of profunda brachii
• Radial nerve (motor to extensors)
• Distal ulnar nerve (crosses to posterior)
• The median and ulnar nerves have no branches in the arm

Triceps Brachii

• It extends the arm
• Triceps brachii is the only muscle in the posterior compartment of the arm
• It has three heads
• All three bellies fuse into a common tendon
• The tendon inserts into the olecranon process of the ulna
• All three heads are innervated by branches of the radial nerve
• It is the only effective extensor of the elbow joint

Cubital Fossa

• It is an inverted triangular region anterior to the elbow joint
• The base is an imaginary line through the medial and lateral epicondyle of the humerus
• The lateral boundary is the brachioradialis
• The medial boundary is the pronator teres
• The roof is formed by the skin, superficial fascia, and the bicipital aponeurosis of the biceps brachii
• The median cubital vein lies superficial to the aponeurosis
• The brachial artery lies deep to it
• Starting from the lateral (radial) aspect - removal of the roof reveals the: tendon of the biceps, the brachial artery, the median nerve

Forearm

• The forearm, similarly to the arm, has an anterior (flexor) and posterior (extensor) compartment
• The forearm must be supinated to be in anatomical position

Flexor Compartment

• The flexor compartment muscles are further divided into superficial and deep groups
• The superficial group of flexors are innervated by the median nerve except for the flexor carpi ulnaris, innervated by the ulnar nerve
• The deep group of forearm flexors lies undercover of the superficial group, mainly innervated by the median nerve
• The four tendons of the flexor digitorum profundus pass into the hand under the flexor retinaculum

Flexor Digitorum Profundus Innervation

• The innervation of the flexor digitorum profundus muscle is unusual
• Its medial part/tendons are innervated by the ulnar nerve
• The lateral part/tendons are innervated by the median nerve
• The brachial artery enters the forearm through the cubital fossa, dividing into the radial and ulnar arteries

Forearm Nerves

• The median and ulnar nerves traverse the flexor compartment supplying all the muscles within
• The ulnar nerve is joined by the ulnar artery on the medial aspect of the compartment
• The radial nerve enters the forearm and immediately divides into superficial and deep branches
• Only the deep branch enters the extensor compartment
• The superficial branch is cutaneous to the dorsum of the hand, with no muscular or cutaneous branches

Extensor Compartment

• The muscles in the posterior (extensor) compartment again are divided into superficial and deep groups
• The superficial group innervated by the radial nerve extends the wrist and digits
• The deep group lies beneath the superficial group
• All muscles form long tendons that cross the wrist and enter the hand, except the supinator

Forearm Arteries

• No major artery reaches the extensor compartment of the forearm from the arm
• The ulnar artery forms the anterior (flexor) compartment
• A short trunk is given off that divides into anterior and posterior interosseous arteries
• Both vessels supply structures in the extensor compartment
• The two interossei anastomose at the upper pronator quadratus border
• Continues into the wrist where it joins the dorsal carpal arch

Forearm Nerves

• The brachioradialis and the extensor carpi radialis longus are supplied by the radial nerve
• The nerve divides at the elbow into superficial and deep branches

Dorsum of Hand

• Except for the dorsal interosseous muscles, there are no intrinsic muscles to the dorsum
• Tendons encountered arise from muscles with bellies in the extensor compartment of the forearm
• Tendons crossing the wrist joint are surrounded by synovial sheaths and the extensor retinaculum

Dorsum Nerves

• There are no intrinsic muscles innervated on the dorsum so radial and ulnar nerve supply cutaneous innervation

Palm

• The fatty superficial fascia is divided into loculi by fibrous septa that anchors the skin to the deep fascia
• In the central region, the deep fascia is continuous with a sheet of fibrous tissue, known as the palmar aponeurosis
• This covers the palm between the thenar and hypothenar eminences

Flexor Retinaculum of the Wrist

• The flexor retinaculum keeps the long flexor tendons close to the wrist and palm during flexion
• The retinaculum spans the concave palmar aspect of the carpus and forms the osseofibrous carpal tunnel
• The median nerve and long flexor tendons pass through the tunnel
• A septum descends to the underling trapezium, to form a tunnel for the flexor carpi radialis tendon

Thenar Eminence

• The raised region between the wrist and the base of the thumb consists of the: abductor pollicis brevis, flexor pollicis brevis, and the opponens pollicis
• All three muscles are supplied by the median nerve

Hypothenar Eminence

• A region between the wrist and base of the little finger
• Less prominent than the thenar eminence
• Composed of the abductor digiti minimi, flexor digiti minimi, and opponens digiti minimi
• All three muscles are innervated by the ulnar nerve

Median Nerve in Hand

• Appears from under the flexor retinaculum and gives off a muscular branch to the thenar eminence
• Within the carpal tunnel it was superficial to the long flexor tendons
• Pressure or irritation, "carpal tunnel syndrome" may occur
• This can cause sensory changes and wasting of the thenar muscles

Ulnar Nerve in Hand

• The ulnar artery and nerve pass lateral to the flexor retinaculum
• The nerve divides into a deep and superficial branch

Ulnar Nerve Branches

• The superficial branch innervates the palmaris brevis and supplies palmar digital nerves to the remaining half of the 4th finger and both sides of the 5th finger
• The deep branch is another motor nerve supplying the muscles of the hypothenar eminence
• It also supplies the medial lumbricals and all the interossei
• Both heads of the adductor pollicis are also innervated

Radial Artery

• Passes from the lateral anterior compartment to the dorsum of the hand
• Passes through the anatomical snuff box
• Passes back onto the palm of the hand by passing between the two heads of the adductor pollicis
• It anastomoses with the deep palmar branch of the ulnar artery

Ulnar Artery

• Forms the deep palmar arch lying deep to the long flexor tendons
• The radial artery is a major contributor is stated to the deep palmar arch
• The radial also gives off a superficial palmar branch which anastomoses with the ulnar artery
• Helps form or complete the superficial palmar arch lying just beneath the palmar aponeurosis
• The ulnar artery is stated as the major contributor to the superficial palmar arch

Test your knowledge on the flexor compartment of the arm! This quiz covers the muscles, nerves, and anatomical structures. Questions pertain to function, innervation, and attachments of key components.