The influence of "kickstand" screws on the mechanical performance of a lateral distal femoral plate : a finite element analysis.

Abstract

Aims: Lateral locked plating of distal femoral fractures is widely reported, yet there remains a 9% to 19% incidence of mechanical failure. Obliquely directed "kickstand screws", from the metaphyseal portion of a plate toward far-sided articular subchondral bone, have been shown to improve construct stiffness. This study explores the impact of kickstand screws in a finite element analysis bone defect model, comparing plate and screw maximum stress and maximum locking screw forces either with or without the addition of kickstand screws.

Methods: A finite element analysis model of a lateral based femoral plate and fracture gap simulation was created, with material and construct data parameters regarding bone material, implant, and composite model identified. The addition of the upper, lower, or both kickstand screws in an anatomical precontoured lateral distal femoral plate were selected as the variables compared against the absence of kickstand screws. Screw and plate principal stresses (MPa) and locking screw mechanism force (N) were measured.

Results: The addition of the upper kickstand screw or both kickstand screws led to an approximate 40% reduction of stress in the metaphyseal hole closest to the fracture. The addition of the lower, upper, and both kickstand screws led to a 23%, 32%, and 34% reduction of maximum stress in the metaphyseal screws, respectively. The addition of the lower kickstand screw led to a 19% reduction, while the upper or both kickstand screws led to a 23% reduction of maximum force experienced by the locking mechanism.

Conclusion: The addition of kickstand screws improves the mechanical performance of the construct, with reduced stresses experienced by the plate and metaphyseal screws. Furthermore, the maximum forces on the locking screw mechanism were shown to be significantly reduced, providing a protective effect to the polyaxial locking mechanism of the metaphyseal screw.