A guide to the principal structures of the knee joint and the mechanical functions they perform.
The longest and strongest bone in the body, the femur forms the upper portion of the knee joint. Its rounded medial and lateral condyles articulate with the tibia below, distributing the compressive forces of the body's weight through the joint.
The larger of the two lower leg bones, the tibia bears the majority of weight transmitted through the knee. Its broad, flat upper surface — the tibial plateau — receives the femoral condyles and provides the foundation of the joint.
The largest sesamoid bone in the body, the patella sits within the quadriceps tendon at the front of the knee. It acts as a mechanical pulley, increasing the leverage of the quadriceps muscle and protecting the underlying joint from direct impact.
Running alongside the tibia, the slender fibula bears little body weight but provides an important attachment site for the lateral collateral ligament and the muscles of the lower leg. Its head is palpable just below the outer knee.
One of the two cruciate ligaments crossing inside the joint, the ACL prevents the tibia from sliding forward relative to the femur and controls rotational stability. It is one of the most commonly injured structures in sport, particularly in pivoting and landing movements.
The stronger of the two cruciate ligaments, the PCL resists posterior displacement of the tibia on the femur. It is vital for stability during downhill walking, squatting, and resisting direct blows to the front of the shin.
Running along the inner surface of the knee, the MCL connects the femur to the tibia and resists forces that push the knee inward (valgus stress). It is the primary restraint against excessive side-to-side movement on the medial side.
On the outer aspect of the knee, the LCL connects the femur to the fibula and resists varus forces — those that push the knee outward. It works in concert with surrounding structures to maintain lateral joint integrity.
A C-shaped wedge of fibrocartilage on the inner compartment of the knee. It deepens the tibial surface, absorbs shock, distributes load, and aids joint lubrication. It is less mobile than its lateral counterpart and therefore more susceptible to tears.
More circular and mobile than the medial meniscus, the lateral meniscus covers a greater proportion of the lateral tibial plateau. It performs the same shock-absorbing and load-distributing role on the outer compartment of the knee.
A layer of smooth hyaline cartilage covering the ends of the femur, tibia, and the underside of the patella. It provides an almost frictionless surface for joint movement and absorbs compressive forces, but has very limited capacity for self-repair once damaged.
Connecting the lower pole of the patella to the tibial tuberosity, the patellar tendon is the final link in the extensor mechanism of the knee. Contraction of the quadriceps is transmitted through this tendon to straighten the leg.
The combined tendon of the four quadriceps muscles, inserting into the upper pole of the patella. It is the most powerful tendon crossing the knee and is critical for walking, running, climbing, and rising from a seated position.
The broad, flat upper surface of the tibia that articulates with the femoral condyles. Divided into medial and lateral compartments, it serves as the platform through which the entire weight of the body is transmitted to the lower leg.
Human Orthopaedic Anatomy — Educational Reference — 2026