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Anterior Compartment of the Thigh Anatomy


Anterior Compartment of the Thigh Anatomy
The anterior compartment is the largest in the thigh, occupying the region between the inguinal ligament and the knee. Lateral and anteromedial intermuscular septa separate the contents from the posterior (hamstring) and medial (adductor) compartments, respectively (Fig. 6.2). The anterior compartment (Fig. 6.12) contains quadriceps femoris, sartorius and the tendon of iliopsoas, and is innervated by the femoral nerve. The femoral artery and vein, the principal vessels of the lower limb, traverse the compartment and leave via the opening in adductor magnus to gain the popliteal fossa.


Subcutaneous tissue (superficial fascia)
The subcutaneous tissue contains the great (long) saphenous vein and its tributaries with their accompanying arteries, superficial inguinal lymph nodes and cutaneous nerves. The great saphenous vein ascends on the medial side of the thigh (Fig. 6.11) and passes through the saphenous opening in the fascia lata to empty into the femoral vein. The great saphenous vein drains the superficial tissues of the entire limb except the lateral side of the leg and foot. Near its termination, the vein receives tributaries, which drain the buttock, the perineum and the abdominal wall below the umbilicus. These tributaries are accompanied by corresponding branches of the femoral artery. The superficial inguinal lymph nodes, often palpable in the living, lie just distal and parallel to the inguinal ligament and adjacent to the termination of the great saphenous vein (Fig. 6.11). These nodes receive lymph from the same superficial tissues as those drained by the great saphenous vein and its tributaries. Efferent lymphatics from the superficial nodes pass through the fascia lata and drain into the deep inguinal nodes within the femoral triangle and femoral canal, where nodes are a focal point in lymphatic drainage of the lower limb (p. 257).
The lateral cutaneous nerve of the thigh (L2 & L3) (Fig. 6.17) pierces the inguinal ligament close to the anterior superior iliac spine, where it may become entrapped, causing pain in the thigh (meralgia paraesthetica). It supplies skin as far as the knee. The intermediate and medial cutaneous nerves of the thigh arise from the femoral nerve and supply the anterior and medial surfaces of the thigh. Usually, the obturator nerve gives a cutaneous supply to the medial side of the thigh. The femoral branch of the genitofemoral nerve (L1 & L2) passes beneath the inguinal ligament to supply skin over the femoral triangle, and the ilioinguinal nerve emerges through the superficial inguinal ring to supply the adjacent medial aspect of the thigh.

Fascia lata
The fascia lata (deep fascia) completely invests the thigh, providing attachment for muscles and associated intermuscular septa in the anterior compartment. It attaches superiorly to the inguinal ligament and iliac crest, and inferiorly is continuous with the deep fascia of the leg. Below and lateral to the pubic tubercle is the saphenous opening, which transmits the terminal part of the long saphenous vein.
Over the lateral aspect of the thigh, the fascia lata is particularly thick, forming the iliotibial tract. Gluteus maximus and tensor fasciae latae are attached to its upper part (Fig. 6.30).
 
Quadriceps femoris. Vastus intermedius is partially revealed by removal of rectus femoris. Pectineus and adductors longus and brevis have been excised.
Fig. 6.13 Quadriceps femoris. Vastus intermedius is partially revealed by removal of rectus femoris. Pectineus and adductors longus and brevis have been excised.


Muscles
Quadriceps femoris
The four parts of quadriceps femoris, namely rectus femoris, vastus lateralis, vastus intermedius and vastus medialis, cover the front and sides of the femur (Figs 6.12, 6.13 & 6.14). Rectus femoris is attached by a straight head to the anterior inferior iliac spine and by a reflected head to the ilium above the acetabulum.
Vastus lateralis attaches to the intertrochanteric line, the lateral lip of the linea aspera and the lateral supracondylar ridge of the femur (Figs 6.15 & 6.16). Vastus intermedius attaches to the upper two thirds of the anterior and lateral surfaces of the femoral shaft, while vastus medialis anchors to the spiral line and medial lip of the linea aspera. Distally, these four muscles form a common tendon, which attaches to the upper border (base) of the patella. From the lower border (apex) of the patella, the tendon continues as the patellar ligament (Fig. 6.75) to attach to the tibial tubercle.
Quadriceps femoris is a powerful antigravity muscle, extending the knee joint during standing, walking and running. In addition, rectus femoris flexes the hip. The lower fibres of vastus medialis stabilize the position of the patella (p. 300). Quadriceps femoris is supplied by branches of the femoral nerve.
Sartorius
This strap­like muscle is attached proximally to the anterior superior iliac spine and descends obliquely across the thigh (Fig. 6.12), crosses the posteromedial side of the knee and, with gracilis and semitendinosus, attaches to the upper end of the subcutaneous surface of the tibia (Fig. 6.79). Sartorius flexes and laterally rotates the hip and flexes the knee. It is supplied by the femoral nerve.

