Cutaneous Innervation, Venous Drainage, and Lymphatic Drainage of Lower Limb

Cutaneous Innervation

• The skin of the lower limb is supplied by several cutaneous (sensory) nerves.
• These nerves arise mainly from the L1 to L5 and S1 to S3 spinal nerve segments.
• A small area of skin also receives sensory supply from the T12 and S4 spinal nerve segments.

Peculiarities of cutaneous nerves of lower limb

1. Almost the entire skin of the lower limb is supplied by the ventral primary rami of the spinal nerves.
2. The superomedial quadrant of the gluteal region is an exception. This area is supplied by the dorsal primary rami of the L1–L3 and S1–S3 spinal nerves.
3. The area supplied by a cutaneous nerve does not always correspond to a single spinal segment because many nerves contain fibers from more than one spinal level.
4. The sensory areas of adjacent cutaneous nerves overlap, so there is no sharp boundary between their areas of supply.

Cutaneous nerve of lower limb

The skin of the lower limb receives sensory innervation from the following nerves:

1. Lateral cutaneous branch of the subcostal nerve
2. Lateral cutaneous nerve of the thigh
3. Femoral branch of the genitofemoral nerve
4. Branches of the femoral nerve:
5. Intermediate cutaneous nerve of the thigh
6. Medial cutaneous nerve of the thigh
7. Saphenous nerve

5. Lateral cutaneous branch of the iliohypogastric nerve
6. Dorsal primary rami of the L1–L3 and S1–S3 spinal nerves
7. Posterior cutaneous nerve of the thigh
8. Obturator nerve
9. Lateral cutaneous nerve of the calf
10. Sural communicating branch of the common peroneal nerve
11. Sural nerve
12. Superficial peroneal (fibular) nerve
13. Deep peroneal (fibular) nerve
14. Branches of the medial and lateral plantar nerves
15. Medial calcaneal nerve

Dermatoes of Lower Limbs

• A dermatome is an area of skin supplied by the sensory fibers of a single spinal nerve.
• During embryonic development, the lower limb grows away from the trunk. As it develops, the dermatomes move with the limb and carry their associated nerves and blood vessels.

Peculiarities of dermatomes of lower limb

1. The skin of the lower limb is supplied by the L1–L5 and S1–S3 spinal nerve segments.
2. Most of the lower limb receives sensory supply from the ventral primary rami of these spinal nerves.
3. The superomedial quadrant of the gluteal region is an exception. It is supplied by the dorsal primary rami of the L1–L3 and S1–S3 spinal nerves.
4. Adjacent dermatomes overlap with each other. Therefore, injury to a single spinal nerve usually causes partial sensory loss rather than complete loss of sensation in its dermatome.
5. During development, the lower limb rotates medially by about 90°. As a result, the original preaxial border of the limb, represented by the great toe and tibia, comes to lie on the medial side of the limb.

Axial lines of lower limb

• An axial line is a line that separates two adjacent dermatomes supplied by non-consecutive spinal nerve segments.
• It forms the boundary between the areas supplied by the L1–L4 spinal segments and the S2 spinal segment.
• The lower limb has two axial lines:
  • Ventral axial line
  • Dorsal axial line

Table 18.1: Segmental innervation of lower limb

Area of Skin	Main Spinal Segment(s)
Front (anterior) of the thigh	L1–L4
Medial side of the leg	L4
Lateral side of the leg and medial side of the foot	L5
Lateral border of the foot and most of the sole	S1
Middle of the back (posterior) of the thigh and leg	S2
Buttock region around the gluteal fold and perineal area	S3–S4
Heel	S1–S2

Table 18.2: Segmental innervation of joints of the lower limb

Joint	Movement	Main Spinal Segment(s)
Hip joint	Flexion	L2–L3
	Extension	L4–L5
	Adduction	L2–L4
	Abduction	L5–S1
	Medial rotation	L4–L5
	Lateral rotation	L5–S1
Knee joint	Extension	L3–L4
	Flexion	L5–S1
Ankle joint	Dorsiflexion	L4–L5
	Plantar flexion	S1–S2
Joints of the foot	Inversion	L4–L5
	Eversion	L5–S1

Veins of Lower Limb

• The veins of the lower limb are commonly affected by various clinical conditions, such as varicose veins and deep vein thrombosis.
• They are also frequently used in surgical procedures, including vein grafts and venous access.

