There are times when it would be helpful to know how well healed a bone is in a growing child. For example, when the bone is strong enough, hardware used to support the leg during healing can be removed. This situation arises after surgery for bone fracture, limb lengthening, or joint fusion.
In this study, the method of measuring bone stiffness in adults is applied to children. The idea was to see if it is an acceptable way to measure the strength of the healing bone. It would be helpful if a safety baseline could be established. Having a safe value when external fixation could be removed would help surgeons progress treatment of these children.
A small number of children (11) were involved in this study. All were in good health and having surgery to lengthen one leg. Boys and girls between the ages of five to 16 were included. A device called an Orthometer was used to measure bone stiffness.
Measurements were taken while the child was under general anesthesia after pins had been inserted to hold the bone in place. A special tool called a goniometer was used to measure the change in angle of the bone. Stiffness was recorded and bone angulation was measured in the anteroposterior (AP) direction (front to back). The same measurements were taken in the mediolateral (ML) direction (side to side).
All measurements were entered into a microcomputer that calculated the stiffness values. The results showed that all AP measurements were directly linked with ML stiffness of the bone. If the AP stiffness increased, the ML stiffness increased, too. And the triangular-shaped tibia (lower leg bone) was always stronger than the circular-shaped and more flexible femur.
AP stiffness was also correlated with height. In other words, stiffness increased with greater heighth. There was a wide range of differences among the children based on height and weight. Age did not appear to be a factor.
This was the first study to look at leg bone stiffness in children using an Orthometer. The authors point out that different results might be found in arm bones. So the baseline values obtained are to be considered preliminary.
More studies will be needed to validate these Orthometer measurements during the healing phase of children. The goal is to find a minimal value or range of safe Orthometer readings that will guide surgeons in the removal of pins, plates, cages, and other surgical hardware.