My son has had one and is scheduled to have one every 18 months to 2 years. Our GI said that it is common for kids with Crohn's to have low bone density (especially if they are not processing/absorbing vitamin D well). Alex' Vitamin D levels are conistently low - he had his first last year - and the doctor said his bone density was on the low side (though the tech who did the scan said he looked great!). When I asked what that meant, she said that he was more suspectible to bone breaks (to which I had to swallow hard!).
I asked her - does that mean he shouldn't play ice hockey? She's from India and asked us, "Well... as long as he's not getting hit hard, he should be okay..." Alex and I just looked at each other and say, "OK". She obviously doesn't know alot about ice hockey... We (Alex and I) talked about the results, but he said he'd rather play with the possibility of getting a broken bone, than not play. (touch wood - thank you God - no major injuries!)... Whew...