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
All of the following are types of avascular non-union except: 
Select and explain. 
A. Comminuted, B. Elephant foot, C. Torsion wedge, D. Atrophic
B: Elephant foot
Answer: B: Elephant foot 
Explanation: Classification of non-union:
 Hypervascular non-union:

Elephant foot (hypertrophic , rich in callus)
Horse foot (mildly hypertrophic , poor in callus)
Oligotrophic (non-hypertrophic, no callus)

Avascular non-union:

Torsion wedge
Comminuted
Defect
Atrophic