Factors helping venous return in lower limb

Venous blood in the lower limb has to travel upward against gravity. The following factors help return blood to the heart:

1. Peripheral heart (calf muscle pump): Contraction of the calf muscles compresses the deep veins and pushes blood upward toward the heart. Because of this important pumping action, the calf muscles are called the peripheral heart.
2. Arterial pulsations: The pulsation of nearby arteries compresses the adjacent veins and helps move venous blood upward.
3. Venous valves: Veins contain valves that ensure one-way blood flow toward the heart. These valves also direct blood from the superficial veins to the deep veins and prevent the backward flow (reflux) of blood.
4. Negative intrathoracic pressure: During inspiration, the pressure inside the thoracic cavity becomes more negative. This creates a suction effect that helps draw venous blood from the lower limbs toward the heart.
5. Vis-a-tergo: This refers to the forward pressure generated by the pumping action of the ventricles. It helps move blood through the veins, especially when a person is lying down.
6. Muscular walls of the veins: The veins of the lower limb have thicker muscular walls than veins in many other parts of the body. This helps support efficient venous return.
7. Deep fascia: The deep fascia forms a tight sleeve around the muscles of the leg. During muscle contraction, this fascia helps compress the deep veins more effectively, improving the upward flow of blood.

Groups of veins of lower limb

The veins of the lower limb are divided into three groups:

1. Superficial veins
2. Deep veins
3. Perforating veins

Superficial Veins

• Superficial veins lie in the superficial fascia, just beneath the skin.
• The two main superficial veins are the great saphenous vein and the small saphenous vein.
• These veins have thick walls and contain numerous valves.
• The valves are more numerous in the lower part of the limb than in the upper part, helping to prevent the backflow of blood.

Deep Veins

• Deep veins lie deep to the deep fascia, usually accompanying the arteries.
• Most deep veins are located beneath the muscles.
• They include the medial plantar veins, lateral plantar veins, dorsalis pedis veins, anterior and posterior tibial veins, fibular (peroneal) veins, popliteal vein, femoral vein, and their tributaries.
• Many deep veins accompany arteries as venae comitantes (paired veins running alongside an artery).

Perforating Veins

• Perforating veins connect the superficial veins with the deep veins.
• They contain one-way valves that allow blood to flow from the superficial veins to the deep veins.
• These valves prevent the backward flow of blood from the deep veins into the superficial veins, helping maintain efficient venous return.

Long Saphenous Vine

• The great saphenous vein, also called the long saphenous vein, is the longest vein in the body. It lies in the superficial fascia of the lower limb. Embryologically, it represents the preaxial vein of the lower limb.

Formation

• The great saphenous vein begins on the dorsum of the foot. It is formed by the union of:
  • The medial end of the dorsal venous arch
  • The medial marginal vein of the foot

Course

• The vein ascends in front of the medial malleolus. It then crosses the medial surface of the tibia obliquely. It continues upward just behind the medial border of the tibia. At the knee, it passes along the posteromedial side of the joint. It then ascends on the medial side of the thigh and reaches the saphenous opening in the fascia lata.

Termination

• The great saphenous vein passes through the saphenous opening. It pierces the cribriform fascia and the femoral sheath. Finally, it drains into the femoral vein at the saphenofemoral junction.

