A mechanical Jack-like Mechanism drives spontaneous fracture healing in neonatal mice.
Treatment of fractured bones involves correction of displacement or angulation, known as reduction. However, angulated long-bone fractures in infants often heal and regain proper morphology spontaneously, without reduction. To study the mechanism underlying spontaneous regeneration of fractured bones, we left humeral fractures induced in newborn mice unstabilized, and rapid realignment of initially angulated bones was seen. This realignment was surprisingly not mediated by bone remodeling, but instead involved substantial movement of the two fragments prior to callus ossification. Analysis of gene expression profiles, cell proliferation, and bone growth revealed the formation of a functional, bidirectional growth plate at the concave side of the fracture. This growth plate acts like a mechanical jack, generating opposing forces that straighten the two fragments. Finally, we show that muscle force is important in this process, as blocking muscle contraction disrupts growth plate formation, leading to premature callus ossification and failed reduction.
Department of Molecular Genetics, Weizmann Institute of Science, P.O. Box 26, Rehovot 76100, Israel.
Chagai
C
Rot
Department of Molecular Genetics, Weizmann Institute of Science, P.O. Box 26, Rehovot 76100, Israel.
Tomer
T
Stern
Department of Molecular Genetics, Weizmann Institute of Science, P.O. Box 26, Rehovot 76100, Israel.
Ronen
R
Blecher
Department of Molecular Genetics, Weizmann Institute of Science, P.O. Box 26, Rehovot 76100, Israel.
Ben
B
Friesem
Department of Molecular Genetics, Weizmann Institute of Science, P.O. Box 26, Rehovot 76100, Israel. Electronic address: eli.zelzer@weizmann.ac.il.
Elazar
E
Zelzer
D000818:Animals; D001861:Bone Regeneration; D002146:Bony Callus / Q000254:growth & development* / Q000378:metabolism; D049109:Cell Proliferation; D017102:Fracture Healing; D005598:Fractures, Spontaneous / Q000628:therapy*; D020869:Gene Expression Profiling; D006132:Growth Plate / Q000254:growth & development / Q000502:physiology; D051379:Mice; D009119:Muscle Contraction / Q000502:physiology; D010012:Osteogenesis / Q000502:physiology*; D013312:Stress, Physiological