Osteochondral Fractures of the Knee and Ankle

Injuries to the knee and ankle are very common in sports. The most common injuries include ankle sprains and ruptures of the anterior cruciate ligament in the knee. A less common injury, however, is an osteochondral fracture, which means that the cartilage covering the end of a bone in a joint (articular cartilage) is torn. The fracture creates bone or cartilage fragments that can range in size and in depth. This injury, which occurs primarily in children and adolescents, can lead to the development of osteoarthritis. Osteochondral fractures are frequently found on the weightbearing surfaces of the femur (thigh bone) at the knee joint. They also can occur under the patella (kneecap). These fractures commonly involve both the articular cartilage and the bone underneath. Usually, only one fracture occurs at a time, but sometimes more than one occurs at the time of injury.

These fractures also can occur in the ankle along the talus (bone below the shin bone that forms one third of the ankle joint).³ An osteochondral fracture that occurs on the outer side of the talus usually only tears a piece from the surface of articular cartilage. An injury to the inner side more often results in a crater-like lesion that involves bone underneath the cartilage.

How does the injury happen?
In the knee, osteochondral fractures typically result when you twist your knee badly. Direct trauma (sudden, forceful injury) to the inner or outer part of the femur at the knee can lead to these lesions. Symptoms include immediate pain and swelling of the joint and pain with weightbearing when you stand up or start to walk.

In the ankle, these fractures occur by a force directed from the joint surface of the tibia (shin bone), across the joint, and into the talus. Most osteochondral fractures to the outer side of the talus result from trauma. Injuries to the inner side of the talus may result from a recurring ankle injury, such as a sprain.³ The signs and symptoms of injury may be minimal, but they can include swelling, bruising, grating feeling with movement, weakness, or instability of the joint.

Diagnosis
The doctor may begin your evaluation by asking about your medical history, conducting a physical examination, and taking the appropriate x-rays. Often, the fracture is difficult to see on the x-rays, so the doctor may need to take special images, such as a computed tomography (CT) scan or magnetic resonance imaging (MRI), to closely evaluate your injured knee or ankle.

Treatment
How the doctor treats your injury depends on the stability of your fracture. If the fracture fragment is well attached to the bone, you wear a cast until the fracture heals in place. If the fragment is not well attached or many small fragments are loose within the joint, they may be removed through arthroscopic surgery (tiny camera and instruments inserted into the joint).² Because loose fragments in the joint can cause your joint to catch and lock, they need to be removed.

Fragments that can be fixed through surgery are usually at least the size of a dime. The doctor drills the bone under the damaged cartilage to cause a small amount of bleeding. The blood stimulates the growth of new cartilage (called fibrocartilage), and the area is allowed to heal. Sometimes instead of drilling, the doctor may transplant cartilage from one area of the joint to the other. In the knee, the cartilage graft is taken from a non-weightbearing part of the knee and moved to the weightbearing part that is injured. This operation is similar to transplanting the hole on the putting green of a golf course. When the flag stick is moved from one portion of the green to another, a hole is dug in the new position, and the grass and soil underneath (similar to the cartilage and bone underneath) are moved to fill the old hole. The operation can be done through an arthroscope or through a small incision. The fibrocartilage that forms in the area from which the graft was taken can withstand the stress placed on that portion of the joint.

Osteochondral fractures of the ankle usually do quite well once treated. In a survey taken at The Hughston Clinic, 90% of patients had no pain or swelling with use of the ankle 10 years after treatment.

Depending on where the fracture occurred, injuries of the knee also do fairly well after treatment. For instance, a fracture underneath the patella may cause minimal harm with activities such as bending your knees or going up and down stairs. If the fracture occurs in a weightbearing surface between the femur and tibia, then arthritis or constant swelling and pain with weightbearing can occur. Fortunately, these injuries are rare and are not a major cause of arthritis in the general population.

Timothy F. Peters, D.O., M.S., and Champ L. Baker, Jr., M.D. 
Columbus, Georgia 

Further reading
1. Berndt AL, Harty M. Transchondral fractures (osteochondritis dissecans) of the talus. J Bone Joint Surg Am. 1959;41:988-1020.
2. Canale ST, Belding RH. Osteochondral lesions of the talus. J Bone Joint Surg Am. 1980;62:97-102.
3. Shea MP, Manoli A II. Osteochondral lesions of the talar dome. Foot Ankle. 1993;14:48-55.
4. Sponseller PD, Beaty JH. Fractures and dislocations about the knee. In: Rockwood CA Jr, Wilkins KE, Beaty JH, eds. Fractures in Children. 4th ed. Philadelphia, PA: Lippincott-Raven; 1996:1231-1329.
5. Baker CL Jr, Morales RW. Arthroscopic treatment of transchondral talar dome fractures: a long-term follow-up study. Arthroscopy. 1999;15:197-202.