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How Does The Knee Work?


In this article we’ll look at the knee in more detail, examine how it works and identify the areas where things can go wrong.

The Joint

The knee is one of the largest and most complex joints in the body, it is a pivotal hinge joint. This type of joint permits bend and extension as well as small amounts of internal and external rotation. Due to its limited range of motion and the heavy load it carries the knee joint can be prone to injuries.

Knee bones

The knee joins the thigh to the shin and is made up of 4 bones; femur, tibia, fibula and patella. The femur is the thigh bone which connects to the tibia, the shin bone. The fibula is a smaller bone which runs alongside the tibia and forms the lateral part of the ankle joint. The patella is commonly known as the kneecap and is a triangular piece of bone that sits in a groove at the lower end of the femur.

Tendons explained

Tendons are tough bands of connective tissue connecting the knee bones to the leg muscles that move the joint. Ligaments are made up of tough bands of tissue too but ligaments connect bone to bone. The knee joint has four major ligaments joining the bones together to keep the knee stable. The anterior cruciate ligament (ACL) prevents the femur from sliding backwards onto the tibia and the posterior cruciate ligament (PCL) prevents the femur from sliding forwards onto the tibia.

The medial and lateral collateral ligaments prevent the femur from sliding side to side. The medial collateral ligament (MCL) stabilises the joint, preventing the knee from buckling inwards.

The lateral collateral ligament (LCL) stabilises the knee on the outside of the joint. Two crescent shaped bands of cartilage called the medial and lateral menisci act as shock absorbers between the femur and tibia. They protect the ends of the bones from rubbing on each other and help stabilise the knee further.

Small fluid-filled sacs called, bursae surround the knee joint to keep the joint lubricated.

It provides a cushion between bones and tendons reducing friction and aiding movement.

How the knee works

The knee is a hinge joint but it also has the ability to rotate slightly as it moves. The contraction of muscles at the front of the thigh (quadriceps) straightens the leg, while contraction of the muscles at the back of the thigh (hamstrings) allow the leg to bend at the knee. When you straighten your leg, the quadricep muscles pull on the quadricep tendon, this pulls the kneecap to make the knee extend. When you bend it, the hamstring muscles contract and pull the tibia backwards, causing the knee to flex. The range of movement in the knee depends on certain factors such as soft-tissue restraints and muscle tightness.

Common knee problems

The knee is a complex mechanism, and mechanical devices can fail if placed under excess strain over time. Knee pain can be the result of an accident but many knee problems develop over time. This maybe because parts of the knee are weak or the lubricating pads have become damaged.

ACL tears are one of the most common knee injuries especially in sport. The ACL is crucial for stabilising the knee so if the injury is severe surgery or reconstruction may need to be carried out. The collateral ligaments are also responsible for a number of knee injuries in athletes, tears and sprains are more common in contact sports like football and rugby.

MCL injury is most commonly caused by the twisting of the knee at the same time as the foot being firmly planted on the ground, this is known as valgus stress. MCL injuries also occur in contact sports when a force is applied to the leg, just above the knee.

Persistent knee pain or acute pain when exercising should always be investigated by a medical professional.

If you suffer from knee pain, or want to discuss an injury call us now on 0131 447 2340 to book an appointment with one of our consultants.

Our new knee arthroscopy service is now available at The Edinburgh Clinic with our expert orthopaedic surgeon. For more information or to book an appointment with us, please call 0131 447 2340.

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