Fascia, vessels and nerves of the upper limb

Transcript

The upper limb contains an intricate metro system of blood vessels, muscles, and nerves.

These structures are wrapped up and organized into different compartments by superficial and deep fascia layers, and together they form the multifunctional upper limbs we know and love.

So let’s start with the fascia. You can think of fascia as a pair of thin stockings made of connective tissue that support and bind together different parts of the body, including the lower limbs.

Now, each upper limb actually has two pairs of stockings on top of each other: the superficial fascia, which sits right underneath our skin, and the deep fascia, which is deep to or beneath the superficial fascia, and it sits on top of muscles, organizing them into compartments.

In the upper limb, there are six fasciae to remember. We have the pectoral fascia, the clavipectoral fascia, the axillary fascia, the deltoid fascia, the brachial fascia, and antebrachial fascia.

The wrist and the hand also have fibrous band-like structures called the flexor retinaculum, the extensor retinaculum, and the palmar aponeurosis.

OK, let’s start with the pectoral fascia, which is a broad thin sheath of connective tissue surrounding the pectoralis major muscle, from which it gets its name. Medially, the pectoral fascia is attached to the sternum along with the pectoralis major’s origin.

Superiorly, it attaches to the clavicle, and superolaterally, this fascia passes over this narrow trench called the deltopectoral groove to blend with the deltoid fascia covering the deltoid muscle around the shoulder.

The deltopectoral groove serves as a passageway for the cephalic vein when it is traversing from the arm to enter the lateral aspect of the chest.

Inferiorly, the pectoral fascia spreads downwards and becomes continuous with the fascia of the anterior abdominal wall, while on the lateral side, the fascia curves around the lateral border of the pectoralis major to become continuous with the axillary fascia in the floor of the axilla.

Next comes the clavipectoral fascia, which is deep to the pectoral fascia and pectoralis major. Superiorly, it is attached to the clavicle.

Immediately below the clavicle, the clavipectoral fascia encloses the subclavius muscle and then the pectoralis minor muscle before becoming continuous with the axillary fascia inferiorly.

Between the pectoralis minor and the subclavius, there’s the costocoracoid membrane, which is pierced by the lateral pectoral nerve innervating the pectoralis major, the cephalic vein, and the thoracoacromial artery.

Inferior to the pectoralis minor, the fascia forms the suspensory ligament of the axilla, which supports the axillary fascia and pulls the skin up when abducting the arm creating the axillary fossa, or armpit.

Unsurprisingly, the fascia covering the deltoid muscle is called the deltoid fascia. Superiorly, the deltoid fascia attaches to the clavicle, the acromion process and the spine of the scapula.

It then spreads downwards to cover the superficial surface of the deltoid muscle. Inferiorly, it merges with the pectoral fascia on the anteromedial side, the infraspinous fascia posteriorly, and the fascia of the arm distally.

Alright, now let’s have a look at the fascia of the arm, also called the brachial fascia. The brachial fascia is a tough connective tissue looking like the sleeve of a t-shirt covering the muscles of the arm.

Proximally, the brachial fascia is continuous with the deltoid, the axillary, and the pectoral fasciae, while distally the brachial fascia attaches to the epicondyles of the humerus and the olecranon of the ulna, and blends with the antebrachial fascia of the forearm.

The brachial fascia sends medial and lateral intermuscular septa inwards to the shaft and medial and lateral supracondylar ridges of the humerus, which divide the arm into two compartments; the anterior and posterior compartments.

The anterior compartment is also called the flexor compartments because it houses muscles responsible for the elbow flexion, while the posterior compartment is called the extensor compartment because it houses muscles responsible for elbow extension.

At its distal part, the brachial fascia is continuous with the antebrachial fascia or just the fascia of the forearm.

The antebrachial fascia surrounds the muscles of the forearm, which are divided into two compartments by an intermuscular septum and a band of fibrous connective tissue called the interosseous membrane.

It is called the interosseous membrane because it connects two bones together, the radius and the ulna.

The two compartments of the forearm are the posterior compartment, also called the extensor-supinator compartment as it contains muscles that extend the wrist and supinate the forearm, and the anterior or flexor-pronator compartment, which contains muscles that flex the wrist and pronate the forearm.

Over the posterior side of the arm, the fascia becomes thicker as it reaches the distal radius and ulna, eventually transforming into a transverse band known as the extensor retinaculum, which holds the extensor tendons in position.

On the anterior side, the antebrachial fascia also forms another thick fibrous band continuous with the extensor retinaculum referred to as the palmar carpal ligament.

Distal and deeper to the palmar carpal ligament lies the flexor retinaculum, which is another fibrous band that extends between the anterior prominences of the outer carpal bones.

Medially, the flexor retinaculum attaches to the pisiform and the hook of the hamate, while on the lateral side it attaches to the tubercle of scaphoid and the crest of the trapezium.

