Elbow Injuries; Elbow Joint; Fracture Fixation, Internal; Humeral Fractures; Joint Deformities, Acquired; Postoperative Complications; Child; Child, Preschool; Elbow Joint/diagnostic imaging; Elbow Joint/physiopathology; Elbow Joint/surgery; Female; Fracture Fixation, Internal/adverse effects; Fracture Fixation, Internal/methods; Humans; Humeral Fractures/diagnosis; Humeral Fractures/diagnostic imaging; Humeral Fractures/surgery; Japan/epidemiology; Joint Deformities, Acquired/diagnosis; Joint Deformities, Acquired/etiology; Joint Deformities, Acquired/physiopathology; Joint Deformities, Acquired/prevention & control; Male; Postoperative Complications/diagnosis; Postoperative Complications/etiology; Postoperative Complications/physiopathology; Postoperative Complications/prevention & control; Radiography/methods; Range of Motion, Articular; Recovery of Function; Retrospective Studies; Treatment Outcome