Knee Anatomy
Understanding the anatomy of the knee is essential for diagnosing and treating injuries and conditions affecting this joint.
The knee is a complex joint that connects the thigh to the shin. The knee joint allows for various movements such as flexion (bending), extension (straightening), and slight rotation. The knee joint is composed of several structures:
Bones
Femur: The thigh bone, which forms the top part of the knee joint.
Tibia: The shin bone, which forms the bottom part of the knee joint.
Patella: The kneecap, a small bone located in front of the knee joint. It protects the knee and provides leverage for the thigh muscles (quadriceps). The patella moves on the front part of the femur in a groove called the “trochlea groove”.
Muscles
Muscles are structures that move the joint. For a muscle to move a joint it must cross the respective joint.
The knee muscles form three major groups:
Quadriceps Muscles: A group of four muscles located at the front of the thigh which work together to extend the knee.Hamstring Muscles: Located at the back of the thigh, these muscles help flex the knee.Gastrocnemius and Soleus: Calf muscles that cross the knee joint and assist in knee flexion.
Tendons
Quadriceps Tendon: Connects the quadriceps muscles to the patella.
Tendons are thick tissue structures that connect muscles to bone.
Patellar Tendon: Connects the patella to the tibia. It is also called the patellar ligament as it connects two bones.
Cartilage
The knee joint, like any other joint in the body is covered by articular cartilage.
Articular Cartilage: Covers the ends of the femur, tibia, and back of the patella. It provides a smooth, gliding surface for the bones to move against each other, reducing friction and allowing for seamless movement. Wear of this articular cartilage is defined as arthritis.
In addition to articular cartilage, the knee joint contains two structures called menisci.
Meniscus: Two C-shaped wedges of cartilage on the inner (medial meniscus) and outer part (lateral meniscus) of the joint, located between the femur and tibia. They are similar to the articular cartilage but are more rubbery in consistency. They act as shock absorbers, distribute weight, and enhance stability in the knee joint. Their primary function is to protect the articular cartilage from wear and tear.
Ligaments
Ligaments are tissue structures that connect one bone to another. Their main function is to provide stability to a joint. There are four main ligaments in the knee joint that run between the femur and the tibia.
Anterior Cruciate Ligament (ACL): Located in the center of the knee, it prevents the tibia from sliding too far forward and provides rotational stability
Posterior Cruciate Ligament (PCL): Also located in the center of the knee, it prevents the tibia from sliding too far backward.
Medial Collateral Ligament (MCL): Runs along the inner side of the knee, providing stability and preventing excessive inward movement (valgus stress).
Lateral Collateral Ligament (LCL): Runs along the outer side of the knee, providing stability and preventing excessive outward movement (varus stress).
The anterolateral ligament (ALL) runs along the outside of the knee and is ofen injured at the same time as the ACL.
Medial Patellofemoral Ligament (MPFL) is an additional ligament that runs between the inner part of the femur to the inner border of the patella. It provides stability to the patella in its movement at the front of the knee.
In a total knee replacement, the entire knee joint surface is replaced – the ends of the femur (thigh bone), tibia (shin bone), and usually the underside of the kneecap are all resurfaced with artificial components. In a partial knee replacement (PKR), also called unicompartmental knee replacement, only the damaged compartment of the knee is replaced, leaving healthy bone, cartilage, and ligaments intact.
Diagnosis involves understanding a history of your symptoms, examining your knee, and using imaging such as X-rays to assess cartilage wear and joint alignment. In some cases, additional scans such as CT or MRI scans may be required to either exclude other conditions or quantify the degree of arthritis.Some patients develop patellofemoral pain syndrome in the absence of any bone, joint or soft tissue abnormalities. However, most patients with the syndrome present with one or more abnormalities related to bone anatomy, joint anatomy and/or soft tissue.
Although knee arthritis can affect anyone, there are several factors that can increase the risk of arthritis:
- Genetic predisposition
- Previous knee injury or surgery
- Other joint conditions such as rheumatoid arthritis or gout
- Occupations involving heavy manual work
- Age (over 40)
- Female gender
- Being overweight or obese
- Participation in high impact activities or sports (e.g. running, soccer or rugby)
Knee arthritis typically develops as a result of progressive cartilage wear within the joint. This process may occur naturally with age or be accelerated by factors such as previous injury, altered joint alignment, or increased mechanical load.
In some cases, inflammatory conditions such as rheumatoid arthritis can also contribute to joint degeneration.
