The important structures of the knee are bones, ligaments, tendons, meniscus and cartilage.

The femur is the bone of the thigh. In the lower leg there are two bones, the larger is the tibia, and the smaller is the fibula. The patella (kneecap) is the bone on the anterior aspect of the knee. The femur articulates with the tibia and the patella to form the knee joint. Although the fibula is not inside the knee joint, it is very important because it provides the attachment to several structures i.e. ligaments and muscles.

A ligament is a fibro-elastic structure that connects bones together. Inside the knee, there is one anterior and one posterior cruciate ligament. On the outside, are the collateral ligaments, one is on the internal aspect of the knee (medial collateral ligament) and the other is on the external aspect of the knee (lateral collateral ligament).

The ligaments are the primary stabilizers of the knee joint, this means that the ligaments are the most important structures controlling the knee in athletic activities. Ligaments are the most common structures to be injured in sport due to the abnormal stresses of twisting and stopping.

A tendon is a fibro-elastic structure that connects muscles to bone. In the knee joint there are the quadriceps and the patellar tendon unit. This unit connects the quadriceps muscles to the patella (kneecap) and then to the tibial tubercle. This is also called the extensor mechanism, and extends the knee. The hamstring tendons on the medial side and biceps tendon on the lateral side flex the knee.

The menisci are "C" shaped fibro-cartilaginous structures that separate the tibia and femur. There are two menisci in each knee joint. The meniscus is the "shock absorber" and also helps to provide stability for the knee.

The articular cartilage is the slick teflon like material that covers the ends of the bones in the joints.