Fracture healing is a complex physiological process caused by interaction of cellular elements, cytokines and signaling proteins, which results in the formation of new bone. There is for now no universally accepted approach to evaluate the progression of fracture healing. Typically, a fracture is considered as a delayed-union when the bone has not united within a period of time that would be considered adequate for bone healing. Delayed-union suggests that union is slow but will eventually occur without additional surgical or non-surgical intervention, whereas non-union is defined as the cessation of all reparative process of healing.