There are two potential problem with close reduction and cast management of fracture supracondylar humerus. The first is loss of reduction and 2nd is increased swelling and potential development of compament syndrome, secondary to immobilization with the elbow in flexion. That's why admission to hospital is essential following reduction. Ref: Tachdjian's Pediatric Ohopedics 3/e, Page 2130-75, 2060; Rockwood and Green's Fracture in Children 6/e, Page 543-86.