Abstract
Introduction
Locking plates can provide greater stability than conventional plates; however, reports revealed that fractures had a high incidence of failure without medial column support; the mechanical support of medial column could play a significant role in humeral fractures. Recent studies have demonstrated the importance of intramedullary strut in proximal humeral fracture fixation, the relationship to mechanical stability and supporting position of the strut remain unclear. The purpose of this study was to evaluate the influence of position of the intramedullary strut on the stability of proximal humeral fractures using a locking plate.
Materials and methods
Ten humeral sawbone (Synbone) and locked plates (Synthes, cloverleaf plate), with and without augmented intramedullary strut (five in each group) for proximal humerus fractures, were tested using material testing machine to validate the finite element model. A 10 mm osteotomy was performed at surgical neck and a strut graft (10 cm in length) was inserted into the fracture region to lift the head superiorly. Each specimen was statically tested at a rate of 5 mm/min until failure. To build the finite element (FE) model, 64-slices CT images were converted to create a 3D solid model. The material properties of screws and plates were modeled as isotropic and linear elastic, with an elastic modulus of 110 GPa, (Poisson's ratio, n=0.3). The Young's moduli of cortical and cancellous bones were 17 GPa and 500 MPa (n=0.4), respectively. Three alter shifting toward far cortex by 1, 2, and 3 mm in humeral canal were installed in the simulating model.
Results and discussion
The test result showed stiffness for only locked plate was 149.2±21.3 N/mm; and the plating combined with an intramedullary strut was 336.5±50.4 N/mm. On average, the stiffness was increased by 2.2 times in the augmented fixation relative to the only locking plate fixation. The finite element analytical results showed stiffness of 162 N/mm for fixation without strut, and 372 N/mm for those with strut augmentation. The stiffness between experiment and FE analysis agreed in 8.6% for the only locking plate case; and agreed in 10.5% for the case fixed with intramedullary strut. FE analysis showed the stability of construct increased 7%, 11% and 20% as the strut shift by 1, 2, and 3 mm, respectively. Gardner (2007) reported the importance of mechanical support at the medial region for maintenance of reduction when proximal humerus fracture treated with locking plates.
Conclusion
The intramedullary strut may provide superior stability than the only locking plate fixation. The FE model provides a useful implement to find the optimal configuration of plate fixation.
Acknowledgements
All authors thank the funding support from National Science Council (NSC 102-2628-B-650-001) and E-Da Hospital (EDPJ1020027).
