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Specialized metallic bone plates are used to stabilize various types of bone fractures which occur in the upper and lower extremities. A knowledge of the relative bending strength and stiffness of bone plates is desirable to evaluate the effect of different materials and designs on clinical performance. Bending stiffness in the elastic region is primarily a function of the modulus of elasticity of the material and plate dimensions. Adequate bending strength is important to resist permanent deformation associated with single-cycle overload stress. Proper contouring of bone plates in the operating room is related to plate design.
ISO 9585, “Implants for Surgery — Method for Testing Bending Strength and Stiffness of Bone Plates,” describes a static four-point bend test for bone plates. Testing factors such as bone plate length, cylindrical roller dimensions, and flatness deviations are specified in the ISO test method. Plate placement on the bending rollers and plate orientation must also be controlled for consistent bend test results.
Correct interpretation of the load-deflection curve is required to accurately determine proof load, mean deflection, equivalent bending stiffness, and bending strength. Calculations based on established formulas are presented for typical test configurations.
Bend test results are compiled for implant-quality 316L stainless steel and unalloyed titanium, cloverleaf and T-plates. A modified test arrangement is described for the evaluation of 1.5 mm and 2.0 mm titanium mini-fragment plates.
proof load, bending strength, equivalent bending stiffness
Mechanical Test Engineer, SYNTHES (USA), Paoli, PA
Materials Development Director, SYNTHES (USA), Paoli, PA.