What Causes Recurrent Fibromatosis In A Child?

my son has fibromatosis in his right hand 4th metacapal in 2005 (he was 8 years old that time). 1st surgery done in 2005, but recur in 2008. 2nd surgery in 2009 for excision & autograft bone graft. Today (8/12/2010), appontment with dr. found from MRI that it recur in the tissue of 3rd metacapal of right hand. I am very worry about this, why keep recurring?when this will stop? he is now 13 years old, will this stop after he stop growing?