Biomechanical Evaluation of Osteoporotic Proximal Periprosthetic Femur Fractures With Proximal Bicortical Fixation and Allograft Struts.

OBJECTIVES: To evaluate the strength of proximal bicortical fixation using a novel osteoporotic synthetic bone model of Vancouver B1 periprosthetic proximal periprosthetic femur fractures (PFFs) and to assess the influence of strut allograft augmentation with regard to allowing early assisted weight bearing. The secondary aim was to evaluate whether the strut position, either medial or anterior, influenced the strength of the construct.

METHODS: Thirty synthetic osteoporotic femurs were implanted with cemented stems. A segmental defect made distal to the stem simulated a fracture and was repaired with a stainless steel locking compression plate and 2 stainless steel proximal locking attachment plates. Specimens were then divided into 3 groups: no-strut, medial strut, and anterior strut. Cadaveric femoral struts were wired to the specimens. Cyclic axial compression simulated assisted weight bearing and was followed by loading to failure.

RESULTS: Medial struts required higher failure load than no-strut (P = 0.008) and more energy to failure than anterior (P = 0.018) or no-strut (P < 0.001). The higher load to failure, however, would not be advantageous in clinical practice because estimates for assisted weight bearing after fractures in average-weight patients are well below these failure loads. Furthermore, all specimens tolerated cyclical loading. All failures occurred distal to the plate originating at the last screw hole.

CONCLUSIONS: Failure loads for all groups were above what would be expected for low-demand activities of assisted weight bearing. Therefore, proximal bicortical fixation should allow for early, assisted weight bearing without allograft strut augmentation even with lower density bone.