The plastic pitch won't help, far less forgiving on impact than grass, we are training our M&Js on plastic at the moment, as the grass surfaces are so poor at the moment. We don't risk any sort of contract training or practice matches but focus on skills and touch to keep them sharp, when they fall over it seems to have more impact than the grass surfaces, they bruise as well which rarely happens on grass.
BillyV of the Barnet Cheetahs has broken both arms if I recall correctly. There has to be a factor in that, either genetic or playing conditions, or acts of god....