What are the long term consequences of osgood-schlatter's?

Not much : Osgood-shlatter's disease occurs during rapid growth in adolescence. The usual long term consequence is a smal non painful bump on the knee. It's really not so much a disease as a developmental occurrence. The joint is spared and long term negative effects are rare.

Usually none: Most children outgrow osgood-schlatter disease as soon as their growth plates fuse. For boys this is around 16 years of age and girls about 14. Sometimes there can be a painful ossicle remaining behind which may need to be excised. This is rare.