Biomechanical analysis of protective plating configurations for interimplant femoral fracture prevention.

Abstract

Interimplant femoral fractures (IFFs), occurring between or adjacent to implants such as hip prostheses and intramedullary nails, pose complex treatment challenges, particularly in osteoporotic patients. Biomechanical research highlights the need to protect the interimplant region from high strains, however, optimal configurations for plate fixation remain unclear. This study analyzes strains in the interimplant region under various protective plate configurations. Twelve synthetic proximal femora, mimicking osteoporotic bone, were instrumented with a proximal femoral nail (PFN) and a distal femoral nail (DFN) creating a 40 mm interimplant gap. Four implant configurations were tested: no protective plating (Stage 1), screws placed inside the innermost nail interlocking screws (no overlapping, Stage 2), screws placed outside and close to the innermost nail interlocking screws (short overlapping, Stage 3), and screws placed outside and far from the innermost nail interlocking screws (long overlapping, Stage 4). A non-destructive axial compressive load (200 N) was applied, and bone surface strains were measured beneath the plate using digital image correlation. Stage 1 (no protective plating) exhibited significantly higher maximum strains versus Stages 2-4 (p ≤ 0.015). Stage 2 (no overlapping) showed maximum strains being significantly higher compared to both short and long overlapping (p ≤ 0.007), without further significant difference between the latter two (p > 0.999). Similar trends were observed for strains at point-specific locations defined intermittently between the innermost nail interlocking screws. The highest point-specific strains were located in the middle of the interimplant region. From a biomechanical perspective, the application of a protective plate fixation of the interimplant region significantly reduces strains, with long and short overlapping providing optimal mechanical protection. Adequate protection with plates should be prioritized to mitigate the risk of interimplant fractures.