Introduction
In osteochondrosis dissecans, part of the bone underneath the articular cartilage dies, allowing it to detach and become loose in the joint cavity (dissection). The exact causes leading to this disease are not yet fully understood, but repetitive trauma or overloading as well as circulatory disorders of the bone seem to play a role. Infections of the bone, on the other hand, do not play a role in the development of osteochondrosis dissecans. The disease is therefore an aseptic bone necrosis. Osteochondrosis can occur in joints all over the body or, in children, in growth joints.
Stage 1
In the first stage the bone begins to become lytic due to unknown processes, i.e. it begins to dissolve. This stage is usually not visible in the X-ray image because the bone is not interrupted at any point. However, if an MRI of the knee joint is made, small osteolyses can be seen in it as foci that are distinct from normal bone density.
In addition, there is a bone marrow edema, i.e. a small accumulation of fluid in the bone tissue, which impresses as brightening in a water-weighted sequence of the MRI. The cartilage is still intact and fulfils its mechanical function in the joint, therefore symptoms are rather weak. It is possible that a slight pain on exertion may occur. At this stage, the therapy of choice should be chosen conservatively. The further course of the disease is observed, and there may be phases in which the affected joint should be spared from heavy strain.
Stage 2
As the disease progresses, the bone is increasingly fragmented into several fragments. The necroses of the bone become larger as numerous bone bundles are broken down or collapse. In this case one can speak of microfractures.
At the same time, the body reacts to the degradation by initiating processes to stabilize it. The damaged areas below the cartilage are reinforced by sclerotherapy. This means that more bone tissue is stored in this area.
In the x-ray image, this sclerosis can be seen as a lighter line below the joint cartilage. At this point, the risk of further damage is greater than in stage 1. To prevent damage to the cartilage, a ban on sports is usually imposed to give the body time to regenerate the defects.
There is a good self-healing tendency, especially in young people up to puberty, whose growth joints are still open. Crutches can be prescribed as a support. If the pain symptoms get worse despite a break from sport, the indication for arthroscopy is given.
The cartilage can be assessed. In stage 2 it is still intact. The physician can then drill through the cartilage to the bone and stimulate the tissue to further new formation.