What is osteochondritis dissecans of the knee in children?
Osteochondritis dissecans (OCD) is an acquired condition affecting a section of bone in the knee just beneath the joint cartilage. It is believed that one of the causes of OCD is repeated microtrauma, which causes a stress fracture of the bone and consequently softening of the overlying joint cartilage. Because the stress is repeated, healing does not occur at the fracture site; instead, the bone becomes soft and necrotic, and over time, together with the cartilage above it, becomes unstable in its bed or even separates completely as a loose body within the joint. Perhaps because they are more involved in sports activities, OCD of the knee occurs four times more often in boys than in girls. OCD sometimes develops in both knees at the same time. If OCD of the knee is not recognised and treated in time, further deterioration of the bone and cartilage in the joint occurs, which can ultimately lead to an abnormal relationship between the joint surfaces and earlier wear of the knee – the development of osteoarthritis.
How is osteochondritis dissecans of the knee diagnosed in children?
The clinical picture of knee OCD in children is nonspecific. Children usually complain of pain related to activity, or restricted knee movement together with occasional swelling. Sometimes children report that something is "moving around" inside the knee, which may be a fragment of detached cartilage shifting within the joint. On clinical examination at a paediatric orthopaedic clinic, tenderness is usually found over the site of the OCD lesion if it is accessible to palpation. Range-of-motion testing of the knee may reveal a catching sensation. If knee OCD is suspected, an X-ray in two views should always be taken, along with an additional so-called tunnel view of the knee. On X-ray, OCD appears as a separated, elongated fragment of bone within an arched bed. Alongside X-ray, when knee OCD is suspected, the child should also be referred for an MRI scan of the knee. The most important information assessed on knee MRI includes: the condition of the joint cartilage (intact or disrupted), the condition of the bone beneath the cartilage (presence of cystic changes or fluid tracking beneath the fragment), assessment of OCD stability, and any associated knee pathology. For example, an irregular, discoid meniscus often causes OCD in the knee.
How is osteochondritis dissecans of the knee treated in children?
The choice of treatment for knee OCD in children depends mainly on the degree of bone and cartilage damage on one hand, and the child's bone maturity on the other. It is therefore very important to correctly assess the child's bone maturity, that is, how much growth potential remains. In younger children with an open growth plate, there is a good chance that OCD will heal conservatively, without surgery. In that case, sports activities or any repeated trauma to the knee are restricted for six months to a year, with follow-up carried out using new MRI scans. Vitamin D supplementation is recommended during this period. However, if a follow-up MRI shows an unstable OCD lesion in its bed, or a loose fragment within the joint, or if the child is skeletally mature, surgery should be considered. Today, the standard of care is fixation of an unstable OCD lesion via knee arthroscopy with screws, or debridement of the OCD bed together with repair of cartilage damage, for example with microfracture. During knee arthroscopy, meniscal stability should also be assessed, and the meniscus repaired if it is unstable. Postoperative rehabilitation includes walking with crutches with gradual weight-bearing on the leg, and, if the meniscus was repaired, a gradual increase in range of motion. The prognosis in children is generally good once the OCD fragment is stabilised, as they have a high healing potential.
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