Suffering from Osgood - Schlatter 's disease John only recently began jumping again in preparation for the event .
Osgood - Schlatter 's disease is a painful swelling of the bump on the upper part of the shinbone just below the knee .
Suffering from Osgood - Schlatter 's disease , a painful swelling of the bump on the upper part of the shinbone just below the knee , John only recently began jumping again in preparation for the event .