A study published in Developmental Cell has revealed that a fractured arm bone in newborn mice can rapidly realign through a previously unknown mechanism involving bone growth and muscle contraction.
The findings provide new insights into how human infants and other young vertebrates may repair broken bones and pave the way for more effective treatment strategies.
“Evolution has created a robust mechanism of bone regeneration, which may explain how wild animals can survive traumatic bone injuries,” said senior study author Elazar Zelzer of the Weizmann Institute of Science. “Further investigation of the newly found regeneration program could lead to alternative approaches for the treatment of fractures that do not respond well to current practices.”
Zelzer and his team suspected that a better understanding of natural regeneration in infants could help to improve interventions for fractured bones in adults. In the new study, the researchers found that a fractured arm bone in newborn mice rapidly realigned through substantial movement of bone fragments rather than through bone remodelling – a slower process involving the simultaneous formation of new bone on one side and erosion of existing bone on the opposite side.
“This finding challenges the traditional view of fracture healing and introduces an entirely new stage of bone repair to the classical four-stage model,” Zelzer said.
The realignment process was driven by bone growth, which acted like a mechanical jack to generate the opposing forces required to straighten the two bone fragments. Treatment with a drug that paralysed the muscles surrounding the fracture prevented normal bone growth and bone realignment, suggesting that muscle contraction plays a critical role in the repair process.
“Integrating this new knowledge into the current approach may improve future treatment,” added Zelzer. “For example, treatment may include age-based protocols and shorter periods of rigid immobilisation to allow participation of muscle force in the healing process.”
Rot, C., Stern, T., Blecher, R., et al. (2014) A mechanical jack-like mechanism drives spontaneous fracture healing in neonatal mice. Developmental Cell 31(2), 159