Tributaries of the Great Saphenous Vein

Formative Tributaries

• Medial end of the dorsal venous arch
• Medial marginal vein of the foot

Tributaries in the Leg

• Communicating veins from the small saphenous vein
• Communicating veins from the deep veins

Tributaries Just Below the Knee

• Anterior vein of the leg
• Posterior arch vein
• Small veins from the calf

Tributaries in the Thigh

• Accessory saphenous vein
• Anterolateral vein of the thigh

Tributaries Near the Saphenous Opening

Before piercing the cribriform fascia, it receives:

• Superficial epigastric vein
• Superficial circumflex iliac vein
• Superficial external pudendal vein

Last Tributary Before Termination

• Deep external pudendal vein

Key description

Posterior Arch Vein

• The posterior arch vein is a large and constant tributary of the great saphenous vein.
• It drains the posteromedial part of the calf. It begins as a network of small venous arches around the medial ankle. It joins the great saphenous vein just below the knee.

Anterior Vein of the Leg

• This vein ascends upward, forward, and medially across the front of the tibia. It joins the great saphenous vein just below the knee.

Anterolateral Vein of the Thigh

• It begins on the front and lateral side of the lower thigh. It runs upward and medially, crossing the apex of the femoral triangle. It drains into the great saphenous vein.

Accessory Saphenous Vein (Posteromedial Vein of the Thigh)

• The accessory saphenous vein begins on the posteromedial side of the thigh. It joins the great saphenous vein. In some individuals, it forms a communicating channel between the great and small saphenous veins.

Valves of the Great Saphenous Vein

• The great saphenous vein contains about 10–20 valves along its course. These valves ensure one-way flow of blood toward the heart and prevent backflow.

Important Valves

• A valve is present just before the vein pierces the cribriform fascia. Another important valve is located at the junction of the great saphenous vein and the femoral vein. This is called the saphenofemoral valve. A valve in the external iliac vein (the continuation of the femoral vein) helps prevent increased venous pressure from being transmitted to the great saphenous vein.
• In about 20% of individuals, this external iliac vein valve is absent. These individuals have a higher risk of developing varicose veins.

Short or Small Saphenous Vein

• The small saphenous vein, also called the short saphenous vein, is a superficial vein that lies in the superficial fascia of the lower limb.

Beginning

• The small saphenous vein begins below and behind the lateral malleolus.
• It is formed by the union of:
  • The lateral end of the dorsal venous arch
  • The lateral marginal vein of the foot

Course

• The vein passes behind the lateral malleolus.
• It then ascends along the back of the leg, lying lateral to the calcaneal (Achilles) tendon.
• It continues upward in the midline of the posterior calf.
• In the lower part of the popliteal fossa, it pierces the deep fascia.

Termination

• After piercing the deep fascia, the small saphenous vein drains into the popliteal vein.

• In the leg, the small saphenous vein is accompanied by the sural nerve, making the nerve vulnerable during surgical procedures involving the vein.
• In many individuals, the vein gives off an extension called the vein of Giacomini, which continues upward into the posterior thigh and may communicate with the great saphenous vein.
• The small saphenous vein contains multiple valves that help maintain one-way blood flow toward the popliteal vein.

Pseudo-Short Saphenous Vein

• The pseudo-short saphenous veins are enlarged muscular veins that drain the gastrocnemius muscle into the popliteal vein.
• When these veins become dilated, they can resemble varicose veins of the small saphenous vein.
• Because they mimic the appearance of the small saphenous vein, they are called pseudo-short saphenous veins.

