CAN’T stand hobbling around in your cast? Perhaps there’s a way out. Mice with broken legs seem to be healing three times faster than normal, thanks to a protein that makes stem cells divide.

Jill Helms, Roel Nusse and colleagues at Stanford University in California drilled small holes into the shin bones of mice, then injected Wnt proteins, which prompt bone stem cells to divide. Three days later, bone growth was three times greater than in mice injected with a placebo (Science Translational Medicine, DOI: 10.1126/scitranslmed.3000231).

This approach stimulates bone growth temporarily and so might be better than adding …