The Cut Out Phenomenon: An Experimental Analysis of the Migration Behaviour of Lag Screws for Fixation of Pertrochanteric Fractures

Abstract

The cut out phenomenon of lag screws after internal fixation of intertrochanteric fractures remains an unsolved pathophysiological and biomechanical problem. The purpose of the current study was to analyse the migration behaviour of different hip screw implants in a standardised experimental setting using a specific testing machine and bone substitute material to mimic different bone densities. Migration of lag screws was significantly influenced by bone density and could significantly be improved by a central position of the lag screw in the femoral head adjacent to its cortical bone and a wide collodiaphyseal angle. Larger outside diameter lag screws showed a significantly higher resistance to migration than those with a smaller outside diameter. Self cutting or non-self cutting threads did not show any significant difference. In a double screw system different positions of the screws showed different cut out resistance.

Key words

Cut out - intertrochanteric fractures of femur - lag screw

References

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