Impact of end-screw configuration on peri-implant fracture risk in distal femoral plating.

Abstract

Locked plating of distal femoral fractures is associated with a risk of secondary peri-implant fractures predominantly resulting from stress concentrations around the proximal plate end. This study aimed to investigate whether the strength of healed femoral bone-locking compression plate constructs can be increased by modifying the end screw type to minimize the risks of peri-implant femoral fractures. Twenty-four artificial femurs were fixed with Distal Femur Locking Compression Plates (DF-LCP) in four different end screw configurations (n = 6): bicortical nominal locking screw (bLS), bicortical conventional screw oriented perpendicular to the plate (CS), unicortical nominal locking screw (uLS), and 15° proximally angulated bicortical conventional screw (aCS). To represent a healed post-fracture situation, intact femurs without a fracture gap were plated. All specimens underwent quasi-static loading to failure, while bone surface strain was measured. All failure modes featured peri-implant bone fractures at end screw level. Failure load was 238.3 N ± 19.3 N for bLS, 257.4 N ± 23.8 N for CS, 271.0 N ± 43.0 N for uLS, and 289.8 N ± 26.8 N for aCS, being significantly higher for aCS versus bLS (p = 0.032), with no further significant differences between the configurations (p ≥ 0.250). Strain measurements revealed significant advantages for aCS. Under the tested conditions, using aCS was related to increased failure load and associated with a more favorable peri-implant strain pattern compared with bLS, suggesting a potentially reduced mechanical predisposition to peri-implant fracture. These findings support further evaluation of angulated bicortical end screws, particularly in osteoporotic bone models.