During interlocking nailing the displaced butterfly fragments can be left in situ or reduced by opening the fracture site. The purpose of this study is to investigate the fate of the displaced comminuted butterfly fragments when left unreduced and factors that influences fracture union in comminuted femoral fracture after closed interlocking nailing.

Out of 95 closed interlocking nailings done for fractured femur from July 1990 to July 1993, 43 femoral fractures that had comminuted fragments larger than 1 cm were followed for more than 18 months postoperatively, The correlations between the size of the comminuted fragments, its distance from the femoral shaft, the angulation of the fragment, the gap of the main fracture sites and bone union were analyzed.

The distance between the fragment and the femoral shaft and angulation spontaneously decreased gradually, even the fractures having inverted fragments were united uneventfully, and the union rate of the fractures with gap less than 3 mm was higher than those with gap greater than 3 mm.

The displaced fragment need not be reduced by open method and minimizing the fracture gap is recommended in increasing the union rate.