Introduction

Osteochondritis dissecans is a condition that causes ankle pain and stiffness (Fig. 1). Osteochondritis dissecans can affect all age groups and usually follows a twisting injury to the ankle such as an ankle sprain. Osteochondritis dissecans is a loss of blood supply to a segment of bone and cartilage in the ankle and may result in a small fracture or collapse of the joint surface.

Anatomy

The talus is one of the large foot bones that help form the ankle joint (Fig.2). Osteochondritis dissecans occurs at the top of the talus. Depending on how the ankle injury happened, the condition can occur on the sides of the talus.

The top of the talus is part of the ankle joint and is covered with articular cartilage (Fig. 3). Articular cartilage is the white, slippery material that covers all joint surfaces. The articular cartilage on the talus is about one-eighth of an inch thick and allows the bones of the ankle joint to slide against each other without much friction.

Causes

Most cases of osteochondritis dissecans are caused by actual chip-type fractures (Fig. 4). These fractures often occur with severe ankle sprains. The side of the talus the chip is on depends on how the ankle was twisted during the initial injury.

The chip fracture can vary in size and severity. If the bone underneath the cartilage is crushed or cracked and the articular cartilage is left intact, the fragment is less likely to move. However, if the articular cartilage is broken, bone chip fragments may move out of position hindering the healing process.

Because the bone chip is separated from the rest of the talus, blood vessels traveling to the chipped fragment are torn and the blood supply to fragment is lost. If the fragment displaces, these blood vessels cannot grow back. The fragment looses its blood supply and dies. This makes healing less likely.

Symptoms

Osteochondritis dissecans includes symptoms similar to ankle sprain injuries. You may feel swelling and pain and have difficulty placing weight on the ankle. Continued problems with the fragment may cause more swelling and a generalized ache in the ankle. You may also feel a catching sensation with the ankle in certain positions. This is caused by the chip getting caught in the ankle joint as it moves. Over time, osteochondritis dissecans can result in severe arthritis.

Diagnosis

The diagnosis of osteochondritis dissecans may be suggested by your medical history and physical examinations. X-rays of your ankle will usually show a problem on the top of the talus (sometimes called the talar dome). Special tests such as computerized axial tomography (CAT scan), or magnetic resonance imaging (MRI) may be necessary to determine the full extent of the area involved.

Treatment

Conservative Treatment

Treatment for osteochondritis dissecans depends on when the problem is discovered. If discovered immediately after a twisting injury to the ankle, immobilization in a cast for six weeks may be suggested to see if the bone injury heals. You may need to keep weight off the foot and use crutches during this period of immobilization.

Surgery

If osteochondritis dissecans is not recognized early, the bone fragment may not heal and may continue to cause problems. Surgery may then be required to treat your symptoms.

Surgery usually involves removing the loose fragment of cartilage and bone from the ankle joint and drilling small holes in the injured bone. When the fragment is removed, a defect shaped like a small crater is left in the talar dome (Fig. 5). Holes are drilled in this area allowing new blood vessels to grow and helping scar tissue to form to fill in the area. Eventually this new scar tissue smoothes out the defect and allows the ankle to move more smoothly.

The surgery can be performed in several ways. In some cases the surgery can be done using an arthroscope. An arthroscope is a special miniature camera that can be inserted into the joint through a very small incision. Through other small incisions, special instruments can be inserted into the ankle. While the surgeon watches on a TV screen, the fragment can be removed and the defect drilled.

The ankle is a small joint, and the arthroscope may have difficulty getting into certain areas of the joint. If the defect is difficult to reach with the arthroscope, an open incision may be required. This incision is usually made in the front of the ankle to allow the surgeon to see into the joint. Again, special instruments are used to remove the bone fragment and drill the injured area.

Rehabilitation

If your surgeon recommends nonsurgical care using a cast or cast boot, you may be on crutches for up to six weeks. During follow-up office visits, X-rays will probably be taken so that the surgeon can follow the healing of the fragment and determine whether surgery will be necessary.

If surgery is required, it will take about eight weeks before the bones and soft tissues heal. You will be placed in a cast or cast boot during this period to protect the bones while they heal. You will probably need crutches as well. A physical therapist may help you learn to use your crutches.

You will probably wear a dressing for a week following the procedure. The stitches will be removed 10 to 14 days from surgery. If your surgeon used dissolvable stitches, these will not need to be removed.