Osteochondritis dissecans (OCD) is a relatively uncommon condition in which a part of articular cartilage, together with a layer of bone, becomes damaged and eventually detached from the end of a bone. Although OCD can occur in other joints of the body, this condition mostly affects the knee.
The knee is a hinged joint formed from three bones, the femur (thighbone), the tibia (shinbone) and the patella (kneecap). Where the bones meet they are covered with articular cartilage, a smooth connective tissue that allows them to slide over each other without friction. The bottom end of the femur is rounded, with the area of bone to the outside of the knee known as the lateral femoral condyle, and the area to the inside of the knee, the medial femoral condyle. Over eighty percent of cases of OCD are found on the medial femoral condyle, probably because this part of the knee bears more body weight.
Depending on the age at which this condition manifests, it is termed juvenile osteochondritis dissecans (JOCD) or OCD. The average age when symptoms first appear is between ten and twenty years old, although it can appear at any age.
Osteochondritis dissecans is caused by a reduction in the blood supply to the end of the bone, leading to the collapse of an area of bone. The cartilage overlying the area then becomes damaged and can eventually detach, along with a layer of bone to which it is attached. This is known as an osteochondritis lesion.
Although it not certain what conditions might lead to such a reduction in the blood supply, one theory is that repeated small and unnoticed injuries cause accumulated damage and when such damage is extensive enough, symptoms become apparent. Another possibility is that there is a genetic component and certain individuals are therefore susceptible to developing OCD. Currently males are two to three times more likely than females to develop OCD.
If a detached fragment stays in place, there may be no or few symptoms. If, however, it moves within the knee joint, symptoms may include:
- Aching pain, mild at the beginning, but worse with time and worse with movement
- A snapping sensation, caused by bone moving across a notched area of cartilage
- Knee locking or popping, which can be caused by a fragment getting stuck between the bones of the joint
- Weakness in the knee joint, possibly leading to an inability to bear weight
- Decreased range of motion
- Swelling and tenderness around the area
Your doctor will ask questions relating to your previous medical history, particularly any prior knee injuries. He or she will also ask about the symptoms being experienced, their onset, duration and severity. Your knee will be examined, during which time it will be moved and felt. You may be asked to perform certain movements in order to evaluate what causes pain.
You will probably have an x-ray taken, and possibly also CT or MRI scans. A combination of images will provide your doctor with a good view of the bones and soft tissues of your knee. If the OCD is in its early stages, a bone scan may be taken. This involves injecting a special dye into the blood, which attaches to rapidly changing bone, such as a fracture healing. The image taken after injection of the dye will provide information to assist the doctor with the diagnosis.
Osteochondritis dissecans can be graded, depending on the progression of the lesion:
- Grade I: Positive diagnosis, but the articular cartilage is still whole
- Grade II: Some damage to the articular cartilage is visible
- Grade III: There is a loose fragment, but it is still within the depressed area of bone
- Grade IV: The loose fragment has become dislodged and is elsewhere within the joint
Younger patients whose skeletons are still immature have the best outcome with non-operative treatment, although the decision will depend on the stability or looseness of the lesions (fragments). If the lesion is unstable, surgery might be necessary.
Older patients will almost certainly have to undergo surgery, as the OCD will not heal completely on its own.
Non-surgical treatment is usually tried for at least three to six months before surgery is considered.
- Rest: activity must be restricted and movement of the knee limited. This can be achieved with the use of a knee immobilizing brace, or a hinged and adjustable brace that can be set for a limited range of motion, and the use of crutches when walking.
- An ice pack on the knee, kept in position for fifteen minutes at a time, to reduce inflammation.
- Elevate the knee above heart level, whenever possible.
- The use of over the counter pain medication such as acetaminophen (Tylenol) and NSAIDs (Advil, Motrin, Aleve).
- Physiotherapy to gradually stretch and strengthen the knee and its supporting muscles, and increase the range of motion of the joint
When surgery is necessary, arthroscopy is preferred to open knee surgery as trauma to the knee is less and recovery times are quicker. Depending on the size and location of the fragment, the surgeon might:
There is currently an experimental technique being developed where articular cartilage is grown from cartilage cells (chondrocytes) and then implanted.
Following surgery, a continuous passive motion machine may be used to help prevent stiffness. You will have to avoid putting weight on the leg for up to six weeks, and up to four months if you have had a tissue transplant. Using a walker or crutches will help you get around. A physiotherapist will work with you, initially to relieve pain and reduce swelling, and then to introduce a program of exercises designed to restore range of motion, flexibility and strength to the knee joint.
- Drill small holes at the site of the damage, in an attempt to stimulate a new supply of blood to the area
- Secure the fragment back in position using pins or screws, which may need subsequent removal.
- Remove the fragment from the joint
- Graft another piece of bone and cartilage onto the damaged area of bone. This might be tissue from your own body (usually taken from a non-weight-bearing area of the joint) or from a donor.
The younger the patient, and the smaller and more stable the lesion, the better the outcome will be. It is possible, and more likely in older patients, that a diagnosis of osteochondritis dissecans will result in eventual degenerative or osteoarthritis of the knee.