Scientific Presentation at the BOA / IOA Combined Meeting 2011
14th September 2011.
D Gibson, C Keogh, S Morris.
A biomechanical study comparing the dynamic hip screw with an X-Bolt
in an unstable intertrochanteric fracture model of the proximal femur.
ABSTRACT:
Introduction: Lag screw cut-out following fixation of unstable intertrochanteric fractures in osteoporotic bone remains an unsolved challenge. A novel new device is the X-Bolt which is an expanding type bolt that may offer superior fixation in osteoporotic bone compared to the standard DHS screw type device.
Aims: The aim of this study was to test if there was a difference in cut-out using the X-Bolt implant compared with the standard DHS system.
Methods: Specimens of low density surrogate bone (5pcf) were inserted into a simplified biomechanical fracture model and had either an X-Bolt or DHS implant inserted. There were eight samples in each group. The fracture model was tested with an incremental cyclical loading programme in a Material Test System. Displacement, cycle count and force exerted were continuously recorded until cut-out of the implant.
Results: All of the specimens failed by varus collapse with superior cut-out and resulted in an automatic stop of the MTS. Specimens with the X-Bolt implant inserted lasted longer on cyclical count and withstood a greater force at cut-out compared with DHS specimens. The mean number of cycles to cutout in the DHS specimens was 4345 and in specimens with the X-Bolt inserted was 6898. The mean force at which cutout occurred in the DHS group was 1.025kN and in specimens with the X-Bolt inserted was 1.275kN. A statistically significant difference was observed with a P-value of 0.005 and a power of 87.2% with respect to cycle count and a P-value of 0.008 and power 84.8% with respect to force exerted at failure when comparing between the two groups.
Conclusion: This study shows that the X-Bolt device demonstrated superior cut-out resistance and withstood greater loads compared to the DHS in low density surrogate bone in an unstable fracture model under cyclical axial loading.