The knee joint is made up of three bones – the thigh bone (femur), the shin bone (tibia), and the kneecap (patella). The ends of the bones are covered by a hard, white, Teflon-like tissue known as the “articular cartilage” that helps the bones glide smoothly with joint motion. When the articular cartilage wears down with age, this is called osteoarthritis. The articular cartilage may also be damaged during a twisting or pivoting injury, or by a direct impact to the knee. These injuries are known as chondral injuries.
Common mechanisms of injury include falls, sports injuries, or motor vehicle accidents. Injuries to the articular cartilage may also occur in association with knee ligament injuries, such as ACL tears or meniscus injuries. Small pieces of cartilage may occasionally break off and float around the knee as “loose bodies.” Occasionally, however, there is no clear history of a single injury. The condition may result from a series of minor injuries that have occurred over time.
Symptoms of articular cartilage injuries frequently involve pain, which is generally worse with activity. Depending on the location of the chondral injury in the knee, deep knee bending may make the pain worse. If the patella end of the femur is involved, pain may be worse when climbing stairs or squatting. Constant or intermittent swelling of the knee may occur in relation to certain activities. Finally, symptoms such as locking, catching, or painful popping may occur. In patients with loose bodies, they may experience irregular locking of the knee or the sensation of something loose that is moving around the knee.
Diagnosis of chondral injuries is made from a history of patient’s symptoms combined with findings from a physical examination. X-rays may be helpful in making the diagnosis, but are often normal. A MRI will usually detect the articular cartilage injury ; however, a definitive diagnosis of the size and extent of the chondral damage may only be determined at the time of surgery with direct visualization of the joint surface.
Treatment options for articular cartilage injuries depend on patient symptoms, the size and location of the lesion, the age and activity level of the patient, presence of a loose body, and presence or absence of generalized arthritis in the remainder of the knee. Due to the lack of blood supply to the articular cartilage, chondral injuries will not heal similarly to cuts in the skin or broken bones. Treatment is aimed at controlling symptoms of chondral damage, smoothing the remaining joint surface to prevent re-aggravation, or restoring the cartilage surface through use of grafts or in-growth of “cartilage-like” scar tissue into the damaged cartilage surface.
For older, lower-activity demand patients with minimal symptoms, non-operative treatment is usually recommended. Non-operative treatment involves rest and activity modification, weight loss to reduce stress on the knee, anti-inflammatory medicine, cortisone injections, and possibly viscosupplementation (artificial joint fluid) injections.
For younger, active patients, or those who fail to have lasting relief from non-operative treatment, surgery may be recommended. The type of surgical procedure depends on numerous factors including patient age, size and location of the lesion, and prior surgical treatments. In one commonly performed procedure, called “chondroplasty,” the surgeon arthroscopically smoothes the shredded or frayed articular cartilage to remove loose flaps that can irritate and inflame the joint. Another more involved procedure called microfracture involves creating several small holes in the bone at the base of the chondral damage to encourage in-growth of cartilage-like scar tissue to fill the damaged area.
Grafting of cartilage plugs into the area of chondral damage may be indicated in certain cases. These grafts may be taken from a non-weight bearing portion of the patient’s own knee (termed autografts) or donor cartilage plugs may be used for larger lesions (termed allografts). Larger lesions may benefit from a staged procedure known as “autologous chondrocyte implantation” where a sample of the patient’s cartilage is removed arthroscopically and sent to a lab where the cartilage cells are grown in a cell culture for 3-6 weeks. These cells are then re-implanted during a second surgical procedure.
For more information, visit http://orthoinfo.aaos.org/topic.cfm?topic=A00422.