Comparative dynamic evaluation of the sliding/characteristics of the Gamma nail: a biomechanical analysis

This study was directed at establishing the influence of dynamic loading situations on the sliding characteristics of the Gamma locking nail (Howmedica). It was postulated that the changing regions of load contact area that occur within the sliding mechanism during flexion and extension would favourably modify the jamming behaviour observed under static test conditions. The forces required to initiate sliding of the lag screw in the intramedullary device were investigated under a range of conditions representing clinical situations. The optimum sliding performance of the Gamma nail was shown to occur during test conditions of dynamic loading, when the rate of application of the load was rapid and the cyclic angle of flexion was greatest. The size and weight of the patient also influence the sliding characteristics, as a shorter lag screw length protruding from the barrel and a reduced vertical static load (body weight) yielded a lower axial sliding force. The results under dynamic loading conditions suggest that static testing of sliding hip screws does not accurately represent their clinical performance.