Articular cartilage lesions is a term used to describe injuries where the articular cartilage of the knee joint is affected. Lesions often show up as tears or potholes in the surface of the cartilage. Cartilage problems are relatively common and can develop by injury or normal wear and tear. Articular cartilage does not have a blood supply of its own. Because of that, it does not have the natural ability to heal itself when damaged.
What is Knee Cartilage?
Articular cartilage covers the ends of bones. It has a smooth, slippery surface, which allows the bones of the knee joint to slide over each other without rubbing. This slick surface is designed to minimize pressure and friction as you move.
Surgeons classify defects in knee cartilage using a grading scale from I (one) to IV (four).
- Grade I lesions mean the cartilage has a soft spot
- Grade II lesions show minor tears in the surface of the cartilage
- Grade III lesions have deep crevices
- Grade IV lesions mean the tear goes all the way to the underlying bone
Grade IV lesions are diagnosed as a full-thickness lesion. Sometimes, part of the torn cartilage will break off inside the joint. The more it moves around freely within the joint, the more damage it causes to the surface of the cartilage. This unattached piece is sometimes called a loose body.
Cartilage lacks a supply of blood or lymph vessels, which normally nourish other parts of the body. Without a direct supply of nourishment, cartilage is not able to heal itself when damaged. If the cartilage is torn all the way down to the bone, however, the blood supply from inside the bone is sometimes enough to start some healing inside the lesion.
In cases like this, the body will form a scar in the area using a special type of cartilage called fibrocartilage. Fibrocartilage is a tough, dense, fibrous material that helps fill in the torn part of the cartilage. Yet it's not an ideal replacement for the smooth, glassy articular cartilage that normally covers the surface of the knee joint.
To learn more about the anatomy of the knee, download our educational document A Patient’s Guide to Knee Anatomy.
Symptoms of Knee Cartilage Injuries
Initially, because cartilage tissues are not supplied with nerves, injuries often go unnoticed because there is no pain. In fact, surgeons often discover lesions in the knee joint cartilage while doing knee surgery for a completely different problem.
Sometimes, however, holes or rough spots in the cartilage can throw off the intricate design of the knee joint. If this happens, the joint can become inflamed and painful.
If the lesion is large enough, the bone below the cartilage loses protection. This leaves the bone vulnerable to pressure and strain, which can eventually become a source of pain. If the cartilage injury goes untreated, it may eventually cause other problems in the joint.
It is important to understand that lack of pain does not mean the lesion is not causing problems. As mentioned earlier, articular cartilage lesions do not heal by themselves. And they often get worse over time, not better. This is why surgery is often the recommended treatment for this condition. Your orthopedic surgeon will take images of the knee to understand the severity of the lesions and from there will discuss with you whether knee joint surgery is necessary.
You can learn more about articular cartilage injuries by downloading our educational document A Patient’s Guide to Articular Cartilage Problems of the Knee.