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September 2010: Articular Cartilage Injuries of the Knee

31 Aug 2010

Dr. Gabriel S. Levi is a fellowship-trained orthopedic surgeon at Weiss Memorial Hospital. He completed his fellowship training in joint reconstruction at the world-renowned Insall Scott Kelly Institute in New York City. His specialties include joint reconstruction and sports medicine. Dr. Levi has a special interest in cartilage injuries and joint replacement of the knee and hip. He is also bilingual in Spanish and English.

Gabriel Levi, M.D.
Orthopedic Surgeon
Orthopaedic and Rehabilitation Centers
Weiss Memorial Hospital
(773) 878-6233

There are two very important types of cartilage in the knee: articular cartilage and meniscus cartilage. Articular cartilage covers the ends of the bones that make up the knee joint. Meniscus cartilage acts as a shock absorber between the bones. Read about meniscus cartilage here.

Articular Cartilage
Articular cartilage is very smooth and slippery and allows for fluid movement of the knee. It is the same structure with which we are all familiar, the white shiny surface on the end of a chicken or turkey bone. When this cartilage is healthy and intact, it allows for normal, pain-free motion of the knee. However, an injury to the cartilage can be painful and can lead to progressive limitation in function. Fortunately, there are many treatment options for these injuries.

Articular cartilage injuries in the knee are common and can occur several ways. Often the culprit is a twisting injury or traumatic impact to the knee. At times the articular cartilage can be injured without any known cause as in the common conditions of osteochondritis dessicans and avascular necrosis (AVN). In both of these conditions, the bone beneath the articular cartilage is unhealthy, and often a fragment of the bone and cartilage may separate from the remaining healthy bone and cartilage. This is referred to as an osteochondral fragment or defect (OCD), resulting in a "loose body" of cartilage and bone floating around the knee. A "loose body" may cause additional pain, functional limitation and further damage to the otherwise healthy surrounding cartilage. When there is a defect in the articular cartilage, the contour of the joint is no longer smooth, and pain, stiffness and further cartilage damage may result.

Degenerative changes can occur in the articular cartilage at any age, but usually occur over time and represent "wear and tear." As the degeneration worsens, the knee becomes arthritic, as in the common condition of osteoarthritis or degenerative joint disease. Initially the cartilage becomes soft compared to the healthy articular cartilage. In this stage there does not appear to be any visible tear of the cartilage and all of the damage occurs on a microscopic level. These injuries progress from surface "fraying" to fissuring or "cracking" of the cartilage and eventual separation of the cartilage from the underlying bone. 

Diagnosis
The first step in diagnosis of an articular cartilage injury is a good history and physical examination by a physician well-trained in diagnosis and treatment of knee injuries. X-ray images of the knee are necessary to help determine a diagnosis. After these initial steps, a Magnetic Resonance Image (MRI) is often helpful in reaching a diagnosis. Some times both the X-ray and MRI do not show an articular cartilage lesion, but one is suspected by the history and the physical examination. In these cases, the best diagnostic study is a small surgical procedure called arthroscopy, which is described below. 

Treatment
To date, there are no medicines that can grow cartilage. Some dietary supplements are available over the counter; however, scientific studies have only been able to show that they may have a small, pain-reducing effect. They have never been shown to restore, replace, re-grow or heal articular cartilage injuries. 
 
Surgical Treatments
Because of the importance of articular cartilage to normal, painless function of the knee, innovative treatments have been developed which are aimed at joint restoration and preservation. The goal of treatment is to restore a smooth normal contour of the articular surface, which will ultimately lead to more normal and pain-free motion. When the articular cartilage injury is isolated and does not affect the entire joint, these techniques of joint restoration and preservation can be used. Which treatment is used depends on the size, shape and location of the injury, as well as the patient’s specific goals and expectations.

Arthroscopy
Many treatments can be performed through a minimally invasive surgery called arthroscopy. Arthroscopy is an outpatient surgery performed through small punctures in the skin that allows the surgeon to see the entire cartilage surface of the knee. The surgery is performed using a small camera and specialized instruments that are only a few millimeters wide. Patients are able to walk and go home on the same day of surgery. We do encourage patients to start physical therapy the day after surgery. Often we require a short period of time, up to six weeks, on crutches after this surgery in order to protect the site of treatment and allow it to have the best chance of growing new cartilage.

It is important to remember that once the articular cartilage injury is too severe, diffuse, or widespread throughout the joint, these techniques are no longer effective, and joint replacement becomes the only option for effective and long lasting treatment.

Microfracture
Microfracture, a controlled process of creating small holes in the bone that is exposed due to the articular cartilage injury, is another excellent technique. These small holes in the bone serve as channels for blood to flow into the site of injury and bring in cells which have the potential to grow new cartilage and fill in the defect left from the original injury.   While this new cartilage is not exactly the same as normal articular cartilage, it still provides good pain relief and allows the patient to regain more normal function about 80 percent of the time. This procedure is performed using arthroscopy as described above.

Osteochondral Autograft, Allograft or Synthetic Plugs
Another excellent technique used to treat isolated lesions of the articular cartilage is osteochondral autograft transfer (OAT) or osteochondral allograft transplantation. In the OAT technique, a plug of bone and cartilage is taken from a part of the knee that does not need the cartilage (donor site) and is transferred to the articular cartilage defect at the site of injury. This replaces the injured cartilage with the patient’s own natural cartilage.  In some situations a plug of bone and cartilage from a cadaver knee (osteochondral allograft transplantation) can be used, and this has very similar results. Both techniques are highly effective and have excellent results greater than 80 percent of the time.

An emerging technique is the use of synthetic cartilage scaffolds or plugs. These synthetic materials are manufactured to mimic bone and cartilage and serve as a structure in which the body’s own bone and cartilage cells can grow. In the long run, the body lays down new bone and cartilage and ultimately fills in the defect. The benefit to the use of the scaffolds is that the surgery can be performed in a more minimally invasive manner through all arthroscopic technique and usually does not require an open incision around the knee. Rehabilitation is significantly shorter and people tend to return to their normal activities much more quickly than with the other described techniques.

Cartilage Cell Implantation or Transplantation
Several new techniques have been developed in an attempt to grow normal articular cartilage and one technique has begun to show good results. Autologous cartilage implantation (ACI) is a surgery in which a patient’s own cartilage is biopsied, grown in a laboratory and then implanted into the defect at the site of injury. The implanted cells have been shown to reliably fill in the defect with new cartilage. This technique has the longest track record of all cartilage implantation techniques and is thought to significantly reduce pain and improve function about 80 percent of the time.

Lastly, the new technique of cartilage cell transplantation involves transplantation of donated young cadaver cartilage cells specially prepared by the manufacturers. These cartilage cells have the potential to grow and replace cartilage defects at the site of injury.  One advantage of this technique is that it can be performed with a single surgery and without the process of growing the cells in a laboratory. Both of the cartilage cell implantation or transplantation techniques described are usually performed through an open approach to the knee and are not arthroscopic surgeries. 

Summary
Articular cartilage injuries of the knee are very common. Isolated lesions can be treated with selective techniques depending on the size, location and severity of the injury. Many of these techniques can be performed using minimally invasive arthroscopy. The goal of treatment is to restore a smooth normal contour of the articular surface, which will ultimately lead to more normal and pain-free motion. Early treatment of these injuries is important to help prevent further degeneration of the cartilage, which eventually leads to severe arthritis of the knee.

For more information
If you would like more information about knee injuries and or would like an appointment please call Dr. Levi’s office at the Orthopaedic and Rehabilitation Centers, (773) 878-6233.