Evolution of the concept of an extensible nail accommodating to normal longitudinal bone growth: clinical considerations and implications.

Based on animal experiments, we observe that the central portion of an epiphysis can be subjected to acute trauma in a low order of its cross-sectional area without interfering with growth. Moreover, the presence of a metallic device of small diameter placed across the center of the distal femoral epiphysis of a growing dog does not interfere with growth. A metal pin with a T-shaped end can be placed across the distal femoral epiphysis of a growing dog with the T-shaped end fixed in the epiphysis without interfering with growth. As growth occurs, migration of the spin or elongation of the femur beyong the pin does not occur. On the contrary, the T-shaped device, because of fixation of the end of the T, is passively carried along with the epiphysis as the femur elongates with growth. Based on the above experiments, an extensible fixative device was developed which would elongate with the distracting force of growth. The nail responded to these forces, elongating with femoral growth and did not retard growth. Microscopic analysis of the nail tracts across the epiphyseal plates showed no tendency to premature closure of the epiphyseal line. The tracts formed by the nails were lined with fibrous tissue; the remainder of the epiphysis showed a normal histologic structue.