Measuring Young's modulus of single trabeculae in cancellous bone using a two-point bending test.

BACKROUND: Surgical treatment of proximal humeral fractures poses a major challenge, especially in osteoporotic bone. At present, there appears to exist neither a suitable model for research to optimize the osteosynthesis processes nor are the structural data available which are required for developing such a model. Therefore, the aim of this study is to determine the microscopic morphology and Young's modulus of cancellous bone from human humeral heads considering osteoporotic changes. METHODS: Cylindrical samples were taken from ten fresh-frozen human humeral heads and structural analysis was done with µCT. Ten rod-like trabeculae were prepared from five of the humeral heads each which were measured and tested mechanically. For this purpose, the trabeculae were fixed on a slide and rotated axially under a stereo microscope. The sample cross-section and the depending moment of inertia were extracted from the image data. The samples were then loaded in a 2-point bending test and Young's moduli of the samples were determined. RESULTS: It could be shown that with increasing age of the donor, ossified portion of the cancellous bone decreased (p < 0.05). The average degree of mineralization of the bone was 1.24 (±0.06) g/mm3, which decreased with increasing age (p < 0.05). The determined Young's modulus averaged 1.33 (±1.76) GPa. INTERPRETATION: The verified structural parameter showed osteoporotic changes in the examined bone. This study for the first time determined Young's modulus of single trabeculae of cancellous bone of osteoporotically altered human humeral heads. Implementing the non-destructive sample measurement before exposure resulted in a methodical improvement.

Determination of E-modulus of cancellous bone derived from human humeri and validation of plotted single trabeculae: Development of a standardized humerus bone model.

Background: Evaluation of the mechanical behavior of the microstructure of cancellous bone seems important for the understanding of the mechanical behavior of bone. Prevention and treatment of fragility fractures due to osteoporosis is a major challenge according to ageing population. A bone model might help to assess fracture risk. Measurement of single trabeculae of bone should give further information compared with bone densitometry alone. This study measures the mechanical properties of single cancellous trabeculae derived from human proximal humerus. Methods: 34 single trabeculae dissected from human humeral heads were measured and evaluated mechanically. Trabeculae were fixed on microscope slides and geometrical data were reported during axial rotation of the specimens to measure the transverse section using computer aided design (CAD). The samples were subjected to a two-point bending test and were loaded with a measure-stamp at a defined distance. Force and deflection were measured by high-resolution sensors. The E-modulus was then calculated in combination with finite elements method simulation (FEM), using the previously obtained CAD-Data. Results: The average E-modulus from 34 valid measurements of human humeral trabeculae was 1678 MPa with a range from 829 to 3396 MPa, which is consistent with existing literature. The planned additional validation of the measurement method using manufactured three-dimensional synthetic trabeculae with known mechanical properties showed an average elastic modulus of single trabeculae of 51.5 MPa, being two dimensions lower than the value reported in the datasheet of the plastic. Conclusion: This newly developed, time and cost-efficient procedure allows the measurement of E-modulus in single trabeculae. Measurement of mechanic parameters of single trabeculae might give insights on mechanic behavior of bone and be relevant for the research of systemic bone diseases, complementing the existing data on bone-mineral-density. Further examination of single trabeculae of human cancellous bone should give an insight on the mechanical behavior of bone also considering systemic bone diseases.