Structure of the Knee and How It Works

The knee is the largest and most complex joint in the human body. It provides connectivity for the thigh bone or femur and the shin bone or tibia. Made up of bones, muscles, tendons, ligaments, cartilage and synovial fluid, the knee has the ability to bend, straighten and rotate sideways. Read on to understand the structures of the knee, and how it works.

Structure of the Knee

1. Bones of the Knee

The knee is made up of four bones namely femur, tibia, patella and fibula.

  • Femur. This is the longest, largest and strongest bone in the human body. It runs from the hip to the knee where it ends in two rounded knobs known as condyles.
  • Tibia. The second longest bone in the body lies between the knee and the ankle. On the top of its thickened end known as tibial tubercle, tibia flattens into a plateau on which protrudes two menisci. They're crescent-shaped cartilaginous structures that provide stability and shock absorption for the knee.
  • Patella. This triangular shaped bone is located to the front of the knee where it glides along the femoral condyles at the bottom front surface of the femur. It moves when there is knee movement, relieving friction between the bones and muscles.
  • Fibula. This is a thin bone running alongside the tibia between the knee and the ankle.

2. Ligaments in the Knee

Ligaments attach various bones together. Five main ligaments contribute to the stability of the structure of the knee, which are medial collateral, posterior cruciate, anterior cruciate, lateral collateral and patellar ligaments.

  • Medial collateral ligament connects the femur to tibia on the medial side, limiting the knee's sideways movement.
  • Posterior cruciate ligament is the strongest ligament connecting the femur to the tibia. It is located to the rear of the anterior cruciate ligament, inside the knee.
  • Anterior cruciate ligament connects the femur to tibia through the center of the knee; limiting forward and rotational movement of the knee.
  • Lateral collateral ligament connects the femur to the fibula bones, limiting sideways movement.
  • Patellar ligament connects the kneecap to the tibia bone.

3. Tendons in the Knee

Tendons attach muscles to bones. The knee has two main tendons, namely quadriceps and patellar tendons.

  • Quadriceps tendon attaches thigh muscles (quadriceps muscles) to the patella, allowing for straightening of the knee and holding of the kneecap within the patellofemoral groove.
  • Patellar tendon attaches the patellar to the tibia.

4. Cartilage of the Knee

Cartilage is the smooth, white, fibrous tissue covering the extremities of bones where they come into contact with other bones. To some extent, the stability of the structure of the knee and its smooth operation depends on cartilage in three places as follows:

  • Medial meniscus is crescent shaped cartilage inside the knee on the upper surface of the tibia.
  • Lateral meniscus is crescent shaped cartilage on the outer side of the upper surface of the tibia.
  • Articular cartilage covers the ends of any bones forming a joint. In the case of the knee, articular cartilage is located on the ends of femur, tibia and the inner surface of the patella. Lubrication for cartilage is provided by synovial fluid produced by the joint lining (synovial membrane).

5. Muscles Around the Knee

Two main groups of muscles, hamstring and quadriceps keep the knee aligned and stable when in motion or stationary.

  • The hamstring muscle group consists of three muscles located on the rear of the thigh. They help in the movement of the knee from straight to bent position.
  • The quadriceps muscle group consists of four muscles located on the front of the thigh. They support the movement of the knee from bent to straight position.

6. The Joint Capsule

Another structure of the knee is the joint capsule, a fibrous tissue that encapsulates the knee joint. The inside surface of the capsule is soft tissue known as the synovium which secretes synovial fluid, the lubricant that helps the knee joint to operate smoothly.

7. Bursa 

Bursas are fluid-filled sacs responsible for cushioning joints and reduction of friction between muscles, ligaments and tendons. The knee contains 13 bursas located in various places underneath ligaments and tendons. The patella bursa located under the skin to the front of the knee is the most outstanding.

8. Nerves 

The tibial and peroneal nerves are the two main nerves around the knee. The two are formed when the sciatic nerve splits above the knee. The tibial nerve runs along the back of the lower leg while the peroneal nerve runs around the outside of the knee, and continues down the front of the lower leg. Both nerves end up in the foot.

9. Blood Vessels 

The two main blood vessels in the knee area are popliteal artery and popliteal vein. Both run beside the tibial nerve in the back of the lower leg and terminate in the foot. Serious damage to the popliteal artery which supplies blood to the lower leg and foot, will spell an end to the leg.

Ways to Make Your Knees Stronger

Because the knee is one of the most overworked joints in the body, you need to take good care of it so that it serves you well into your old age. You can do this by exercising regularly and leading a healthy lifestyle.

1. Exercises 

Movements of the knee involve the quadriceps and hamstring muscles of the thigh. Other muscles such as the glutes also contribute to the health of your knees. By regularly doing the following exercises that involve stretching and working these muscles, you will strength them and in turn maintain or improve the health of your knees:

  • Walking
  • Skipping Rope
  • Cycling
  • Swimming
  • Yoga Exercises

2.  Lifestyle Changes

Today's lifestyle is notorious for the consumption of inflammatory foods. The result is that more people are suffering from inflammatory diseases including those that are detrimental to the healthy maintenance of the structure of the knee and other joints. But by making the following lifestyle changes, you can stop the inflammation problem and keep your knees healthy:

  • Eat anti-inflammatory foods such as avocados, flax seeds, fish, olive oil and leafy vegetables.
  • Eat vitamin E rich foods such as spinach, peanuts, broccoli, kiwi and mango fruits among others.
  • Cut down on sports and other rough activities that can cause injury to your knees.
  • Eat calcium-rich foods such as milk, cheese, yogurt, leafy vegetables and almonds among others to strengthen your knee and other bones in your body.
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