How wide of a distal metaphyseal femoral fracture gap is a high risk of varus collapse and fixation failure? A finite element study.

BACKGROUND

Severe metaphyseal comminution and sizable bone defect of the distal femur are high risks of fixation failure. To date, no exact magnitude of comminution and bone loss is determined as an indication for augmentation of fixation construct. The present study aimed to investigate the influence of metaphyseal gap width, working length, and screw distribution on the stability of the fixation construct.

METHODS

A finite element model of a fractured femur with 0-80 mm metaphyseal gap width stabilized by an 11-hole distal femur locking compression plate (LCP-DF) was generated. The different working length and screw distribution were created by three different screw configurations: 9-10-11 (long working length, cluster screw), 8-10-11, and 7-9-11 (short working length, spreading screw). Physiological loading conditions were applied to evaluate biomechanical performance including equivalent von Mises (EQV) stress, bone stress, and fracture strain.

RESULTS

The EQV stress increased accordingly to a metaphyseal gap width of 0-20 mm. The EQV stress values were at the same levels for 30-mm metaphyseal gap width and higher, particularly in screw configuration 9-10-11. Screw configuration 7-9-11 produced the lowest elastic strain. A 0-mm metaphyseal gap width presented the lowest bone stress. Bone stress values were in a similar magnitude across a 10-80 mm metaphyseal gap.

CONCLUSION

The 30-mm and wider metaphyseal gap width with a long working length presented a risk of varus collapse and fixation failure. Short working length with spreading screw provided low EQV stress, low bone stress, and high fracture stability.