The knee is the largest joint and one of the most important joints in the body. It plays an essential role in movement related to carrying the body weight in horizontal (running and walking) and vertical (jumping) directions.
The knee joint joins the thigh with the leg and consists of two articulations: one between the femur and tibia (tibiofemoral joint), and one between the femur and patella (patellofemoral joint). The knee is a modified hinge joint, which permits flexion and extension as well as slight internal and external rotation. The knee joint is vulnerable to injury and to the development of osteoarthritis.
The knee is composed of three functional compartments: the patellofemoral articulation, consisting of the patella, or "kneecap", and the patellar groove on the front of the femur through which it slides; and the medial and lateral tibiofemoral articulations linking the femur, or thigh bone, with the tibia, the main bone of the lower leg. The joint is bathed in synovial fluid which is contained inside the synovial membrane called the joint capsule.
This is a 3D-printable medical STL file of normal left knee joint converted from a CT scan dataset of a 75-year old female patient (STS-016).