A biomechanical comparison of fibular strut and femoral head allograft for augmented locking plate fixation in three-part proximal humerus fractures

Background: It is not clear whether cortical fibular allografts or cancellous femoral allografts provide similar stability for augmentation of locking plate fixation of proximal humerus fractures. Therefore, this study aimed to assess and compare biomechanical properties of augmented locking plate fixation with 1) a cortical fibular allograft and 2) a cancellous femoral allograft. Methods: Twenty-two fresh frozen humeri were randomly allocated to undergo unstable three-part fracture creation, locking plate fixation, and augmentation with cortical fibular or cancellous femoral allografts. All constructs were tested with cyclic loading (5 N to 532.5 N) for 1000 cycles at 1 Hz. Subsequently, constructs were loaded to 1700 N. Loss of humeral head height (HHH), ultimate failure loads, mode of failure, and stiffness were assessed. Results: Twenty humeri were included in the analysis. No failure occurred during cyclic loading. During load-to-failure testing, four (40.0%) fibula-augmented constructs and six (60.0%) femoral-augmented constructs failed. During cyclic loading, median loss of HHH was 2.00 (interquartile range [IQR], 1.12-3.50) for fibular grafts and 2.75 (IQR, 2.00-3.00) femoral grafts (P = .40). Median loss of HHH during failure tests was 9.50 (IQR, 7.88-15.50) for fibular grafts and 9.50 (IQR, 8.50-10.90) for femoral grafts (P = .68). The stiffness for fibular grafts was 174 (IQR, 106-186) and 157 for femoral grafts (IQR, 134-192) (P = .97). Conclusion: There is no significant difference in biomechanical stability between cortical fibular allograft augmentation and cancellous hip allograft augmentation for locking plate fixation in proximal humerus fractures. Both techniques may equally prevent loss of reduction and early screw protrusion. Cancellous femoral allografts may yield advantages considering costs, availability, and future revision surgery with arthroplasty when compared to cortical fibular allografts.