Cartilage defects in the knee involve damage to the articular cartilage, which is the smooth substance that covers the ends of the bones and keeps them from rubbing together during movement. Cartilage damage is known as a lesion and can range from a soft spot on the cartilage (Grade I lesion) or a small tear in the top layer to an extensive tear that extends all the way to the bone (Grade IV or full-thickness lesion). Sometimes a piece of cartilage breaks off and causes more damage to the cartilage and bone as it is ground in the joint.
When cartilage defects are present, they are distinct from meniscal tears, which also occur in the cartilage of the knee. However, the meniscus is a different type of cartilage than the articular cartilage that is found on the ends of the femur and tibia. When a cartilage defect is present, there may be a hole in or damage to the articular cartilage that produces pain and a catching or grinding sensation in the knee.
Cartilage defects may be degenerative, resulting from wear and tear over time, or traumatic, typically caused by an injury such as falling on the knee, jumping down or rapidly changing direction while playing a sport. They do not always produce symptoms at first because there are no nerves in the cartilage. Over time, however, defects can disrupt normal joint function and lead to pain, inflammation, and limited mobility. The defect may gradually worsen or cause other problems in the joint.
Cartilage also lacks blood supply, so the body cannot usually repair defects on its own. However, some severe tears that injure the bone can promote the growth of scar tissue known as fibrocartilage, a tough material that replaces the missing articular cartilage but does not provide as smooth a gliding surface.
In order to diagnose a defect in the cartilage of the knee, a doctor will take a medical history and perform an examination. Imaging tests provide views of the tissue and bone within the knee to help the doctor evaluate the cause of the knee pain. The imaging tests performed may include radiographs and MRI scans.
Cartilage defects range widely in their size and the degree of damage they may cause. They need to be thoroughly assessed based on a number of factors including their location and the age and activity level of the patient before a treatment plan can be determined. For some patients, conservative treatment methods such as resting the knee, wearing a brace, taking non-steroidal anti-inflammatory medications and injections of corticosteroids may be used if the defects produce only mild symptoms. However, in most cases, a surgical treatment will be necessary to provide relief from pain and other symptoms.
Older patients who have smaller cartilage defects with mild symptoms may be suitable candidates for debridement. This arthroscopic procedure involves several small incisions in the knee into which a tiny camera and instruments are inserted. The loose or damaged tissue will be removed, but the defects are typically not repaired.
Microfracture is an arthroscopic procedure performed to repair damaged knee cartilage, often used on athletes who may have suffered cartilage injuries while playing sports. During the microfracture procedure, a small surgical tool called an awl is inserted into the knee to create small holes, known as microfractures, in the bone near the defects to help release the cells that produce cartilage and restore the damaged area. The number of holes created varies depending on the size and location of the area being treated, with most patients requiring five to 15 small holes.
This procedure takes healthy cartilage from another area of the bone that does not bear weight and transplants it to the damaged, weight-bearing area. This is used for smaller defects and involves filling holes with small quantities of transplant materials. One of these methods is mosaicplasty, which is a transferring of cartilage from a healthy part of a joint to the area that has experienced damage.
This procedure takes a sample of healthy cartilage and multiplies it in large quantities outside the body before being implanted back onto the bone. This newly grown cartilage coats the bone and provides regained support.