A detailed case history of a 6 years old child, including biochemical and radiological examinations, has been presented. The disease started with a commonplace contusion of the patella and rapidly progressed after arthrotomy. Dihydroxy-aluminium-natrium carbonicum was applied as well as the low calcium and phosphorus diet. After 4 weeks of treatment, the joint recovered its correct contours; and after further 7 months, only vestigial calcification was observed.