Knee Anatomy

The knee serves an essential role in the body’s function.  As the largest joint in the body, the knee must bend, straighten, twist, and rotate all while providing support.  There are a number of structures comprising the knee, including bones, ligaments, muscles, cartilage, and the joint capsule.

There are four primary bones important to knee function:  the femur, tibia, fibula, and patella.  The femur and tibia meet to form the main knee joint, and the patella (or kneecap) joins the femur to form the patellofemoral joint.

There are also four ligaments in the knee joint, which contribute to knee stability:  the Medial Collateral Ligament (MCL), the Lateral Collateral Ligament (LCL), the Anterior Cruciate Ligament (ACL), and the Posterior Cruciate Ligament (PCL).  The collateral ligaments are the ligaments on either side of the knee joint, while the cruciate ligaments cross within the joint.

The knee has two main muscle groups.  Knee extension is achieved by contracting the quadriceps muscles, while the hamstrings flex the knee joint and provide stability.

The surfaces of the bones within the knee joint are covered with a layer of cartilage, which allows the bones to smoothly glide against each other.  Between these cartilage surfaces are the lateral meniscus and medial meniscus which act as cushions in the knee joint.

The joint capsule surrounds the entire knee. Inside the capsule are the synovial membrane, which provides nourishment to all the surrounding structures, the infrapatellar fat pad,and the bursae which function as cushions to exterior forces on the knee.