3D Printing Adjustable Stiffness External Fixator for Mechanically Stimulated Healing of Tibial Fractures

Table 2

Criteria for strain and fixation stability of the callus at different healing stages.

Classification of various healing processes [16, 17, 26]	Granulation tissue	Fibrous tissue	Cartilage	Immature bone	Intermediate bone	Mature bone	Cortical bone
	Primary healing; Direct bone repair without endochondral ossification			Secondary healing; Appropriate stability of the fracture site to maintain the biological healing response
	Inflammatory stage	Anabolic phase		Endochondral stage
				Catabolic phase
					Coupled remodeling
	Inflammatory response [5, 27]	Soft callus formation		Hard callus development	Remodeling
Fix condition [5, 18, 24, 25, 27, 28]	Absolute stability		Relative stability
Young’s modulus, (MPa) [17, 29]
Day [30]
Stiffness adjustment tolerance of the fixator