A biomechanical study comparing cortical onlay allograft struts and plates in the treatment of periprosthetic femoral fractures

Background: Periprosthetic femoral fractures with well-fixed femoral components can be difficult to manage and internal fixation is usually necessary. This study was designed to determine the effect of cable plate, strut allograft and combined plate and strut allograft fixations of periprosthetic femoral fractures. Methods: A transverse fracture at the level of the tip of the femoral stem was simulated in six cadaveric femurs. The fracture was fixed with a plate–strut graft construct with and without proximal screws, a plate only construct with and without proximal screws and with both anterior and lateral struts grafts of 12 cm or 20 cm in length. The intact femur and the six constructs were tested using anteroposterior and axial loads to simulate the forces at the hip during gait. The interfragmentary motions were measured with an optoelectronic camera system. Findings: The highest median interfragmentary translations were observed with the plate only construct without proximal screws. No significant differences in median translations were found between the combined plate–strut and the strut-graft alone constructs. Median interfragmentary rotations were largest with the plate only construct and lowest with the plate–strut constructs. Interpretation: The best fracture fixation was achieved with the combined plate and strut graft constructs particularly in combination with the two unicortical screws above the fracture. The plate only constructs may not provide sufficient fixation stability in rotation for the simulated transverse fracture. The within-construct interfragmentary motions were not significantly different except for the plate only constructs. This suggests that the fixation construct type is the determining factor of interfragmentary motion.