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Predicting Healing in Osteochondritis Dissecans
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Posted on: 12/17/2008
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One-third of children with osteochondritis dissecans (OCD) will not heal with conservative (nonoperative) care. Is it possible to predict who might not benefit from the usual treatment of activity modification and immobilization? That's the focus of this study of children with OCD of the knee.
OCD is a problem that affects the end of the femur (thigh bone) at the knee. When it affects young children who are still growing, it is called juvenile OCD or JOCD. The joint surface is damaged and doesn't heal naturally. 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 to the blood vessels of the bone. Without blood flow, the area of damaged bone dies. This area of dead bone can be seen on an X-ray and is sometimes referred to as the osteochondritis lesion. A bone fragment with the layer of articular cartilage covering it detaches from the bone.
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. The lesion causes pain, swelling, locking or clicking at the knee. The patient has problems when walking and putting weight on the knee.
It is more common for the lesions to occur on the medial femoral condyle, because the inside of the knee bears more weight. The femoral condyle is the rounded end of the lower femur. Each knee has two femoral condyles, referred to as the medial femoral condyle (on the inside of the knee) and the lateral femoral condyle (on the outside).
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.
All of the children in this study had juvenile osteochondritis dissecans (JOCD). In children, the growth plates at the end of the bone are still open to allow for continued growth. Healing of osteochondritis lesions is important to prevent damage to the growth plate and to prevent altered bone growth.
Results of previous studies done on healing rates and the associated treatment approaches for JOCD in children have been mixed. The authors suspect this is because other studies included both stable and unstable articular cartilage defects. Unstable refers to the disruption that occurs in the surface of the articular cartilage. The chances for spontaneous healing when the articular surface is involved are low. Further damage is highly likely. Surgery is usually recommended.
But in stable JOCD, the articular cartilage is intact. It's not uncommon to wait six months and see if healing occurs on its own. The knee may be immobilized in a brace or cast, and the child's activities are restricted (e.g., no sports). But many of these children end up in surgery six months later when healing doesn't occur. If physicians could predict which children might need surgery, it could save the child and the family the six months' worth of stress waiting and wondering if the knee will heal.
In this study, the physicians used a special statistical model to predict the healing response of stable knee JOCD in children and young teens. Predictive factors tested included age, lesion size and location, symptoms, and sex (male or female). The lesions were examined before and after treatment using X-rays and MRIs.
Treatment consisted of six to 12 weeks of immobilization (long leg cast). This was followed by wearing a special brace that allowed weight-bearing. The brace can be adjusted to offload the affected part of the knee. As the lesion healed, each child was allowed to increase weight-bearing and activity level. When the lesion was completely healed, then full participation in sports activities without bracing was allowed. This process of advancing back to full activity took weeks to months.
Everyone's case was reviewed at the end of six weeks. The children were divided into two groups: those who showed signs of healing (or were healed) and those with no signs of healing. One-third of the group failed to progress toward healing. All lesions in this group were on the medial femoral condyle. The other two-thirds were either completely reossified (restored bone growth) or in the process of healing.
The data was then analyzed to see if they could find common factors among each group to help predict the outcome. It turned out that size does matter. The total surface (length and width) of the lesion combined together was a significant predictive factor. Children with swelling and/or other mechanical symptoms (e.g., locking or giving way of the knee) at the time of diagnosis were also less likely to experience sufficient healing.
In this study, lesions with an average size of 209 mm2 were more likely to heal compared with 288 mm2 in the failure-to-heal group. The authors compared these sizes to the results reported from other studies. There was a wide range of sizes reported with success/failure rates.
In other studies, the average surface area in young patients who healed with nonoperative treatment ranged from 152 mm2 to 309 mm2. The range for lesions that did not heal was from 194 mm2 to 436 mm2. Again, those other studies included both stable and unstable lesions, which could explain the wide ranges of results.
Although other studies have shown that younger children are more likely to heal, this study did not show an effect of age on healing progress. The reason for this difference was unknown. The authors suspect that the 34 per cent failure rate they had will be a larger percentage with long-term follow-up. They base this prediction on the fact that there were signal changes still seen on the final MRIs taken during the follow-up period. They intend to follow these children and see what happens over a period of years (rather than weeks to months).
The authors advise physicians treating children with juvenile osteochondritis dissecans to review MRIs at the time of diagnosis. If the articular cartilage is not disrupted (stable lesion), then a six-month trial of conservative care is advised. But parents should be warned there is a high risk of failure with no healing possible. The surgeon can use the size of the lesion and symptoms present at the time of diagnosis to predict healing potential.
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References:
Eric J. Wall, MD, et al. The Healing Potential of Stable Juvenile Osteochochondritis Dissecans Knee Lesions. In The Journal of Bone & Joint Surgery. December 2008. Vol. 90A. No. 12. Pp. 2655-2664.
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