The lower extremity refers to the human leg, including the gluteal or hip region, thigh and foot. However, the exact definition of lower extremity in the human anatomy basically refers to that portion of your lower limb which extends from your knee till the ankle. Hence, the term lower extremity is the scientific and medical term for ‘leg.’The basic functions of your legs includewalking, running, standing, kicking, jumping and other similar activities. Legs constitute a reasonable and substantial portion of your body mass.

Lower Extremity Anatomy: Parts and Functions

Your leg comprises of four main components: one girdle that is formed by your hip bones, thethigh, the calf and your foot. It is a special body part for supporting your body weight and is used for locomotion. It conveniently adapts to gravity.

1. Bones and Joints

• Your upper leg starts at your hip and moves down towards your knee. There is one bone in that region, which is known as the ‘femur.’ It is your body’s largest bone. The head of the femur forms the round ball of the ‘ball and socket’ joint of the hip. Similarly, its base makes up a portion of your knee.
• Your lower leg comprises of two main bones: tibia and fibula. Tibia is your leg’s second biggest bone. It joins with the femur for forming the knee. Yet, the Fibula is another bone in your lower leg. It is attached to your tibia beneath the knee’s joint.
• The kneecap (patella) bone lies in the front of your knee and is in the center of the lower extremity. Your knee is basically a hinge joint in your leg that joins all the bones in your lower and upper leg. Evidently, it is your body’s largest joint. Your knee is the point where your femur in your upper leg connects to the fibula and tibia bones in your lower leg.  
• The ankle joint (or talocrural joint) is a hinge-typed joint and it’s formed by the bones of the leg and the foot – the fibula, tibia and talus. It contains seven bones along with several other structures. Your ankle flexes and rotates your foot that is essential for balance and movement.
• Your foot is a very complicated structure comprising over 33 joints and 26 bones at your leg’s lowest portion. Your foot’s structure resembles that of your hand. However, as your foot withstands more weight and pressure, it is sturdier and stronger, but less moveable.

2. Muscles

The quadriceps and hamstringsare two of the most important muscles in your upper leg. Hamstrings are the three main muscles at your thigh’s back that affects the ‘knee and hip’ movement. Your quadriceps are the leanest and strongest muscles in your body. They are a group of four muscles at your thigh’s front that work for extending the lower leg and knee.

Interestingly, around 20 muscles exist in your lower leg. They are responsible for almost every action of your leg, from raising it to wiggling your toes. Most of the muscles that control the foot movements start as far up as your knee’s back and extend downwards towards your foot.

3. Ligaments and Tendons

Your knee joint comprises of several ligaments, protective elements and tendons, such as bursa and cartilage. These protective and connective tissues keep your bones in their respective places. Also, they prevent the bones from overlapping against one another while enabling your knee joint to twist and flex slightly.

The famous ‘Achilles’ tendon is the most noteworthy structure in your lower extremity anatomy. It joins three muscles: calf, soleus and plantaris to your heel bone. The Achilles tendon stores all the essential elastic energy required for jumping, running and several other physical activities.

4. Nerves

The nerves in your leg transmit messages to your brain as well as the indications of movement, pain, heat and cold. Your sciatic nerve is your leg’s major nerve and in the lower extremity anatomy, it’s called peroneal nerve. It starts in your lower back region and runs downwards to your lower leg. Other important and major nerves in your leg includemedial plantar nerve, lateralplantar nerve,and tibial nerve. Nerves in foot help keep balance both when moving and at rest and also helps to move the body.

5. Arteries and Veins

Two common iliac arteries move down your leg, one in each leg. They branch out into the external and internal iliac arteries that supply blood filled with oxygen and nutrients to the other branches, such as your femoral artery. Your femoral artery is the thigh’s major artery. It starts branching into several smaller arteries quickly as your blood moves down towards your toes and their tips. Other major and substantial arteries in your lower extremity anatomy include:

• Popliteal Artery: It is your femoral artery’s branch. Your popliteal artery further branches down for supplying blood to your thigh, calf and knee. This artery ends at your posterior and anterior tibial arteries.
• Posterior Tibital Artery: It is a branch of your popliteal artery that supplies oxygen rich blood to your leg and foot’s sole. It runs all the way on your leg’s inside and is escorted by your posterior tibial vein.
• Anterior Tibial Artery: It is the second branch of your popliteal artery. Furthermore, it originates from your knee’s back and supplies oxygen rich blood to your foot’s and leg’s muscles.
• Peroneal Artery: It is your posterior tibial artery’s largest branch that supplies oxygen blood and nutrients to the back and outside of your calf muscles and ankle. It finishes off all your lateral calcaneal artery.
• Plantar Arteries: These arteries comprise of the deep, medial and lateral plantar arteries make a looping web all across your foot. They move down towards every toe and meet with your dorsalis pedis artery.
• Dorsalis Pedis Artery: It is the artery that provides blood to your foot’s surface. It is your anterior tibial artery’s continuation. This artery is accompanied by your dorsalis pedis vein.

Hitherto, the veins in your leg return the deoxygenated blood to your heart from the legs, like they do in the entire body. Normally, veins run precisely the same course taken by your arteries. The essential veins of your leg comprise of the external and internal iliac veins, saphenous vein, tibial vein, femoral vein, popliteal vein as well as your foot’s venous arch.