Several bones meet to form the knee joint; it consists of the femur, tibia and patella. These bones are held together by ligaments, which connect two bones to each other, and tendons, which connect a muscle to a bone.
BONES
Femur (Thigh Bone)
The femoral condyles are the two rounded prominences at the end of the femur; they are called the medial and the lateral femoral condyle, respectively. The motions of the condyles include rocking, gliding and rotating. Any abnormal surface structure or cartilage damage can lead to cartilage breakdown and arthritis (loss of cartilage padding).
Tibia (Shin Bone)
The Tibia meets the Femur at the knee in two areas on which the Femur rides. This area called the Tibial Plateau is divided into a medial (inside of your knee) and a lateral (outside) part.
Patella (Knee Cap)
The Patella is a bone that lies within the quadriceps tendon. It rides in the shallow groove over the front part of the Femur called the Trochlea. The Patella acts as a lever arm to help the quadriceps muscle extend the knee.
CARTILAGE
Articular Cartilage covers the ends of these bones at the knee joint and is also called hyaline cartilage. This glistening white substance has the consistency of firm rubber but is actually a mixture of collagen and special large, sponge-like molecules all maintained by living cartilage cells (chondrocytes). With normal joint fluid for lubrication, the surface is more slippery than ice on ice and allows smooth and easy knee joint motion.
Meniscus cartilage is the other type of cartilage in the knee and is made of a substance called fibrocartilage. There are two of these C-shaped pads in each knee, one on the medial (inside) part, and one on the lateral (outside) part. They are attached to the tibia and lie between the tibial plateau and the femoral condyle to cushion the forces of walking, jumping and running. They accomplish this by distributing joint forces over a larger area of the joint -- transferring force from the curved femoral condylar margins to the flatter tibial plateaus. If the meniscal cartilage is injured, it might have to be removed or repaired arthroscopically. If the entire meniscus is lost due to injury and/or surgery, the articular cartilage of the joint is exposed to much higher stresses and starts to break down, resulting in arthritis.
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