Knee Joint

Figure 1: Knee Joint- Bones and ligaments

The Knee joint is a hinge-like synovial joint that connects the femur (thigh bone) to the tibia (shin bone) called as tibiofemoral joint and the kneecap (or patella) meets the femur called as patellofemoral joint.

    The knee joint is the largest joint in our body. It is vulnerable to injury as it bears an enormous amount of pressure while providing flexible movement. When we walk, the load on our knees is equal to 1.5 times our body weight. When climbing stairs it is equal to 3-4 times our body weight. When we squat, the load on our knees increases to about 8 times our body weight!

Major bones involved in Knee Joint:

1. The femur (thigh bone) – the longest bone in the body; the inferior femoral end is in the form of 2 hemispheres joined in front and divided at the backside. This convex and smooth hemisphere are called condyles and covered with articular(hyaline) cartilages.
2. Tibia(shin bone) – runs from the knee to the ankle. The top of the tibia is made up of two slightly concave plateaus (or flat surfaces) which are covered in articular cartilage. Tibia upper end is a little smaller than the femoral lower end and hence there are two C-shaped shock-absorbing cartilages called menisci and it is comprised of fibro-cartilages. Mensci gives stability to the joint and also it acts as a weight-bearing component.
3. Patella(kneecap) – a semi-flat, triangular bone that is able to move as the knee bends. Its main function is to increase the force generated by the quadriceps muscle. The patella also protects the knee joint from trauma. The patella glides within the groove formed between the two femoral condyles called the patellofemoral groove.
4. The contact area between the patella and Femur changes with knee joint position. When Knee is straight, it is minimum and when the knee starts folding the contact area increases and the patella moves down.
5. Fibula - a long, thin bone in the lower leg on the lateral side which runs alongside the tibia from the knee to the ankle. While about 80-90% of the weight is carried by the tibia, the fibula does help to carry some weight as well. Importantly, it serves as an attachment for muscles like the biceps femoris (one of the hamstring muscles), lateral collateral ligament, and also helps to form the ankle joint.

Knee Joint Compartments:

The joint consists of three “compartments” or sections:

1. Medial Compartment (inner half of your knee)
2. Lateral compartment (outer half of your knee)
3. Patellofemoral compartment (behind the knee cap)

Osteoarthritis can affect one, two, or all three compartments.

Figure 2:Knee Joint- Compartments

 

Knee Joint Ligaments, capsules, and muscles:

• There exists the capsule made up of fibrous tissue, which keeps the bony ends near to each other. Inside the capsule, there is Synovial membrane lining which produces synovial fluid and this fluid lubricates the joint and nourishes the cartilage that coats the end of bones in the joint.
• There are fibroelastic bands called ligaments, which offer mobility and stability to the joint. They are the anterior cruciate ligament (ACL), the posterior cruciate ligament (PCL), the medial collateral ligament (MCL), and the lateral collateral ligament (LCL).
• The anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) are two strong, rounded bands that extend from the head of the tibia to the center part of 2 condyles of the femur. The lateral ACL and the medial PCL cross each other in an X formation. ACL limits the sliding of the femur in the backward direction and PCL limits the sliding of the femur in the forward direction.
• Medial Collateral(MCL) attaches medial side femur to the medial side of Tibia and limits the sideways motion.
• Lateral collateral ligament (LCL) attaches lateral side femur to the lateral side of Fibula and limits the sideways motion.
• Near & surrounding to the ligaments there are muscles that help in knee joint movements. The principal muscles involved in the knee joint are the quadriceps and the hamstrings. The quadriceps muscles lie on the top of the femur at the front of the knee. Quads extend (or straighten) the knee joint. Hamstrings are the muscles at the back of the thigh or femur. Hamstrings flex (or bend) the knee. Many other muscles are also concerned with the function of the knee joint.