Together, the flexor retinaculum and the anterior concave surface made by carpal bones, form an osseofibrous tunnel called the carpal tunnel, which serves as a passageway for a nerve called the median nerve and the flexor tendons of the forearm.

In the hand, the antebrachial fascia extends beyond the flexor and extensor retinacula and becomes the palmar fascia.

As it enters the hand, the central part of the palmar fascia, called the palmar aponeurosis, is a thick, tendinous, and triangular structure that covers the central compartment of the palm.

Proximally, the apex of this palmar aponeurosis blends with the flexor retinaculum and the tendon of the palmaris longus muscle.

Moving distally, four longitudinal bands radiate distally from the apex of the palmar aponeurosis. At the bases of the fingers, they become continuous with the fibrous tendon sheaths of the digits.

The medial border of the palmar aponeurosis becomes continuous with the hypothenar fascia, the one that covers the hypothenar muscles.

On its lateral border, the palmar aponeurosis becomes continuous with the thenar fascia covering the thenar muscles.

Alright!! Now let’s pause for a minute and see if you can identify the six fasciae of the upper limb! And now let’s switch gears a little bit, and talk about the veins of the upper limb, which can also be superficial or deep veins.

The superficial veins are those which can be found in the superficial fascia and are easily accessible, for example when you need to have a blood sample taken.

Initially, the superficial veins of the upper limb start as small veins in the subcutaneous tissues from the dorsal venous network of the hand.

They converge into bigger venous networks as they progress proximally up along the wrists and the forearm, resulting in big superficial veins called the cephalic vein, the basilic vein, and the median antebrachial vein also known as the median vein of the forearm.

The cephalic vein arises in the converging network of small veins from the lateral aspect of the dorsal venous network.

The cephalic vein then ascends on the lateral border of the wrist, and travels up the anterolateral surface of the forearm and arm and is often visible through the skin.

Anterior to the elbow, the cephalic vein communicates with the median cubital vein which passes obliquely across the cubital fossa to meet up with the basilic vein which drains the medial side of the upper limb.

The cephalic vein continues its course superiorly in the arm on the lateral side between the deltoid and pectoralis major muscles in the deltopectoral groove and then through the deltopectoral triangle, a triangular space bordered by the clavicle, the lateral border of pectoralis major muscle, and the medial border of the deltoid muscle.

At this level, the cephalic vein empties into the terminal part of the axillary vein after it pierces the costocoracoid membrane of the clavipectoral fascia.

Similar to the cephalic vein, the basilic vein ascends in the subcutaneous tissue from the medial end of the dorsal venous network along the medial side of the forearm and inferior part of the arm.

Then, it pierces the brachial fascia to pass deep near the junction of the middle and inferior thirds of the arm, running superiorly, parallel to the brachial artery, eventually merging with the deep veins accompanying the brachial artery to form the axillary vein.

The median antebrachial vein is highly variable, and it usually starts at the base of the dorsum of the thumb, and then ascends between the cephalic and the basilic veins territories at the anterior aspect of the forearm.

It then joins the basilic vein below the cubital fossa, but in a few individuals, it can divide into a median cephalic vein draining into the cephalic vein and a median basilic vein that drains in the basilic vein. Makes sense, right?

OK, now let’s have a look at the deep veins. Unlike the superficial veins, the deep veins are located deep to the muscles, and they commonly accompany major arteries, so they’re called the “venae comitantes”, which is Latin for accompanying veins.

Just like the superficial veins, the deep veins start as a tiny network but this time it’s deep in the hand. These tiny veins then form the superficial and deep palmar venous arches.

On the medial side, this network gives rise to the ulnar veins which ascends alongside the ulnar artery on the medial side of the forearm.

On the lateral side of the hand, the deep palmar venous arch gives rise to the radial veins, which climbs up the forearm alongside the radial artery.

Both the ulnar and the radial veins terminate in the cubital fossa where they join to form the big deep veins of the arm known as the brachial veins.

Travelling alongside the brachial artery, the brachial veins continue up the arm, where they join the basilic vein to form the axillary vein.

Alright, so before we continue, let’s have you take a small pause and try to identify the three big superficial veins and two deep veins of the upper limb.

Now, alongside the veins run the lymphatic vessels which are responsible for the lymphatic drainage of the upper limb.

Their major function is to collect excess fluids in the extracellular space, and bring it back into the venous circulation.

Just like the veins, lymphatic vessels are also divided into superficial and deep lymphatic vessels.

The superficial lymphatic vessels of the upper limb also start as a network of tiny lymph vessels in the skin of the hand called the lymphatic plexuses, and they converge into bigger lymph vessels that ascend the upper limb mostly alongside the cephalic and basilic veins.

Some of the lymphatic vessels which travel alongside the basilic vein drain in the cubital lymph nodes. These lymph nodes are located medial to the basilic vein and proximal to the medial epicondyle of the humerus.