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Knee News

Bioabsorbable Fixation Not Quite Up to Snuff for OCD of the Knee

Adults with osteochondritis dissecans (OCD) of the knee are advised to have surgery because their bones are fully grown. Their symptoms of pain, swelling, catching, and locking of the joint won't go away unless the bone fragments are reattached or removed. Younger patients with OCD have a chance for healing because there is a better blood supply to the growing bone and less fibrous tissue already formed between the bone fragments.

Osteochondritis dissecans (OCD) is a disorder of the bone with a fracture in the joint surface that doesn't heal naturally. The problem can affect the elbow, ankle, or knee. OCD of the knee mostly affects the rounded end of the lower femur (thigh bone). This area is called the femoral condyle of the knee. Like most joint surfaces, the femoral condyles are covered in articular cartilage. Articular cartilage is a smooth, rubbery covering that allows the bones of a joint to slide smoothly against one another.

The problem occurs where the cartilage of the knee attaches to the bone underneath. The area of bone just under the cartilage surface is injured, leading to damage of the blood vessels to the bone. Without blood flow, the area of damaged bone actually dies. This area of dead bone can be seen on an X-ray and is sometimes referred to as the osteochondritis lesion.

The lesions usually occur in the part of the joint that holds most of the body's weight. This means that the problem area is under constant stress and doesn't get time to heal. It also means that the lesions cause pain and problems when walking and putting weight on the knee. It is more common for the lesions to occur on the medial (inside) femoral condyle, because the inside of the knee bears more weight.

In the skeletally mature adult, the best treatment remains unclear. Surgeons try to preserve the bone fragment(s) by reattaching them to the bone with screws, pins, nails, darts or some combination of these fixation devices. Even with surgery, OCD can lead to future joint problems, including degenerative arthritis and osteoarthritis.

Newer bioabsorbable fixation is now available. But the results of using this type of fixation that gets absorbed by the body (and doesn't have to be removed) are unknown. In this report, surgeons from the Mayo Clinic Orthopedic Department share the results of using bioabsorbable fixation in 18 adults with osteochondritis dissecans (OCD) of the knee. Most of the patients (14 of the 18) were men. All patients included in the study were between the ages of 14 and 39.

Arthroscopic exam of the knees confirmed unstable lesions with crater-like holes in the joint and loose fragments of cartilage and/or bone. Surgery to move the fragments back into place (a procedure called reduction) and fix them in place was done by one of six different Mayo surgeons. Everyone was followed for at least a full year. Some patients remained in the study follow-up for more than 10 years. They used three different ways to measure the results: clinical tests, improved function, and X-rays to document the status of the bone.

In two-thirds of the group, the fragment adhered to the bone in what is referred to as fragment union. One-third of the group ended up having the loose piece taken out in a separate surgery later. Bioabsorbable nails (with no threads like the screws) had a tendency to break or back out. When that happened, the patient had a new hole in the joint surface of the femur and sometimes another one on the tibial (lower leg bone) side.

The authors concluded that in all honesty they couldn't recommend bioabsorbable fixation for OCD lesions in skeletally mature adults. There were too many problems and a low healing rate. This treatment approach clearly is not superior to others such as using metal fixation or drilling tiny holes into the joint surface to stimulate healing, a procedure called microfracture.

Efforts to improve results with bioabsorbable fixation devices will continue because metal screws can also back out, loosen, damage the joint surface, and require a second surgery to remove them. Bioabsorbable fixation has the added advantage of gradually transferring stress to the bone as the material dissolves. Additional disadvantages include failure to dissolve or disintegration at different rates within the bone. Studies are needed to see if this type of unpredictable or uneven absorption makes any difference in the final results.

Kendra L. Millington, et al. Bioabsorbable Fixation of Unstable Osteochondritis Dissecans Lesions. In The American Journal of Sports Medicine. October 2010. Vol. 38. No. 10. Pp. 2065-2071.


*Disclaimer:* The information contained herein is compiled from a variety of sources. It may not be complete or timely. It does not cover all diseases, physical conditions, ailments or treatments. The information should NOT be used in place of visit with your healthcare provider, nor should you disregard the advice of your health care provider because of any information you read in this topic.
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