Knee

From ArticleWorld

The knee is a complex joint that is important in establishing the gait particular to humans. It is formed by the distal aspect of the femur and the proximal portion of the tibia. The fibula is the parallel bone to the tibia but does not form an articular surface with the femur.

Anatomy

The skeletal knee is formed by the articular surfaces of the glenoids of the distal femur and matching depressions in the proximal tibia. The knee cap or “patella” is a disc-like sesamoid bone that is encapsulated within the tendons of the lower anterior thigh and the patellar ligament on its lower surface. The connection between the distal femur and the patella is actually a joint surface called the femoro-patellar joint.

The joint would not function well at all without its supporting joint capsule, menisci and its ligaments. The joint capsule surrounds the joint and contains the lubricating synovial fluid. The posterior cruciate ligament and the anterior cruciate ligament are generally not visible to the outside. The medial collateral ligament and the lateral collateral ligaments are the two ligaments on the sides of the joint. There are several other smaller supportive ligaments.

The menisci are half moon-shaped cartilaginous portions of the inside of the knee joint itself. They are well lubricated and protect the bones from actually touching each other.

Function

The knee is able to flex via the hamstring muscles and extend via the quadriceps muscles on the top of the thigh. One can also lock and unlock the knee. The knee has limited ability to rotate.

Conditions

The complexity of the knee joint makes it an easy target for injury. Ruptures of the anterior cruciate ligament or a tear in the medial meniscus are common athletic injuries to the knee. A sports injury or fall can cause the patella to pull away from the medial patellar retinaculum that keeps it in place and can dislocate to the outside. Over time, the menisci of the knee can wear away leading to a painful knee and the eventual necessity of having a knee replacement. The patella can fracture due to a direct fall onto the patella.

There are several bursae, or sacs of lubricating fluid, that normally allow for the knee to move smoothly. In some cases, however, one of the bursae can become inflamed and fill with blood and fluid. One common condition related to this is called a “housewife’s knee”, or what is known as prepatellar bursitis.