Table 5.

Types of ex-vivo mechanical tests for the evaluation of the biomechanical properties of explanted bone specimens.

Mechanical Test	Schematic Representation		Advantages	Disadvantages	Observations
Tensile test		Specimen is usually a round bar with a reduced middle region and a length-to-diameter ratio of 5:1.	Allows for relatively easy assessment of the strain of bone (by using strain gauges).	1. Usually requires large specimens; 2. Some bending might be applied to the specimen, leading to measurement errors; 3. Requires the specimen to be machined; 4. Only one component of load is applied—incomplete evaluation of the mechanical properties.	1. Easier to perform for cortical bone than cancellous since cancellous bone is difficult to clamp; 2. Tensile load is calculated by dividing the applied force divided by the cross-sectional area in the midsection of the specimen.
Compression test		Specimen is usually a cube or cylinder having a length-to-diameter ratio of 2:1.	1. Usually requires small specimens; 2. Fabrication of the specimens is easier than for tensile tests.	1. The presence of “end effects”1 often leads to errors; 2. Strain is very difficult to measure; 3. Only one component of load is applied—incomplete evaluation of the mechanical properties.	Reducing the size of the specimen increases the risk of “end-effects” 1.
Bending test		Can be performed in a 3- or 4-point bending set-up.	Both components of load are applied—tensile stresses are present on one side of the specimen and compressive stresses on the opposite side.	1. Highly influenced by the size and shape of the specimen—defects throughout the specimen may lead to non-accurate results; 2. A 3-point bending produces several transverse shear stresses in the middle of the specimen while 4-point bending model applies almost pure bending stresses.	1. Since bone is weaker in tension than compression, failure usually occurs on the tensile side of the bone; 2. Positioning of the specimen should be very precise, since each loading point has to be equal to obtain accurate results.
Torsion test		Specimen has a reduced central portion to ensure that the failure occurs in the middle part.	1. Measures the biomechanical properties of bone under shear stress; 2. When the specimen is twisted, shear stresses vary from zero at the center of the specimen to the maximum value at the surface; 3. Both compression and tension are present.	1. Requires the specimen to be machined; 2. Practical issues may occur (i.e., clamping the sample to the testing device).	Testing strongly influenced by the shape of the specimen.

¹ “End effects” are measurement errors that originate from the damage incurred at the end surfaces of machined specimens.