Reducing femoral peri-implant fracture risk through optimized plate length and screw configuration - a biomechanical study.

backgroundLocked plating of femur fractures is associated with secondary peri-implant fractures which may be a result of stress concentrations at the proximal plate end region. The aim of this study was to investigate whether the strength of healed femoral bone-locking-compression-plate constructs can be increased by modifying the screw configurations and plate length to minimize the risks of peri-implant femur fractures.

methodsThe detached shaft of a variable angle condylar locking compression plate (VA-LCP Condylar Plate; Johnson & Johnson MedTech) was fixed to the proximal two-third of twenty-four intact artificial femurs in four different configurations (n = 6) distinguished by either using a short plate with cortical or locking screws whereby the most proximal screw was inserted in the femoral shaft 50 mm below the lesser trochanter, or using a long plate with either cortical or locking screws whereby the most proximal screw was positioned in the femoral neck. Simulating a situation after fracture healing, constructs were cyclically tested under progressively increased loading until catastrophic failure.

resultsLong plates fixed with a cortical screws demonstrated the highest failure load (1091 N ± 142 N) which was significantly higher compared to long plates fixed with locking screws (888 N ± 80 N), short plates fixed with cortical screws (471 N ± 42 N), and short plates fixed with locking screws (450 N ± 19 N). In addition, whereas the locking screw construct with a long plate was associated with a significantly higher failure load compared to both short plate constructs, there were no significant differences between the latter two. The failure modes were predominantly characterized by neck screw pull-out in both long plate constructs and peri-implant bone fractures at the most proximal screw in both constructs with short plates. None of the specimens exhibited a femoral neck fracture.

conclusionThe findings of this study performed on synthetic bones indicate that from a biomechanical perspective long plates that extend into the femoral neck sustained higher failure loads compared to short plates. In addition, long plates fixed with a cortical neck screw further enhanced the construct strength and reduced the risk of peri-implant fractures compared to the use of a locking neck screw. Therefore, this study supports the use of long locking plates combined with use of cortical neck screws, particularly in high-risk patients, such as those with severe osteoporosis.