Augmentation of a Locking Plate System Using Bioactive Bone Cement—Experiment in a Proximal Humeral Fracture Model

INTRODUCTION: The purpose of this study was to test whether local filling of a novel strontium-containing hydroxyapatite (Sr-HA) bone cement can augment the fixation of a locking plate system in a cadaveric proximal humeral facture model. MATERIALS AND METHODS: Twelve pairs of formalin-treated cadaveric humeri were used. One side in each pair was for cemented group, while the other side was for the control group. The bone mineral density (BMD) of the samples was tested. A 3-part facture model was created and then reduced and fixed by a locking plate system. In the cemented group, the most proximal 4 screw holes were filled with 0.5 mL bone cement. In the control group, the screw holes were not filled by cement. Locking screws were inserted in a standard manner before the cement hardened. X-ray was taken before all the specimens being subjected to mechanical study, in which 6 pairs were used for axial loading (varus bending) test, while other 6 pairs were used for axial rotational test. RESULTS: There is no difference in BMD between the cemented side and the control side. The X-ray shows that the implant is in position. Cement filling was noted in the most proximal 4 screws in the cemented group. Better mechanical outcome was seen in the cemented groups, in terms of less maximal displacement per cycle and higher failure point and stiffness in varus bending test. However, no difference was found between the cemented group and the control group in the axial rotation test. DISCUSSION: In similarity with the previous studies, our results showed better mechanical results in the cemented group. However, due to the limitations (e.g. sample size, fracture model, testing protocol, etc), we still cannot directly extrapolate current mechanical results to clinical practice at the present moment. Furthermore, it is still unknown whether better primary outcome may lead to better long-term results, even though the local release of strontium may enhance the local bone formation. CONCLUSION: The local filling of Sr-HA bone cement augments the fixation of the locking plate system in current proximal humeral fracture model.