The knee is a meeting place for four bones — the femur (thigh bone), tibia (shinbone), fibula (calf bone), and patella (kneecap). It requires several ligaments to keep these bones in place and maintain its ability to flex and bend.
The knee joint capsule, also known as the articular capsule of the knee, is an important structural component. Like many other joints in the body, the knee has a dense, fibrous, connective tissue that seals the joint space between the bones. In the knee, these bones are the femur and tibia. The patella sits outside the capsule.
Inside this capsule are pads that cushion the joint. One of those pads isa bursa, a sac filled with a gelatinous liquid that helps prevent friction between bones in the joint. When the fluid becomes irritated or infected, it is known as bursitis, a condition that can make joint movement painful and stiff in the morning.
Also between the heads of the femur and tibia are the menisci. These are the medial meniscus and lateral meniscus. These are horseshoe-shaped pads of cartilage, a kind of strong, flexible tissue. They lie opposite each other on the inner (medial) and outer (lateral) edges of the tibia. They act as shock absorbers in the knee and help with weight distribution among the bones.
The menisci are prone to injury from trauma — most commonly in athletes when the knee is twisted while in a flexed position— and degeneration (arthritis), such as in older people. Damage to this cartilage often creates pain and tenderness in the joint along with clicking in the joint. Severe damage often requires surgery.
Ligaments are tough bands of fibrous tissue that connect bones. In the knee and other joints, they absorb pressure from twisting, impact, and other potentially harmful movements to ensure the bones stay in place.
There are four major ligaments of the knee. Two are located outside the knee joint capsule. They are:
The two ligaments that are located inside the knee joint capsule are the cruciate ligaments. They form a cross in the middle of the knee, inside the knee joint capsule. These ligaments are: