HUMAN ANATOMY LOWER LIMB, 1.lntroduction

HUMAN ANATOMY

LOWER LIMB,

1.lntroduction

The lower limb in its basic structure is similar to the upper limb because both of them formerly (as in animals) were used for locomotion. Each limb has a girdle, hip girdle for lower limb or shoulder girdle for upper limb, by which it is attached to the axial skeleton.

The girdle supports three main segments of the limb, a proximal thigh or arm, a middle leg or forearm and a distal foot or hand. The similarity between the two limbs is not only outward, but to a great extent it is also found in the bones, joints, muscles, vessels, nerves and lymphatics.

However, with the evolution of erect or plantigrade posture in man, the two limbs despite their basic similarities have become specialized in different directions to meet the new functional needs. 

The emancipated upper limb is specialized for prehension and free mobility whereas the lower limb is specialized for support and locomotion. In general, the lower limbs attain stability at the cost of some mobility, and the upper limbs attain freedom of mobility at the cost of some stability. 

Thus the lower limbs are bulkier and stronger than the upper limbs (Fig. 1.1). 

A few of the distinguishing features of the lower limbs are listed below.

1 During early stages of development, the lower limb buds rotate medially through 90 degrees, so that their preaxial or tibial border faces medially and the extensor surface forwards (Fig. 1.2). The upper limb buds, on the other hand, rotate laterally through 90 degrees, so that their preaxial or radial border faces laterally and the extensor surface backwards

(Fig. 1.1).

2 The antigravity muscles in the lower limb are much better developed than in the upper limb because they have to lift the whole body up during attaining the erect posture and also in walking up the staircase.

These muscles are the gluteus maximus, extensor of hip; the quadriceps femoris, extensor of knee and the gastrocnemius and soleus, plantar flexors of ankle at the back of leg. They have an extensive origin and a large, bulky, fleshy belly.

The distal end or insertion of the muscles of lower limb moves only when feet are off the ground; this is known as the action from above. But when feet are supporting the body weight, the muscles act in reverse from below, i.e. the proximal end or origin moves towards the distal end or insertion. This is typically seen while rising up from a sitting posture, and in going upstairs. Maintenance of posture in erect attitude, both at rest and in walking, running, etc. also involves the reverse action when th

antagonist muscles must balance against each other. Reverse muscular actions are far less common in the upper limb.

The postaxial bone or fibula of the leg does not take part in the formation of knee joint. Patella or knee cap is a large sesamoid bone developed in the tendon of quadriceps femoris. It articulates with the lower end of femur anteriorly, and takes part in the formation of knee joint.

The foot in lower primates is a prehensile organ. The apes and monkeys can very well grasp the boughs with their feet. Their great toe can be opposed over the lesser toes. In man, however, the foot has changed from a grasping to a supporting organ. In fact, foot has undergone maximum change during evolution. 

The great toe comes in line with the other toes, loses its power of opposition, and is greatly enlarged to become the principal support of the body (Fig. 1.1). 

The four lesser toes, with the loss of prehensile function, have become vestigial and reduced in size. The tarsal bones become large, strong and wedge-shaped, which contribute to the stable support on one hand, and form the elastic arches of the foot on the other hand. 

The small and insignificant heel of the grasping primate foot becomes greatly enlarged and elongated to which is attached the tendocalcaneus that can lift the heel in walking. The bony alterations are associated with numerous ligamentous and muscular modifications which aim at the maintenance of the arches of foot. Certain diseases, like varicose veins and Buerger's disease, occur specifically in the lower limb. The developmental deformities of the foot like talipes equinovarus are more common than those of the hand.

Reloted Terms

L The hip bone is made up of three elements, ilium, pubis and ischium, which are fused at the acetabulum. Two hip bones form the hip gir dle which articulates posteriorly with the sacrum at the

sacroiliac joints. The bony peksis includes the two hip bones, a sacrum and a coccyx. Hip joint is an articulation between the hip bone and femur.

2 The gluteal region, overlying the side and back of the pelvis, includes the hip and the buttock which are not sharply distinguished from each other. Hip or coxa is the superolateral part of the gluteal region presented in a side view, while thebuttock or natis is the inferomedial rounded bulge of the region presented in a back view.

3 The junction of thigh and anterior abdominal wall is indicated by the groove of groin or inguinal region. The gluteal fold is the upper limit of the thigh posteriorly.

4 Ham or poples is the lower part of the back of thigh and the back of the knee.

5 Calf ot sura is the soft, bulky posterior part of the leg. The bony prominences, one on each side of the ankle, are called the malleoli. These are formed by the lower ends of tibia and fibula.

6. The foot or peshas an upper surface, galled the dorsal surface, and a lower surface, called tl:re sole ot plantar surface. Sole is homologous with the palm of the hand.

he line of gravity passes through cervical and lumbar vertebrae. Lr the lower limbs, it passes behind the hip joint and in front of knee and ankle joints (Fig.1.3).