Biomechanical evaluation of periprosthetic refractures following distal femur locking plate fixation

Distal femur fractures proximal to total knee femoral component constitutes the most prevalent type of periprosthetic fracture, and plate fixation treatment is associated with a 7.7% incidence of refracture proximal to the plate. The primary objective of this study was to compare proximal fixation techniques of a periprosthetic distal femur fracture plate in an osteoporotic bone model. The secondary objective was to determine the subsequent periprosthetic plate fracture pattern and/or complexity associated with each proximal plate fixation configuration.

A segmental defect was created in 21 synthetic osteoporotic adult femurs 6 cm proximal to the distal femur and all specimens were stabilised with a 246 mm locking femur plate. Fixation in the most proximal hole was varied by use of either a cerclage cable, unicortical locking screw, or a bicortical locking screw. Specimens were tested to failure in simultaneous eccentric compression and torsion.

Proximal cerclage fixation demonstrated higher mean maximum axial force at failure (4142.67±178.71 N, p<0.001), stiffness (443.8±61.64 N/mm), and maximum torque (20.9±0.93 N m, p<0.001). Unicortical and bicortical screw refractures occurred at the screw, cerclage wire refractures occurred at the first proximal screw distal to the cerclage.

In periprosthetic distal femur fracture locking plate fixation, proximal hole stabilization with a cerclage wire tolerates significantly higher failure forces while distributing forces distal to the area within the plate fixation. Cerclage wiring may be an option in distal femur periprosthetic fractures to alleviate stress risers in vulnerable bone.