In 1999, Krettek et al. introduced the concept of placing screws around an intramedullary nail (so-called Poller screws)1,2. These screws were used in association with interlocking nailing of tibial fractures with either proximal or distal fragments to facilitate alignment and to prevent late loss of alignment. Krettek et al. recommended placing one screw proximally and one distally on the concave side of the displacement. These screws were thought to work by narrowing the medullary canal in the metaphysis to provide a tight mechanical fit for the intramedullary nail. Similarly, Biewener et al. employed the sequential placement of Kirschner wires to guide an intramedullary nail with a good central position into a distal short fragment3. This procedure was called the “pallisade method.”

To clarify the mechanical effect of such screws and to provide a better understanding of their placement, a mechanical model was designed.

### Description of the Model

The model has long and short rectangular Lucite plates that represent the diaphysis and metaphysis of a long bone, respectively (Fig. 1). Aluminum frames are fixed to these Lucite plates to represent the cortex. The plates have matching convex surfaces at the metaphyseal-diaphyseal junction so that they can rotate on one another to simulate angular misalignment. A rubber band can be used to connect the short and long cortical segments in order to model unbalanced muscle forces, which cause axial malalignment. Three different inserts can be used to fill the end of the short segment. These inserts provide either a central entry portal, an eccentric entry portal, or a central zone into which the “nail” can be embedded. The nail is an opaque plastic bar that can be introduced into the medullary cavity from either the metaphyseal or the diaphyseal portion of the model. Holes on both sides of the nail …