Do broken bones become stronger after healing?

True or false?

This concept — that bone adapts to pressure, or a lack of it — is known as Wolff’s law. It’s the reason astronauts return with reduced bone density after floating in microgravity. And conversely, it explains why studies show that tennis players and fencers develop greater bone mass in their dominant arms and legs.

But this adaptive measure goes only so far. Despite one misconception, there is no evidence that a bone that breaks will heal to be stronger than it was before.

When a bone fractures, it begins the healing process by forming a callus at the fracture site, where calcium is deposited to aid rebuilding, said Dr Terry D Amaral, director of paediatric orthopedic surgery. In most cases, a plaster cast is applied to protect the fracture site. But because there is no weight or pressure on the limb, it becomes weaker — except at the site of the callus, where calcium is being deposited.

“The area that’s healing is undergoing rapid mineralisation, but because you can’t use it, the rest of the bone is demineralised,” Dr Amaral said.

As a result, there may be a brief period in the healing process when the fracture site is stronger than the surrounding bone. But they later reach equal strength, and the fracture site is no more or less likely to break again. Dr Amaral said that in studies in which healed bones were subjected to bending and twisting forces, the repaired bones were capable of breaking anywhere, including the fracture site. “They never comment that it’s stronger or weaker than the rest of the bone,” he said.

The verdict

Healed bones are not stronger than they were before a fracture.