Table 18.3: Comparison between long and short saphenous veins

Feature	Great (Long) Saphenous Vein	Small (Short) Saphenous Vein
Formation	Formed by the union of the medial end of the dorsal venous arch and the medial marginal vein of the foot	Formed by the union of the lateral end of the dorsal venous arch and the lateral marginal vein of the foot
Relation to the malleolus	Passes anterior to the medial malleolus	Passes posterior to the lateral malleolus
Number of valves	Usually 10–20 valves	Usually 7–12 valves
Related sensory nerve	Saphenous nerve	Sural nerve
Termination	Drains into the femoral vein at the saphenofemoral junction	Drains into the popliteal vein in the popliteal fossa

Perforating Veins of Lower Limb

• Perforating veins connect the superficial veins with the deep veins. They are called perforators because they pierce the deep fascia. The valves in these veins allow blood to flow only from the superficial veins to the deep veins, preventing backflow.

Types of Perforating Veins

1. Indirect Perforators: Indirect perforators connect the superficial veins to the deep veins through the muscular venous plexuses (muscular veins).
2. Direct Perforators: Direct perforators connect the superficial veins directly with the deep veins, without passing through muscular veins.

Note: The terminal parts of the great saphenous vein and small saphenous vein act as large direct perforators because they open directly into the femoral and popliteal veins, respectively.

Important Perforating Veins

Hunterian (Adductor Canal) Perforator

• Located in the lower part of the adductor canal. Connects the great saphenous vein with the femoral vein.

Boyd’s (Knee) Perforator

• Located just below the knee, close to the medial border of the tibia. Connects the great saphenous vein with the posterior tibial vein.

Lateral Ankle Perforator

• Located at the junction of the middle and lower thirds of the leg. Connects the small saphenous vein with the fibular (peroneal) vein.

Cockett’s Medial Ankle Perforators

• There are three medial perforators on the medial side of the lower leg. They connect the posterior arch vein (a tributary of the great saphenous vein) with the posterior tibial vein.

The three perforators are:

• Upper Cockett perforator: Located at the junction of the middle and lower thirds of the leg.
• Middle Cockett perforator: Located just above the medial malleolus.
• Lower Cockett perforator: Located behind and below the medial malleolus.

Deep Veins

• The deep veins lie beneath the deep fascia and usually accompany the major arteries.
• They are responsible for carrying most of the venous blood from the lower limb back to the heart.

Main Deep Veins

• Femoral vein
• Popliteal vein
• Venae comitantes (paired veins accompanying the arteries), including:
  • Dorsalis pedis veins
  • Anterior tibial veins
  • Posterior tibial veins
  • Fibular (peroneal) veins
• Medial plantar veins
• Lateral plantar veins

Varicose Veins

Definition:

Varicose veins are enlarged, dilated, and tortuous superficial veins that develop due to failure of the venous valves. When these valves become incompetent, blood flows backward and collects in the superficial veins, causing them to become swollen and twisted. Varicose veins are a common feature of chronic venous insufficiency.

Epidemiology:

Varicose veins commonly affect the superficial veins of the lower limbs. They are more frequent in people whose occupations require prolonged standing, such as teachers, doctors, traffic police, bus conductors, and shopkeepers. They are also more common in women than in men because of factors such as pregnancy and hormonal influences.

Causes:

The main cause of varicose veins is incompetence of the venous valves, which allows blood to flow backward (venous reflux). Incompetent perforating veins permit blood to pass from the deep veins into the superficial veins during muscle contraction, increasing pressure in the superficial veins. Similarly, incompetence of the saphenofemoral valve allows blood to reflux from the femoral vein into the great saphenous vein, leading to progressive dilatation and tortuosity of the vein.

Trendelenburg Test

The Trendelenburg test is performed to identify the site of venous valve incompetence in patients with varicose veins. The patient lies down with the affected leg elevated so that the superficial veins empty. The examiner compresses the saphenofemoral junction and asks the patient to stand while maintaining the pressure. When the pressure is released, rapid filling of the varicose veins from above downward indicates incompetence of the saphenofemoral valve, and the test is considered positive. If the veins do not fill rapidly, the test is negative. If pressure over the saphenofemoral junction is maintained for about one minute and the veins gradually fill from below upward, it indicates incompetence of the perforating veins, allowing blood to pass from the deep veins into the superficial veins.