Femoral triangle
The femoral triangle occupies the upper medial part of the anterior compartment of the thigh. Its upper boundary is the inguinal ligament; its lateral limit is the medial border of sartorius and its medial boundary is the medial border of adductor longus (some authors use the lateral border in their definition). The roof is fascia lata and the floor comprises iliopsoas, pectineus and adductor longus (Fig. 6.17). The triangle contains the femoral vessels and nerve, and the deep inguinal lymph nodes.

Adductor (subsartorial) canal
This canal is an intermuscular space linking the femoral triangle with the popliteal fossa. Triangular in cross­section, it lies beneath sartorius, occupying the groove between vastus medialis and adductor longus, and at its lower end adductor magnus (Fig. 6.14). Through the canal run the femoral artery and vein and nerve to vastus medialis and the saphenous nerve (Fig. 6.18).

Fig. 6.17 Boundaries and floor of the femoral triangle.

Femoral vessels
The femoral artery, a continuation of the external iliac, is the main artery of the lower limb. It enters the anterior compartment behind the midpoint of the inguinal ligament where it is relatively superficial, easily palpable and accessible for catheterization to perform arteriograms. It is also vulnerable to penetrating or stab wounds. It descends through the femoral triangle (Fig. 6.19) and the adductor canal and continues through the opening in adductor magnus as the popliteal artery (p. 274).
The femoral artery or its main branches supplies all three compartments of the thigh. Subcutaneous branches of the artery traverse the saphenous opening or pierce the fascia lata to accompany the superficial veins in the groin (Fig. 6.11). The largest deep branch is the profunda femoris artery (Fig. 6.20), which arises from the posterolateral aspect of the femoral artery about 4 cm below the inguinal ligament and runs distally behind the femoral artery, leaving the triangle by passing between pectineus and adductor longus. The profunda femoris and its perforating branches pass through the adductor muscles and contribute to the anastomosis in the posterior compartment of the thigh. One of the perforating arteries gives a large nutrient branch to the femur.
Close to its origin, the profunda femoris artery usually gives medial and lateral circumflex femoral branches (Fig. 6.20). The medial circumflex artery winds round the medial aspect of the femur between iliop­ soas and pectineus to join the cruciate anas­ tomosis (p. 271), and the lateral circumflex artery encircles the femur, passing laterally deep to sartorius and rectus femoris.
The femoral vein is the continuation of the popliteal vein at the opening in adduc­ tor magnus. In the adductor canal, it lies behind the femoral artery and continues through the femoral triangle, lying medial to the artery (Fig. 6.19). Passing deep to the inguinal ligament the femoral vein becomes the external iliac vein. Tributaries of the femoral vein, except the great saphenous vein, correspond to the branches of the femoral artery.
Femoral sheath
The femoral artery and vein are invested in a thick fascial sleeve, the femoral sheath, derived from the transversalis and iliac fasciae. The sheath passes deep to the inguinal ligament and tapers inferiorly, blending with the adventitia of the vessels about 2.5 cm distal to the ligament.
Two vertical septa divide the sheath into three compartments. The femoral artery lies laterally, while the femoral vein occu­ pies the intermediate compartment. The medial compartment is called the femoral canal (Fig. 6.20) and contains fat and lymph nodes. The upper limit of the femoral canal is the femoral ring (Fig. 4.23), an aperture bounded in front by the inguinal ligament and behind by the superior ramus of the pubis, while laterally lies the femoral vein and medially the lacunar ligament. A femoral hernia descends through the femoral ring to enter the femoral canal.

Femoral nerve
The femoral nerve (L2, L3 & L4) enters the thigh beneath the inguinal ligament, lying on iliopsoas lateral to the femoral sheath (Fig. 6.19). After a brief course in the femoral triangle, it divides into several superficial and deep branches. The superficial branches are the intermediate and medial cutaneous nerves of the thigh and the nerves to sartorius and pectineus. The deep branches include the nerves supplying rectus femoris and the vasti, and the saphenous nerve, which enters the adductor canal.

Deep inguinal lymph nodes
The deep inguinal lymph nodes lie in the femoral triangle medial to the femoral vein.
They receive lymph from the superficial inguinal nodes and from all parts of the limb deep to the investing fascia. They also drain the glans of the penis or clitoris. Efferent vessels pass proximally through the femoral canal to reach the external iliac nodes.


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