My son had a limb-lengthening surgery about three months ago. He was back in school fairly quickly despite having a metal cage wrapped around his leg. But he's active and would like to get this off sooner than later. Is it really necessary to keep this contraption on much longer?

In a limb-lengthening operation, the short bone is cut and the two ends are distracted or pulled apart. The special external fixator device (cage) that you mentioned is used to distract the bone. The patient returns to the surgeon's office at regular intervals and has the bone distracted many times.

Over time, as much as three inches can be added to the short leg. This does take time. Often the device is left in place for as long as 10 months. An average of 200 days (seven months) is more common.

Removing the fixator too soon can result in bone fracture and further leg deformity. Studies report a range of five to 40 per cent of fractures after fixator removal. Most of the fractures occur without any trauma or known cause. The bone just hasn't regenerated enough to withstand the forces of everyday movement.

It's possible that the fixator could be removed sooner. But caution is advised without objective measurements of bone stiffness or bone mineral density to guide the surgeon. Researchers are actively trying to determine reliable and accurate guidelines to use when making this decision. For now, time, X-ray results, and ultrasound give us a best-guess estimate of healing.