From the Journal of Paediatric Orthopaedics is a review of 228 apophyseal avulsions of the pelvis.  49% were from the anterior inferior iliac crest (AIIS), 30% ASIS, 11% ischial tuberosity, 10% iliac crest. The majority (97%) were treated non operatively. The most troublesome group was the AIIS with ongoing pain.  Failing to heal was most seen with fragments more than 20mm displaced and/or of the  ischium.  They concluded that most cases are treated without surgery, and the reasons to operate are displaced AIIS fragments or gross displacement.

This is an avulsion of the anterior superior iliac crest (ASIS).  It has moved 18mm and yet is expected to heal well. Reasons to operate are if the adjacent nerve is irritated, if the fragment more displaced, or if it came from closer to the hip joint (AIIS).

ref: J Pediatr Orthop 2015 Sep;35(6):617-23   

Mr David Mitchell