Injury - 2026-03-24 - Journal Article
Biomechanical analysis of protective plating configurations for interimplant femoral fracture prevention.
Llano L, Ziegler P, Mischler D, Baumann P, Zderic I, Varga P, Richards RG, Gueorguiev B, Höntzsch D, Stoffel K
Topics
Key Takeaway
Protective plating with screw overlap (short or long) beyond the innermost nail interlocking screws significantly reduces interimplant femoral strains versus no-overlap or no-plate configurations under 200 N axial load in osteoporotic synthetic bone.
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Summary
This study tested four protective plating configurations across a 40 mm interimplant gap between a proximal femoral nail and distal femoral nail in osteoporotic synthetic femora under 200 N axial compression, measuring surface strains via digital image correlation. No protective plating (Stage 1) produced significantly higher maximum strains than all plated configurations (p≤0.015); no-overlap plating (Stage 2) produced significantly higher strains than both short- and long-overlap configurations (p≤0.007), with no significant difference between short and long overlap (p>0.999). Peak strains consistently localized to the midpoint of the interimplant gap regardless of configuration.
Key Limitation
Synthetic osteoporotic bone models do not replicate the heterogeneous cortical thinning, endosteal scalloping, or viscoelastic behavior of cadaveric or in vivo osteoporotic femora, limiting direct translation of absolute strain values to clinical thresholds.
Original Abstract
INTRODUCTION
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.
MATERIALS AND METHODS
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.
RESULTS
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.
CONCLUSION
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.