Anterior Cruciate Ligament
In Depth: Connective Tissue 02
Inside the knee joint capsule, a connective tissue that encases the knee, there are several important ligaments and structures that protect the knee and keep its movement as smooth as possible.
Inside this capsule are pads that cushion the joint. One of those pads is a bursa, a sac filled with a slimy liquid that helps prevent friction between bones in the joint. There is also a fat deposit known as the infrapatellar fat pad that cushions the space below the knee cap and the heads of the femur and tibia.
Also between the heads of the femur and tibia are the menisci. These are the medial meniscus and lateral meniscus. These horseshoe-shaped pads of cartilage 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 when bent — and degeneration, 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 together and protect the knee from twisting, impact, and other potentially harmful movements.
There are four major ligaments of the knee. Two are located inside the knee joint capsule. They are:
- Anterior cruciate ligament (ACL): The cruciate ligaments form a cross in the middle of the knee inside the knee joint capsule. The ACL stretches from the front of the head of the tibia to the back of the head of the femur to prevent the tibia from moving forward. Injury to the ACL is common in twisting movements, such as freestyle rollerblading. A torn ACL often requires reconstructive surgery and extensive physical rehabilitation.
- Posterior cruciate ligament (PCL): This ligament wraps around the ACL as it travels from the back of the head of the tibia to the back of the head of the femur. It is most commonly injured by direct impact when the knee is flexed, such as striking a dashboard in a car accident.