Knee cartilage injury

Inside a joint, the bone ends are capped with articular cartilage, a smooth, slick layer that lets the surfaces slide against each other almost without friction. A cartilage injury is a damaged area of this surface, sometimes involving the bone underneath, caused by a twisting injury, a blow, a kneecap dislocation, or a condition called osteochondritis dissecans. Cartilage has no blood supply, so it has very limited ability to heal on its own.

• Knee pain with activity, standing, or stairs
• Swelling after activity
• Catching, grinding, or clicking
• Locking, if a loose piece of cartilage or bone moves inside the joint
• Stiffness

Some small areas of damage cause no symptoms and are found by chance.

• Sudden injuries, such as a twisting fall, an ACL tear, a kneecap dislocation, or a direct blow
• Osteochondritis dissecans (OCD), in which a small segment of bone beneath the cartilage loses its blood supply and can soften or come loose; it is seen most often in active children and teens
• Problems that overload one area of the knee, such as poor leg alignment, ongoing instability, or loss of a meniscus

Widespread, gradual loss of cartilage across the joint is osteoarthritis, which is treated differently from a single, limited area of damage.

X-rays do not show cartilage itself, but they show the bone, many OCD lesions, leg alignment, and signs of arthritis. An MRI gives a much better view of the cartilage and the bone beneath it. Sometimes the full extent of the damage is seen only during arthroscopy.

Non-surgical care includes changing or reducing the activities that cause pain, physical therapy to strengthen the muscles that support the knee, weight management when appropriate, anti-inflammatory medication when appropriate, and sometimes an injection. For OCD in children and teens whose growth plates are still open and whose lesion is stable, a period of activity restriction, sometimes with a brace or crutches, may allow it to heal.

When surgery is needed, the approach depends on the size, depth, and location of the damage, the patient's age and activity, and other problems in the knee. Options include:

• Arthroscopic debridement: smoothing loose edges and removing loose pieces
• Fixation: reattaching a loose fragment of cartilage and bone, common with OCD
• Marrow stimulation (microfracture): making small holes in the bone beneath a small defect so that repair tissue can form
• Osteochondral grafting: filling the defect with plugs of cartilage and bone, either from a less-used part of the same knee or from a donor
• Cell-based cartilage implantation: growing the patient's own cartilage cells in a lab and implanting them in a second operation

Malalignment, instability, or a missing meniscus may be corrected at the same time. Cartilage restoration techniques are still evolving, and they are generally aimed at younger patients with a limited area of damage rather than widespread arthritis.

Cartilage procedures usually require a period of protected weight bearing and a long, gradual rehabilitation, because new repair tissue takes time to mature. The return to running and impact sports is staged over many months and depends on the procedure performed.

Getting knee injuries such as ACL tears and kneecap dislocations evaluated and treated, keeping the leg muscles strong, and addressing a knee that keeps giving way can help protect the joint surface.