A multi-center cohort of children with newly diagnosed ALL was established with Pediatric Health Information System (PHIS) data from 43 freestanding children's hospitals from 1999 to 2011. 
Pediatric Health Information System (PHIS)
Patients with ON identified by International Classification of Diseases, Ninth Revision (ICD-9) code were followed for up to 5 years after index ALL admission for the presence of ON-associated orthopedic surgical procedures.



International Classification of Diseases, Ninth Revision (ICD-9)