Perthes Test (Tourniquet Test)

The Perthes test is used to assess the patency of the deep veins. A tourniquet is applied around the upper thigh to compress the great saphenous vein without obstructing the femoral vein. The patient is then asked to walk or perform calf muscle exercises. If the deep veins are blocked, the varicose veins become more swollen and painful because blood cannot drain into the deep venous system. This is called a positive Perthes test. If the deep veins are normal and patent, the varicose veins become less prominent or collapse during walking, indicating a negative Perthes test.

Clinical Importance:

Varicose veins may cause aching pain, heaviness, swelling, muscle cramps, itching, and skin discoloration of the affected limb. If left untreated, chronic venous insufficiency may lead to complications such as venous ulcers, particularly around the medial malleolus. Early diagnosis using clinical tests helps determine the site of valve incompetence and guides appropriate treatment.

Lymphatic Drainage of Lower Limb

• Most of the lymph from the lower limb drains into the inguinal lymph nodes.
• The deep structures of the gluteal region and the upper part of the posterior thigh drain into the internal iliac lymph nodes.
• The lymph nodes of the lower limb are divided into superficial and deep groups.

The superficial lymph nodes include the superficial inguinal lymph nodes. The deep lymph nodes include the deep inguinal, popliteal, and anterior tibial lymph nodes.

Superficial Inguinal Lymph Nodes

The superficial inguinal lymph nodes lie in the superficial fascia of the femoral triangle. They are arranged in the shape of the letter “T” and are divided into three groups: the lower vertical group, the upper lateral group, and the upper medial group.

Lower Vertical Group

The lower vertical group consists of 4–5 lymph nodes located along the terminal part of the great saphenous vein. These nodes drain the skin and superficial fascia of most of the lower limb, except the buttock and the area drained by the small saphenous vein, which first drains to the popliteal lymph nodes.

Upper Lateral Group

The upper lateral group consists of 2–3 lymph nodes situated below the lateral part of the inguinal ligament. These nodes receive lymph from the lateral part of the lower anterior abdominal wall below the umbilicus, the buttock, and the flank and back below the level of the umbilicus.

Upper Medial Group

The upper medial group contains 2–3 lymph nodes located below the medial end of the inguinal ligament. They drain the medial part of the lower anterior abdominal wall, the perineum, the external genitalia (except the glans penis and glans clitoris), the anal canal below the pectinate line, the penile (spongy) urethra, the lower part of the vagina below the hymen, and the superolateral part of the uterus through the round ligament.

Deep Inguinal Nodes

The deep inguinal lymph nodes are 4–5 nodes located medial to the upper part of the femoral vein in the femoral triangle.

Node of Cloquet (Rosenmüller)

The node of Cloquet, also called the Rosenmüller node, is the highest deep inguinal lymph node and lies within the femoral canal. It receives lymph from the superficial inguinal lymph nodes, the popliteal lymph nodes, the glans penis, the glans clitoris, and the deep lymphatic vessels of the lower limb accompanying the femoral vessels. The efferent lymphatic vessels from the deep inguinal nodes drain into the external iliac lymph nodes.

Popliteal Lymph Nodes

The popliteal lymph nodes are 6–7 nodes embedded in the fat of the popliteal fossa. One node is usually located at the junction of the small saphenous vein and the popliteal vein, while the remaining nodes lie around the popliteal artery.

These nodes drain the posterior and lateral aspects of the calf, the sole of the foot, and the knee joint. Their efferent lymphatic vessels pass mainly to the deep inguinal lymph nodes, with some also communicating with the superficial inguinal lymph nodes.

Anterior Tibial Lymph Node

The anterior tibial lymph node is an inconstant lymph node, meaning it may not be present in every individual. It is found along the upper part of the anterior tibial artery. This node receives lymph from the anterior compartment of the leg and drains into the popliteal lymph nodes.

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