The knee is a complex joint made up of different structures including bones, tendons, ligaments and muscles. They all work together to maintain normal function and provide stability to the knee during movement.
Having a well-functioning healthy knee is essential for our mobility and ability to participate in various activities. Understanding the anatomy of the knee enhances your ability to discuss and choose the right treatment procedure for knee problems with your doctor.
The Knee is a hinge joint made up of two bones, the thigh bone (femur) and the shinbone (tibia). There are two round knobs at the end of the femur called femoral condyles which articulate with the flat surface of the tibia called the tibial plateau. The tibial plateau on the inside of the leg is called the medial tibial plateau, and on the outside of the leg, it is called the lateral tibial plateau.
The two femoral condyles form a groove on the front (anterior) side of the knee called the patellofemoral groove. A small bone called the patella sits in this groove and forms the knee cap. It acts as a shield and protects the knee joint from direct trauma.
A fourth bone called the fibula is the other bone of the lower leg. This form a small joint with the tibia. This joint has very little movement and is not considered a part of the main joint of the knee.
Articular Cartilage and Menisci
The tibial plateau on the inside of the leg is called the medial tibial plateau, and on the outside of the leg, it is called the lateral tibial plateau.
Movement of the bones causes friction between the articulating surfaces. To reduce this friction, all articulating surfaces involved in the movement are covered with a white, shiny, slippery layer called articular cartilage. The articulating surface of the femoral condyles, tibial plateaus and the back of the patella are covered with this cartilage. The cartilage provides a smooth surface that facilitates easy movement.
To further reduce friction between the articulating surfaces of the bones, the knee joint is lined by a synovial membrane which produces a thick clear fluid called synovial fluid. This fluid lubricates and nourishes the cartilage and bones inside the joint capsule.
Within the knee joint between the femur and tibia, there are two C shaped cartilaginous structures called menisci. Menisci function to provide stability to the knee by spreading the weight of the upper body across the whole surface of the tibial plateau. The menisci help in load bearing by preventing the weight from concentrating onto a small area, which could damage the articular cartilage. The menisci also act as a cushion between the femur and tibia by absorbing the shock produced by activities such as walking, running and jumping.
Ligaments are tough bands of tissue that connect one bone to another bone. The ligaments of the knee function to stabilize the knee joint. There are two important groups of ligaments that hold the bones of the knee joint together, Collateral ligaments and the cruciate ligament.
Collateral ligaments are present on either side of the knee. They function to prevent the knee from moving too far during side to side motion. The collateral ligament on the inside is called the medial collateral ligament (MCL) and the collateral ligament on the outside is called the lateral collateral ligament (LCL).
Cruciate ligaments - This group of ligaments, present inside the knee joint, control the back and forth motion of the knee. The Cruciate ligament in the front of the knee is called anterior cruciate ligament or ACL and the cruciate ligament in the back of the knee is called posterior cruciate ligament or PCL.
Muscles: There are two major muscles, the quadriceps and the hamstrings, which enable movement of the knee joint. The quadriceps muscles are in the front of the thigh. When the quadriceps muscles contract, the knee straightens. The hamstrings are in the back of the thigh. When the hamstring muscles contract, the knee bends.
Tendons are structures that attach muscles to the bone. The quadriceps muscles of the knee meet just above the patella and attach to it through a tendon called the quadriceps tendon. The patella further attaches to the tibia through a tendon called the patella tendon. The quadriceps muscle, quadriceps tendon and patellar tendon all work together to straighten the knee. Similarly, the hamstring muscles at the back of the leg are attached to the knee joint with the hamstring tendon.
The anterior cruciate ligament, or ACL, is one of the major ligaments of the knee that is in the middle of the knee and runs from the femur (thigh bone) to the tibia (shin bone). It prevents the tibia from sliding out in front of the femur. Together with posterior cruciate ligament (PCL), it provides rotational stability to the knee.
Meniscus tears are the commonest knee injuries in athletes, especially those involved in contact sports. A sudden bend or twist in your knee can the meniscus to tear. This is a traumatic meniscus tear. Elderly people are more prone to degenerative meniscal tears as the cartilage wears out and weakens with age.
Arthritis is a general term covering numerous conditions where the joint surface or cartilage wears out. The joint surface is covered by a smooth articular surface that allows pain-free movement in the joint. This surface can wear out for several reasons; often the definite cause is not known.
The patella (knee cap) is a protective bone attached to the quadriceps muscles of the thigh by quadriceps tendon. The patella attaches with the femur bone and forms a patellofemoral joint. The patella is protected by a ligament which secures the knee cap from gliding out and is called a medial patellofemoral ligament (MPFL).
Loose bodies are small loose fragments of cartilage or a bone that float around the knee joint. The loose bodies can cause pain, swelling, and locking, and catching of the joint.
High tibial osteotomy is a surgical procedure performed to relieve pressure on the damaged site of an arthritic knee joint. It is usually performed in arthritic conditions affecting only one side of your knee and the aim is to take pressure off the damaged area and shift it to the other side of your knee with healthy cartilage.
Unicompartmental knee replacement is a minimally invasive surgery in which only the damaged compartment of the knee is replaced with an implant. It is also called a partial knee replacement.
Total knee replacement, also called total knee arthroplasty, is a surgical procedure in which the worn out or damaged surfaces of the knee joint is removed and replaced with artificial parts. The knee is made up of the femur (thigh bone), the tibia (shin bone), and patella (kneecap).
Medial patellofemoral ligament reconstruction is a surgical procedure indicated in patients with severe patellar instability. The medial patellofemoral ligament is a band of tissue that extends from the femoral medial epicondyle to the superior aspect of the patella.
The anterior cruciate ligament (ACL) is one of the major stabilizing ligaments in the knee. It is a strong rope like structure located in the centre of the knee running from the femur to the tibia. When this ligament tears, unfortunately, it does not heal and often leads to the feeling of instability in the knee.