What Are the Parts of the Knee?

What Are the Parts of the Knee?
Like any joint, the knee is composed of bones and cartilage,
ligaments, tendons, and muscles.
Bones and cartilage
The knee joint is the junction of three bones: the femur
(thigh bone or upper leg bone), the tibia (shin bone or
larger bone of the lower leg), and the patella (knee cap).
The patella is 2 to 3 inches wide and 3 to 4 inches long.
It sits over the other bones at the front of the knee joint
and slides when the knee moves. It protects the knee and
gives leverage to muscles.
The ends of the three bones in the knee joint are covered
with articular cartilage, a tough, elastic material that helps
absorb shock and allows the knee joint to move smoothly.
Separating the bones of the knee are pads of connective
tissue called menisci (men-NISS-sky). The menisci are
two crescent-shaped discs (each called a meniscus
(men-NISS-kus) positioned between the tibia and femur
on the outer and inner sides of each knee. The two menisci
in each knee act as shock absorbers, cushioning the lower
part of the leg from the weight of the rest of the body as
well as enhancing stability.
Muscles
There are two groups of muscles at the knee. The four
quadriceps muscles on the front of the thigh work to
straighten the knee from a bent position. The hamstring
muscles, which run along the back of the thigh from the
hip to just below the knee, help to bend the knee.

Tendons and ligaments
The quadriceps tendon connects the quadriceps muscle to
the patella and provides the power to straighten the knee.
The following four ligaments connect the femur and tibia
and give the joint strength and stability:
• The medial collateral ligament (MCL), which runs
along the inside of the knee joint, provides stability
to the inner (medial) part of the knee.
• The lateral collateral ligament (LCL), which runs
along the outside of the knee joint, provides stability
to the outer (lateral) part of the knee.
• The anterior cruciate ligament (ACL), in the center
of the knee, limits rotation and the forward movement
of the tibia.
• The posterior cruciate ligament (PCL), also in the
center of the knee, limits backward movement of
the tibia.
The knee capsule is a protective, fiber-like structure that
wraps around the knee joint. Inside the capsule, the joint is
lined with a thin, soft tissue called synovium.