This is a 15-year old male who presents with left hip 
pain for one hour.  He was sprinting during a track and 
field meet.  He experienced a sudden pain in his left 
hip while running through a turn to the left.  He noted 
cramping in his left leg as well.  He denies falling onto 
his hip.  His pain is now somewhat better, and he is 
able to stand.  He reports a one week history of 
suffering from a left hip strain.  He has been doing 
stretching exercises and applying ice to his hip.  His 
past history is unremarkable.
     Exam VS:  T37.3 (oral), P90, R18, BP 128/69.  
Weight 59 kg.  He is of slim build and normal stature.  
He is not obese.  He is alert and in no distress.  He is 
able to stand.  There are no signs of external trauma 
such as abrasions or bruises.  He has some tenderness 
to palpation of his left hip.  His internal and external 
rotation about the hip are normal, and there is minimal 
pain.  Most of pain is elicited with flexion of his hip.  His 
flexion is limited to approximately 45 degrees.  There is 
no warmth about the hip noted.  There are no 
deformities or tender areas along the long bones.  
Neurovascular testing distally is normal.
     Radiographs of his hips are obtained.

View hip radiographs.

     What would we expect to see on his radiographs?  
His history indicates that his injury was not caused by 
an impact.  A prolonged stress history is present, which 
may have been exacerbated by an acute stress 
precipitating the injury.  Such a history may be seen 
with small avulsion fractures (refer to Case 12 in 
Volume 2, Hip Pain in a Hefty 13-Year Old), a slipped 
capital femoral epiphysis (refer to Case 10 in Volume 2, 
Thigh and Knee Pain in an Obese 10-Year Old), or a 
pathological fracture among other things.
     This hip radiograph shows a bony fragment superior 
and lateral to the left hip joint.  This is an avulsion 
fracture of the left superior iliac spine.  Such avulsion 
fractures of the pelvis commonly occur during athletic 
competition.  These occur at the sites of muscle 
insertion into the pelvis.  Extreme muscle contraction 
forces pull at the insertion site.  This may cause 
microfractures, resulting in pain and weakening such as 
in Osgood-Schlatter's disease of the tibial tuberosity.  
Our patient exhibited symptoms of this type of 
preceding injury with his hip strain for one week 
preceding the avulsion fracture.  The three common 
sites of avulsion fractures of the pelvis are the anterior 
inferior iliac spine (insertion of rectus femoris), anterior 
superior iliac spine (insertion of sartorius), and the 
ischial tuberosity (insertion of multiple hamstrings).
     Of the common types of pelvic fractures (pelvic ring 
fractures, acetabular fractures, iliac wing fractures, 
etc.), avulsion fractures are the most benign.  These 
can usually be treated on an outpatient basis with 
crutches, analgesics, and modified activity.  
Spontaneous recovery usually occurs within 4 to 6 
weeks.  Occasionally, surgical intervention is required 
to remove painful fragments or to regain anatomic 
fixation.

References
     Bachman D, Santora S.  Orthopedic trauma.  In:  
Fleisher GR, Ludwig S (eds).  Textbook of Pediatric 
Emergency Medicine, third edition.  Baltimore, William 
& Wilkins, 1993, pp. 1266-1267.
     McCarthy RE.  Fractures of the pelvis.  In:  Letts RM 
(ed).  Management of Pediatric Fractures.  New York, 
Churchill Livingstone, 1994, pp. 453-482.