This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
The most impoant cause of Nonunion of fracture of - humeral shaft is 
Select and explain. 
A. Comminuted fracture, B. Compound (Open) fracture, C. Overriding of fracture ends, D. Distraction at fracture site
D: Distraction at fracture site
Answer: D: Distraction at fracture site 
Explanation: D i.e. Distraction at fracture site Fracture shaft humerus is the easiest of major long bone fractures to be treated by conservative methods. And the most common cause of delayed union or nonunion is distraction at fracture siteQ due to gravity and weight of plaster.