Most authors recognize the distinction between osteochondritis of the center or the primary nucleus (Kohler disease) and osteochondritis of the secondary ossification center at the lower pole (Sinding-Larsen - Johansson disease). Kohler disease can also refer to navicular avascular necrosis.

The diagnosis of osteochondritis of the patella can only be placed when the x-ray is definitely accompanied by clinical symptoms. 

The early form is less common than the later-onset Sinding-Larsen disease. There is a slight male predominance. The early form occurs between 5 and 7 years, late between 9 and 14 years, in puberty. They are quite frequently bilateral.

It has been associated with apophysitis tibialis anterior and to a lesser extent with avascular necrosis at other locations. 

Case courtesy: Prof. Fabio Denicolò.