Anatomy of Torn Cartilage and Other Knee Injuries

Anatomy of Torn Cartilage and Other Knee Injuries

The human knee is a very complicated joint. Two major bones come together at the knee -- the femur (thigh bone) and the tibia -- (shin bone). There is a third bone located at the knee -- the patella (knee cap), but it does not participate in the joint between the femur and the tibia. The lower end of the femur has two side-by-side convex curved surfaces, while the upper end of the tibia has two side-by-side concave curved surfaces. The convex surfaces on the femur are obviously designed to fit into the concave surfaces on the tibia. But there are several things located in between.

First of all, both the lower end of the femur and the upper end of the tibia are covered with a layer of cartilage, called articular cartilage. Secondly, there are two ring-like pads of cartilage inserted between the articular cartilage of the femur and the articular cartilage of the tibia. One of these is located between the curved surfaces on the medial side (closer to the midline of the body) of the knee and is called the medial meniscus. The other one is located between the curved surfaces on the lateral side (farther from the midline of the body) of the knee and is called the lateral meniscus. Thirdly, there is synovial fluid lubricating all of these cartilage surfaces.

There are also many ligaments associated with the knee. Ligaments are cords of connective tissue which pass from one bone to another across a joint. Their function is to make the joint stronger. Two of these knee ligaments form an X in the area between the medial meniscus and the lateral meniscus. They are called cruciate ligaments, from the latin word for an X. The anterior cruciate ligament (ACL) begins on the middle of the front of the tibia and attaches near the back of the femur. The posterior cruciate ligament (PCL) begins near the middle of the back of the tibia and attaches near the front of the femur.

Two other ligaments of the knee are called collateral ligaments. The medial collateral ligament (MCL) begins on the medial side of the femur and attaches on the medial side of the tibia. The lateral collateral ligament (LCL) begins on the lateral side of the femur and attaches on the lateral side of the tibia. Two more knee ligaments are called popliteal ligaments. They both begin on the back of the femur and provide strength to the back of the knee. The patellar ligament begins at the patella (knee cap) and attaches to the front of the tibia. It adds strength to the front of the knee. There are also other ligaments associated with the knee.

One type of knee injury is called a torn cartilage. This refers to a tear in either the medial meniscus or the lateral meniscus. The medial meniscus is much more likely to be torn than the lateral meniscus. The reason for this is that the medial collateral ligament (MCL) is actually attached to the medial meniscus. The anterior cruciate ligament (ACL) is also attached to the medial meniscus. If the knee is hit from the side or twisted, the force pulls on the medial collateral ligament (MCL), which in turn pulls on the medial meniscus, which in turn pulls on the anterior cruciate ligament (ACL). As a result, the 2 ligaments may stretch or tear. Since the meniscus is composed of cartilage, it cannot stretch; so it tears.

A torn lateral meniscus is much less likely to occur, but it is not impossible. The lateral meniscus is not attached to the lateral collateral ligament (LCL), but it is attached to the posterior cruciate ligament.

Another type of knee injury is a dislocation. This refers to a situation in which the upper end of the tibia is pushed out of its normal position, directly under the lower end of the femur. The tibia could be displaced in any direction -- forward, backward, to the medial side, or the the lateral side, or it could be twisted in place. With a dislocation, there is the possibility of damage to any of the structures associated with the knee or to any of the blood vessels in the knee area.