Anatomy of a Knee Joint

Bones Overview

The knee connects the upper leg bone to the lower leg bone. Cartilage covers the ends of both leg bones and the underside of the patella, or knee cap. When these surfaces are smooth, the joint glides easily and without pain.

Femur

The femur, also known as the thigh bone, is the longest, largest and heaviest bone of the body. It is located above the knee.

Condyle

The condyle makes up the rounded end of the femur. This smooth surface allows the femur to move easily over the tibia's meniscus.

Patella

The patella, or knee cap, is a bone that is connected to the patella ligament, below, and the quadriceps tendon, above. The underside of the patella has a smooth surface and glides over the knee joint when the leg is extended or bent.

Tibia

The tibia is the lower leg bone. Also called the shin bone, it is the second longest bone of the body, and is located below the knee.

Meniscus

The medial meniscus and the lateral meniscus act like cushions and distribute the weight of the femur.

Fibula

The fibula is the thin bone located on the outside of the tibia.

Soft tissue overview

The soft tissues of the knee include many ligaments and tendons designed to hold the joint together and provide stability.

Quadriceps tendon

This tendon connects the patella to the quadriceps femoral muscle above it. The muscle and tendon pull the patella over the front of the knee joint to extend the lower leg.

Patella tendon

The patella tendon helps secure the patella over the front of the knee joint.

Collateral ligaments

The lateral and medial collateral ligaments minimize side to side movement and help stabilize the knee.

Anterior cruciate ligament

The anterior cruciate ligament (ACL) connects the front of the tibia to the back of the femur. It keeps the tibia from sliding forward and limits its rotation.

Posterior cruciate ligament

The posterior cruciate ligament (PCL) keeps the tibia from sliding backward.