Bones
The bones of the knee are the femur (thigh bone), tibia (shin bone), and patella (kneecap). The femur and tibia meet to form a hinge with the patella in front of these two bones protecting the joint. The patella slides up and down in a groove in the femur (the femoral groove) as the knee is bent and straightened.
Ligaments
Ligaments hold the knee together and give it stability. The medial (inner) collateral ligament (MCL) and outer (lateral) collateral ligament (LCL) limit sideways motion of the knee. The posterior and anterior cruciate ligaments (PCL and ACL) limit forward motion of the knee bones, keeping them stable.
Cartilage
Two structures known as menisci sit between the femur and the tibia and act as cushions or shock absorbers for the knee. A torn meniscus is often referred to as “torn cartilage.” Menisci are one of two types of cartilage in the knee. The other type, articular cartilage, is a smooth and very slick material that covers the end of the femur, the femoral groove, the top of the tibia, and the underside of the patella. This articular cartilage allows the bones to move smoothly.
Tendons
Tendons connect muscle to knee. The quadriceps muscles on the front of the thigh are connected to the top of the patella by the quadriceps tendon, which covers the patella and becomes the patellar tendon. The patellar tendon then attaches to the front of the tibia. The hamstring muscles in the back of the leg attach to the tibia at the back of the knee. The quadriceps muscles straighten the knee and the hamstring muscles bend the knee.
Bones, ligaments, cartilage, and tendons all work together to build a healthy knee.
Disorders of the Knee
Knee Anatomy
The largest joint in the body - the knee - is also one of the most complex. The knee can be described as a modified hinge joint, similar to the hinge on a door. However, the knee not only bends back and forth like a hinge, it has a complex rotational component that occurs with flexion and extension of the knee.
The knee is a major weight-bearing joint that is held together by muscles, ligaments, and other important soft tissue. Cartilage is the material inside the joint that provides shock absorption to the knee during weight-bearing activities such as walking or stair climbing.
Below is an illustration of the knee anatomy with its major bones, ligaments, and muscles appropriately labeled.
Traumatic injury to the knee
The knee, while relatively stable, can be injured in any number of ways, including during sports, a fall or a collision. The quick and unexpected twisting or reposition of the joint can damage the cartilage or ligaments. In many cases it is possible to repair this damage by repairing, restoring or replacing the cartilage.
Osteoarthritis
The most common type of arthritis, osteoarthritis, generally develops from "wear and tear" of the cartilage and lubricating surfaces of the bones that connect at the joint. As we age, many of us will develop degenerative arthritis of one or more of our joints. This arthritis is characterized by destruction of the natural cushioning and lubricating surfaces of the joint and may be accompanied by bony overgrowth (bone spurs). In the most severe cases, all the cartilage can wear away and there will be bone-on-bone contact. These severe cases are more commonly treated with knee replacement rather than cartilage restoration.
Avascular necrosis
Characterized by localized bone death, avascular necrosis results from disruption of blood flow to the bone. The bone death may be painful and usually causes the bone to collapse, which can lead to joint destruction and arthritis. In some cases cartilage restoration techniques can be used to treat this disorder to avoid the need for knee replacement.
Rheumatoid (inflammatory) arthritis
An autoimmune disorder characterized by chronic inflammation of the affected joints, rheumatoid and inflammatory arthritis may involve multiple joints and can occur at any age. The inflammatory process of rheumatoid or inflammatory arthritis swells the cartilage, muscles, tendons and ligaments which can misshape the joints, erode the cartilage and eventually lead to destruction of bone. Most of these cases are candidates only for joint replacement when medical management fails
