How to heal a broken bone

Is it better to rest an injured limb completely or to begin using it as soon as possible?  According to a study by Robert Guldberg and his colleagues from the Georgia Institute of Technology, the answer is a little of both.  The best choice is to immobilize a broken bone for about four weeks, and then to start applying compressive forces to the injury.  At least, that’s the case for rats.

The scientists created gaps in rat limb bones and then seeded those gaps with a potent bone growth factor (human bone morphogenetic protein-2).  All the rats had plates screwed onto their injured legs to protect them from mechanical forces.  Some of those plates were rigid, whereas others had a release mechanism that allowed the bone to be compressed. 

Rats whose broken bones were immediately subjected to compressive loads did not heal very well.  The mechanical forces applied at the very beginning of the treatment prevented blood vessels from spreading into the injured area.  These rats suffered up to a 75% loss in bone formation.  However, the benefit of having the rigid plate only lasted for the first four weeks of healing.  After that time, the rats with the compressible plates began to fair better. 

 

Micro-computed angiography reconstructions of blood vessel formation in the area of the defect

Top: when it experienced no mechanical force for seven weeks

Bottom: when mechanical forces were exerted on the injury site beginning after four weeks for a duration of three weeks.

Credit: Joel Boerckel.

If this data applies to humans, it suggests that broken bones should only be immobilized for a few weeks after an injury.  And I certainly hope it does apply to humans since I’d hate to think of these rats going through these procedures for nothing.