Injuries to the articular cartilage in the knee joint are common. These injuries, called lesions, often show up as tears or “pot holes” in the surface of the cartilage. If a tear goes all the way through the cartilage, doctors call it a full-thickness lesion. When this happens, surgery is usually recommended.
Articular cartilage covers the ends of bones. It has a smooth, slippery surface allowing 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.
Cartilage tissues are not supplied with nerves. However, holes or rough spots in the cartilage can cause the joint to become inflamed and painful. If the injury, or lesion, is large enough, the bone below the cartilage loses protection. Pressure and strain on this unprotected portion of the bone can also become a source of pain.
Doctors classify damage to knee cartilage using a grading scale from one to four.
Grade One – the cartilage has a soft spot.
Grade Two – minor tears visible in the surface of the cartilage.
Grade Three – lesions have deep crevices.
Grade Four – the cartilage tear exposes the underlying bone.
A grade four lesion goes completely through all layers of the cartilage. Sometimes part of the torn cartilage will break off inside the joint. Since it is no longer attached to the bone, it can move around within the joint, causing more damage to the surface of the cartilage. Some doctors refer to this as 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 if it gets injured. If the cartilage is torn all the way to the bone, the blood supply inside the bone is sometimes enough to start some healing inside the lesion. In cases like this, the body will form a scar, called a full-thickness lesion, in the area with 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 articular cartilage that normally covers the surface of the knee joint.
Articular cartilage lesions do not always cause symptoms. Just because there is no pain does not mean the lesion is not causing problems. In general, partially torn lesions do not heal by themselves, and they often get worse over time.
Full-thickness lesions may not cause any symptoms at first. The fibrocartilage that fills in the injured space often doesn’t match the shape of the joint surface. The body may have problems adapting to the altered shape of the joint, which can eventually even change the way the joint works.
When the lesion causes pain, surgery will most likely be recommended. If the lesion is not causing symptoms, surgeons will weigh many factors before recommending surgery, such as the patient’s age, lifestyle, and the overall condition of the knee.
Even if patients have pain, they may not have surgery right away. Doctors may start by recommending ways to manage the symptoms. This could be as simple as applying heat or ice and taking prescription medication. Often, doctors will recommend patients work with a physical therapist. A knee brace or shoe orthotic may be issued to improve knee alignment to ease pressure on the sore knee.
Many types of surgery have been developed for fixing articular cartilage injuries in the knee. When the decision is made to go ahead with surgery, the doctor will consider whether to do a procedure to restore or to repair the cartilage. A reparative surgery helps fill in the lesion, but doesn’t restore the actual makeup and function of the articular cartilage.
Restorative surgery fills the lesion to the full depth with tissue almost identical to the original. One surgical method is to transplant cartilage and underlying bone from a nearby area in the knee joint. Another method is to take some primary cartilage cells (chondrocytes) from the knee, grow them in a laboratory, and then use the newly grown tissue to fill in the lesion at a later date.
Your doctor will decide which surgery to use based on your specific injury, age, activity level, and the overall condition of your knee.
Doctors use an arthroscope and small, specially designed instruments to see into the joint and trim the rough edges of cartilage and remove loose fragments. Arthroscopic debridement is referred to as chondroplasty. It is only intended to be a short-term solution, but it is often successful in relieving symptoms for a few years. This procedure is usually used when the lesion is too large for a grafting type procedure or the patient is older and an artificial knee is planned for the future.
If the joint has become arthritic, the tissue within and below the lesion can become hard. During arthroscopy the surgeon can use a special instrument known as a burr to perform an abrasion arthroplasty. In this procedure, the surgeon carefully scrapes off the hard bone tissue from the surface of the lesion. The scraping action instigates a healing response in the bone. In time, new blood vessels enter the area and fill it with new fibrocartilage.
Doctors use a blunt instrument (awl) to poke a few tiny holes in the bone under the cartilage. This procedure is used to get the bone layer under the cartilage to produce a healing response. The fresh blood supply starts the healing response and triggers the body to start forming fibrocartilage inside the lesion.
Autologous Chondrocyte Implantation
Doctors may recommend this procedure for active, younger patients (twenty to fifty years old), when the bone under the lesion hasn’t been badly damaged, and when the size of the lesion is small (less than four centimeters in diameter). The doctor surgically removes a few chondrocytes from inside the knee cartilage. These cells are grown in a laboratory. At a later date, the patient returns for a second surgery, during which the doctor implants the newly grown cartilage into the lesion and covers it with a small flap of tissue. The cover holds the cells in place while they attach themselves to the surrounding cartilage and begin to heal.
An autograft is a procedure for grafting tissue from the patient’s own body. The place where the graft is taken is called the donor site. In this case, doctors graft a small amount of bone (osteo) and cartilage (chondral) from the donor site to put into the lesion. Usually, the donor site for this procedure is on the joint surface of the injured knee. Doctors are careful to take the graft from a spot that won’t cause a lot of problems, usually on the top and outside border of the knee cartilage. The osteochondral autograft procedure has mostly been used to treat osteochondritis dissecans (OCD), a condition where a chunk of the cartilage and the layer of bone beneath have died.
During this procedure, doctors graft tissue from another person. The osteochondral allograft procedure is mostly used after other surgeries have failed. It is not recommended for patients with osteoarthritis. One of the problems with this kind of procedure is the limited supply of donor tissue. This procedure usually involves placing rather large pieces of cartilage and bone in the joint. The allograft is usually held in place with metal screws or pins.
As with all major surgical procedures, complications can occur. This is not intended to be a complete list of complications, but these are some of the most common: anesthesia complications, infection, failure of implanted metal screws or pins, failure of surgery.
Since surgeons use different methods when treating articular cartilage lesions in the knee, the instructions patients need to follow after surgery depend on the doctor and the way the surgery was done.
Depending on the type of surgery, some doctors have their patients use a continuous passive motion (CPM) machine to help the knee begin to move and to alleviate joint stiffness. This machine is used on many different types of surgery involving joints and is usually started immediately after surgery. The machine simply straps to the leg and continuously bends and straightens the joint. This motion has been shown to reduce stiffness and pain, and help the joint surface heal better with less scarring.
Many doctors will have their patients take part in physical therapy after knee surgery for articular cartilage injuries. The first few physical therapy treatments are designed to help control the pain and swelling from the surgery. Physical therapists will also work with patients to make sure they are only putting a safe amount of weight on the affected leg.
With the exception of those who underwent the debridement method, patients will be instructed to avoid putting too much weight on their foot when standing or walking for up to six weeks. This gives the area time to heal. People treated with an allograft are often restricted in their weight bearing for up to four months.
Patients are strongly advised to follow the recommendations about how much weight is safe. They may require a walker or pair of crutches for up to six weeks to avoid putting too much pressure on the joint when they are up and about.
The physical therapist will choose exercises to help improve knee motion and to get the muscles toned and active again. At first, emphasis is placed on exercising the knee in positions and movements that don’t strain the healing part of the cartilage. As the program evolves, more challenging exercises are chosen to safely advance the knee’s strength and function.
Ideally, patients will be able to resume their previous lifestyle activities. Some patients may be encouraged to modify their activity choices, especially if an allograft procedure was used.