TABLE 6.

Comparison of histological findings between atrophic—hypertrophic non‐unions

	Atrophic	Hypertrophic
Type of tissue
Fibrocartilaginous tissue	33, 34	34, 46
Fibrous tissue	16, 32, 34	34, 36
Cartilaginous tissue	16	32, 34, 45
Collagenous extracellular matrix/connective tissue	11, 13, 32, 33	32, 33, 45
Bone tissue	No ossicles 32 ; occasional bony islands 15 , 33 , 34 ; lack of viable osteoclasts and greater percentage of pericytes, CD31+ and reduced number of lymphocytes compared to induced membrane tissue 8 Mixture of lamellar and woven bone 16	No ossicles 32 , 36 ; bony islands 15 , 34 , 45 , 46
Necrotic bone	More prevalent 34	‐
Bone production	Predominantly via the endochondral route 34	Bone formation by both endochondral and intramembranous ossification 34
Cells	‐Generally oligocellular 32 ; ‐some areas acellular 33 ‐ Fibroblasts: majority of cells 11, 13, 33 ‐Osteoclasts: occasionally 33 or enhanced activity 13 ‐bipolar cells: majority of cells 33 ‐Cells with a stellate (possessed multiple cytoplasmic processes) or dendritic appearance 33 ‐Include MSCs, fibrocartilage cells and hyaline chondrocytes 15	‐More cellular 32 ‐Fibroblast‐like 36 ‐ Include MSCs, fibrocartilage cells and hyaline chondrocytes 15
Vascularization	Well vascularized 33 , 34 , 49 ; few vessels 11, 32	Well vascularized 34

As only reporting on studies published after our original review ¹ would provide an incomplete picture of the differences between atrophic and hypertrophic non‐unions, we include all relevant data regardless of publication date.

References highlighted bold: new references published after our original review. ¹