Bone or bone tissue is a type of connective tissue that forms the skeletal system. Bone has a complex structure and exceptional mechanical properties. The skeletal system is subject to a variety of loads, i.e., it is affected by various mechanical forces. Bone healing is a physiological process of bone regeneration after damage or fracture. There are numerous fracture classifications, and one of the most detailed is that by the Association of the Study of Internal Fixation whose acronym AO represents the most important organization that has for over 50 years worked on development of all fracture treatment protocols. Bone healing can be direct and indirect. Indirect (secondary) healing is "natural bone healing" that occurs with relative stability when there is some movement at the fracture site. Direct (primary) healing requires absolute stability, i.e., when complete absence of movement of fracture fragments is achieved surgically, by interfragmentary compression. A procedure in which fixation is achieved surgically is called osteosynthesis. Successful osteosynthesis is preceded by reduction that can be anatomical or functional, depending on the adaptation of fracture fragments, and direct (open) or indirect (closed), depending on the type of fracture site exposure. Osteosynthesis is achieved by various implantable devices such as screws, plates, intramedullary nails etc. There are various factors that affect the fracture healing process. Local factors are connected to the complexity of injury and treatment methods, whereas systemic factors include patient health, drug administration, smoking, alcohol etc.