Objective: To determine whether a position screw will maintain the interfragmentary compression force obtained by a reduction clamp across an anatomically reduced cortical bone fracture and determine whether this compressive force is equivalent to that generated by a lag screw (LS).
Methods: Oblique fractures were created in 6 composite cortical bone models. Interfragmentary compression was measured using force sensors within the fracture after reduction with a clamp. A position screw was then placed perpendicular to the fracture, and force measurements were repeated with both the clamp and the screw. Finally, the clamp was removed, and force measurements were taken with the screw only to measure maintenance of initial compression. After these measurements, the screw was removed, and the near fragment was overdrilled to allow LS placement by technique. Compression force measurements were repeated for clamp only, clamp + screw, and screw only.
Results: The mean force of clamp alone across all 12 trials was 139.77 N. Application of an LS increased the compression across the fracture (P = 0.01) which was unchanged when the clamp was removed. The position screw had the opposite effect, reducing compression, and the removal of the clamp further reduced the compression (P = 0.013).
Conclusions: A reduction clamp will initially compress a fracture to an average of 139 N. An LS will significantly increase this interfragmentary compression. A position screw will not maintain the compression created by the clamp and in fact will significantly decrease interfragmentary compression.