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Locked Plate Fixation of Proximal Humerus Fractures Using Cannulated Subchondral Support Pegs

Background In severely osteoporotic proximal humerus fractures, the biomechanics of fixed-angle fracture fixation with locked smooth pegs may be improved by using polymethyl methacrylate (PMMA) augmentation. Commercially available smooth pegs were modified (added a central cannula and two distal side ports) to accommodate bone cement injection around the pegs. The failure strength and stiffness of proximal humerus fracture fixation with modified pegs and PMMA augmentation was evaluated. Methods Nineteen fresh-frozen cadaveric humeri were fixated with a locked plate using: (i) smooth pegs (seven specimens), (ii) threaded pegs (six specimens) or (iii) modified smooth pegs with PMMA augmentation (six specimens). The osteotomized humeri constructs were subjected to an axial compressive load to failure at loading rate of 5 mm/minute. The maximum failure load and slope for each specimen was calculated. Results There was no difference (p > 0.31) between the failure strength of constructs containing smooth or threaded pegs. However, the mean failure strength and stiffness of modified smooth pegs with PMMA augmentation was higher than the constructs containing either the smooth or threaded pegs. Conclusions The results obtained in the present study show that the use of PMMA augmentation along with smooth pegs may benefit humerus fracture patients with severe osteoporosis.