Knee Anatomy

Understanding the anatomy of the knee is the basis to understanding how it can go wrong.

The knee joint includes the end of the thigh bone (the femur), the top of the leg bone (the tibia) and the knee cap (the patella). The weight of the body is transferred through the femur, across the knee joint, and into the tibia. There are large muscles in the front of the thigh (the quadriceps) that straighten the knee (extension).

The smaller bone in the leg is the fibula. The knee cap (patella) can be seen in the front of the knee on the side view. The apparent space between the bones is actually occupied by articular cartilage and is called the joint space. Cartilage is not dense enough to be seen on an x-ray.

Basically the knee bends and straightens. That may not seem to need complex anatomy - but in fact it is subtle in terms of the inter-relatedness of the various parts. As the knee bends the various soft-tissue structures need to be able to move too. So there are subtle lubricated spaces which one cannot appreciate from an X-ray or even when the joint is opened during surgery.

How does the knee work?

The knee is the largest joint in the body, and one of the most easily injured. It is made up of the lower end of the thighbone (femur) which rotates on the upper end of the shinbone (tibia), and the knee cap (patella) which slides in a groove on the end of the femur. The knee also contains large ligaments which help control motion by connecting bones and bracing the joint against abnormal types of motion. Other parts of your knee, like cartilage, serve to cushion your knee or help it absorb shock during motion.