Lower limb in human body

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Lower Limb

INTRODUCTION

Human beings are unique among the primates in that they have adopted a bipedal mode of locomotion which has produced a substantial advantage over the older, more stable, quadrapedal gait. Bipedalism brings the advantage of a greater range of vision and frees the hands for the use of and for making tools and carrying food. As a result of bipedal locomotion, the weight of the body is transmitted to the lower limb via the pelvis. This has brought about several specialisations in the architecture of the skeleton, joints and muscles of the lower limb. These specialisations will have to be examined as the student proceeds with the dissection of the lower limb. Since the lower limb is an outgrowth from the lateral aspect of the lower part of the trunk, its nerves and blood vessels are drawn out from within the abdomen and pelvis. Consequently, the nerves and vessels entering the front of the thigh pass beneath the inguinal ligament; those to the medial side of the thigh issue through the obturator canal; and those entering the gluteal region traverse the greater sciatic foramen. It must also be borne in mind that the lower limb has undergone rotation during development. Thus, the original (embryonic) extensor or dorsal surface has shifted to the anterior or ventral aspect in the adult. Therefore, the extensor muscles which are now in the anterior compartment of the thigh are supplied by dorsal divisions of the lumbar plexus (femoral nerve L2, 3, 4). Similarly, the adductor muscles which lie on the medial side of the thigh developmentally belong to the flexor compartment and are hence supplied by ventral divisions of the lumbar plexus (obturator nerve L2, 3, 4). The pure flexor muscles, which are now at the back of the thigh, are called the hamstring muscles. These are supplied by ventral divisions of the sacral plexus via branches from the tibial component of the sciatic nerve. In the thigh, the anterior (extensor), medial (adductor) and posterior (flexor) compartments are separated by the medial, posterior and lateral intermuscular septa. Of these, the lateral intermuscular septum is the most well defined. However, all three septa fade away in the lower part of the thigh. Just like in the thigh, the muscles of the leg are also arranged as broad functional groups separated by intermuscular septa. The anterior compartment containing the extensor muscles and the lateral compartment containing the fibular muscles both belong developmentally to the extensor group. Consequently, the common fibular nerve which supplies them is derived from the dorsal divisions of the sacral plexus. Note that the muscles in the posterior compartment are supplied by the tibial nerve. The foot and hand have many similarities, but the hand is a tactile, grasping organ, whereas the functions of the foot are support and locomotion. The foot has evolved from a prehensile ape foot into the sprung arches of humans, one of the most specialised features in the human species.

ANTERIOR ASPECT OF THE THIGH

1. Make the following incisions:

(a)a curved incision along the fold of the groin from the anterior superior iliac spine to the pubic tubercle;

(b) a vertical incision along the medial aspect of the limb from the pubic tubercle to a point 10 cm below the level of the knee; and

(c) extend the lower end of incision

(b) across the front of the leg to its lateral border.

Reflect the skin.

2. Clear away the superficial fascia. As you do so, identify the great saphenous vein behind the medial condyle of the femur and trace it upwards to its entry into the femoral vein. Note that some of the tributaries that drain into the great saphenous vein in the region of the groin are accompanied by superficial arteries arising from the femoral artery.

3. In the superficial fascia are also the superficial inguinal lymph nodes, which are disposed as follows:

(a)in a horizontal set below the inguinal ligament; and

(b) in a vertical chain along the upper end of the great saphenous vein.

4. Note that the cutaneous nerves which supply the front and medial aspect of the thigh come from the femoral nerve. One cutaneous branch of the femoral nerve that you should try to find is the saphenous nerve, which runs along with the great saphenous vein, behind the medial condyle of the femur.

5. Note that the membranous layer of the superficial fascia of the lower anterior abdominal wall extends into the thigh and fuses with the deep fascia along a horizontal line passing laterally from the pubic tubercle. Remove the remains of the superficial fascia in order to expose the deep fascia of the thigh known as the fascia lata. Note the attachments of this fascia to the inguinal ligament and iliac crest in front and on the lateral side. Identify the iliotibial tract, a well defined thickening of this fascia on the lateral side of the thigh. Define its extent between the tubercle of the iliac crest and the lateral condyle of the tibia.

6. Observe a deficiency in the deep fascia around the region of entry of the great saphenous vein into the femoral vein. This deficiency is known as the saphenous opening and is covered by a sieve-like fascia termed the cribriform fascia. Clear away this fascia and note the sharp crescentic margins of the saphenous opening. The centre of this opening lies 3 cm below and lateral to the pubic tubercle.

7. Remove the deep fascia in order to expose the muscles of the front of the thigh but preserve the iliotibial tract. Make an attempt to identify the medial and lateral intermuscular septa.

8. Define the inguinal ligament and identify the muscles below it. From lateral to medial, these are: iliopsoas, pectineus, and adductor longus. The triangular area bounded by the inguinal ligament above, sartorius laterally and the medial border of the adductor longus medially is referred to as the femoral triangle. Clean the following structures within the triangle:

(a)the femoral nerve in the groove between the muscular iliacus and the tendinous psoas;

(b) the femoral artery lying 1 cm medial to the femoral nerve on the psoas tendon; and

(c) the femoral vein lying immediately medial to the artery. Note that the upper 3–4 cm of the femoral vessels are enclosed in a fascial covering called the femoral sheath; this is a funnel-shaped downward prolongation of the fascia iliaca posteriorly and the fascia transversalis anteriorly. Within the femoral sheath, on the medial side of the femoral vein look for a space known as the femoral canal. This has a blind lower end and contains only fat and a lymph node. Examine the boundaries of the mouth of the canal which is known as the femoral ring. Verify that the inguinal ligament is anterior, lacunar ligament is medial, pecten pubis is posterior and femoral vein is lateral to the ring. Clinically, the femoral canal is important since it is the site for femoral hernia.

9. Clean the sartorius and study its attachments. Note that it arises from the anterior superior iliac spine and that it is inserted into the medial surface of the tibia close to the upper end of the bone. Clean the femoral nerve and note that it supplies the sartorius and pectineus muscles.

10. Turn your attention to the femoral artery and note that it has several superficial branches. A major branch is the profunda femoris which arises from the lateral side of the femoral artery 2–5 cm below the inguinal ligament.

1. Trace the profunda femoris artery running behind the adductor longus towards the apex of the femoral triangle where it lies deep to the femoral vessels.

2. Cut the sartorius muscle in its middle so as to expose the adductor canal. Note that the adductor canal is a groove between the vastus medialis anteriorly, and the adductor longus and adductor magnus posteriorly, and is bridged by the sartorius which forms the roof of the canal. Identify the following contents of the canal:

(a)femoral artery and vein;

(b) saphenous nerve; and

(c) nerve to the vastus medialis.

3. Trace the femoral artery and vein downwards and note that they pass through an opening in the adductor magnus to enter the popliteal fossa.

4. Now turn your attention to the extensor muscles which lie in the front of the thigh. Clean them. These are:

(a)the rectus femoris arising from the anterior inferior iliac spine and from above the acetabulum;

(b) the vastus medialis and vastus lateralis lying on either side of the rectus femoris and arising from the medial and lateral aspects of the shaft of the femur respectively; and

(c) the vastus intermedius which lies deep to the rectus femoris and taking origin from the upper two thirds of the anterior and lateral surfaces of the shaft of the femur. Divide the rectus in the middle and reflect the cut parts to see the vastus intermedius. Observe that the extensor muscles are partly inserted into the patella and partly continued down as the ligamentum patellae, which is attached to the tibial tuberosity. The extensor muscles are supplied by the femoral nerve.