**3.2 Smoking**

It was reported that smoking and its components significantly affect the fracture union especially the tibial shaft fractures, spinal, and foot and ankle fusions. The smokers expressed a 40% increased time to union compared to non-union smokers [24]. Cigarette smoking contains over 4000 toxins such as nicotine, carbon monoxide, nitrosamines, benzenes, aldehydes, and hydrogen cyanide that can inhibit the proliferation of precursor cells, fibroblasts, red blood cells, and macrophages [25].

## **3.3 Diabetes mellitus**

Diabetes mellitus is the other effective factor in bone healing. Diabetes mellitus affects the skeletal system and increases the chance of osteoporosis and fragility fractures, delays bone healing rates, and reduces bone repair quality [26].
