If your son has a Jakob fracture, then he has broken the round knob at the end of his humerus (upper arm bone) on the outside of the elbow/arm. The Jakob classification is a tool used by surgeons to help them determine how severe the fracture is and what type of treatment is necessary.
This classification scheme defines joint alignment (displaced vs. nondisplaced, malrotated, and whether or not the growth plate was affected). A displaced fracture is one that has separated. How much distance there is between the bone fragments is one indication of the severity of the fracture. There are three basic groups in this classification.
Jakob I means the fracture is not displaced or separated and can be treated with conservative (nonoperative) care. Jakob II fractures are displaced by more than two millimeters but without any rotation. Jakob III describes a fracture that is separated completely AND rotated. Jakob II and III elbow fractures of the lateral condyle will require surgery to reduce and stabilize them.
Since your son is currently in surgery, we can assume he has a Jakob type II or III type lateral condylar (elbow) fracture. As with other bone fractures, these kinds of elbow injuries can be treated with open or closed reduction. The type of fixation device used (plate, screw, pin, wire) depends on the location of the fracture, severity, and whether or not the growth plate has been disrupted.
Open reduction is typically required when there is significant malalignment and malrotation. While the patient is still under anesthesia, the surgeon makes sure the joint surfaces are lined up properly and the joint moves fully and freely. The surgery can be very complex and challenging in some cases but most children do just fine and heal quickly. We hope your son will be in this group!