ABSTRACT
Objective To investigate the effects from loads with different angles on morphological and biomechanical properties of trabecular bones in femoral head, so as to provide theoretical basis for studying biomechanical mechanism of necrosis and collapse of femoral head. Methods Ninety-four specimens of 12-month-old ovine trabecular bones in femoral head and forty-three specimens of human cadaver trabecular bones in femoral head were prepared. According to different angles between loading direction and principle compression direction, all the trabecular bones were divided into five groups by 10° interval (i.e. varus 10° and 0°, valgus 10°, 20° and 30°) to simulate the reduction condition under different Garden index after internal fixation of femoral neck fractures. Micro-CT scanning and calculation, compression failure test on ovine trabecular bones in femoral head and cyclic compression test on human cadaver trabecular bones in femoral head were performed to investigate morphological and mechanical indices, including BV/TV (bone volume vs. total volume), BS/BV (bone surface vs. bone volume), Tb.Th (thickness of trabecular bone), Tb.N (number of trabecular bone), Tb.Sp (trabecular separation), elastic modulus, ultimate strength, yield strength, initial secant modulus and number of cycles. Results When the angle between loading direction and principle compression direction of trabecular bones was 0°, BV/TV, Tb.Th, elastic modulus, ultimate strength, yield strength, initial secant modulus and number of cycles for trabecular bones were the maximum while BS/BV and Tb.N were the minimum, and all the formers presented decreasing tendency while BS/BV and Tb.N showed increasing tendency along with the angle increasing. ConclusionsAlong with the angle changes, the tendency of BV/TV and ultimate strength for 12-month-old ovine trabecular bones in femoral head displayed as the same as human trabecular bones in femoral head. Both the morphological and biomechanical properties of trabecular bones in femoral head will decrease when the angle between loading direction and principle compression direction of trabecular bones increases. The more the Garden index deviating from 160°, the more likely trabecular bones in femoral head to be damaged.
ABSTRACT
Objective To compare the differences in biomechanical properties of embalmed and PMMA femurs under axial loads, so as to provide a more reliable and unified femoral model for replacement. Methods Ten embalmed femurs and ten PMMA femurs were selected, and each femur was instrumented with 49 strain gauges totally on the medial and lateral side. The axial load was applied dynamically up to a maximum of 1.2 kN, and the strain of each strain gauge and load displacement curve were recorded. Results The strain distributions on two types of femur were similar, and the load displacement presented a linear relationship, but the vertical displacements under different loads were significantly different (P<0.05). The axial stiffness value of PMMA femur and embalmed femur were (259.84±24.63) and (600.40±78.56) N/mm, respectively, showing significant difference (P<0.01). The strain concentration parts at the proximal part of two femurs were the same, but the average strain value of the PMMA femur was significantly different from that of the embalmed femur (strain gauge No. 1~5: PMMA femur (-3 420.63±373.31) με, embalmed femur (-1 289.42±417.89) με; strain gauge No. 26~27: PMMA femur (1 748.67±193.98) με, embalmed femur (673.42±104.49) με; strain gauge No. 7~10: PMMA femur (-4 028.25±267.27) με, embalmed femurs (-1 139.01±288.83) με; strain gauge No. 30~36: PMMA femur (1 599.02±194.68) με, embalmed femurs (590.52±153.18) με, P<0.01). The strain concentration parts at the distal part of the two femurs were different. The medial and lateral parts of strain transformation between positive and negative of PMMA femurs were similar to embalmed femurs. The strain-load curves of strain gauge No. 2, 26, 6, 29, 8 and 33 indicated a linear relationship, but the strain value of the two femurs had significant differences (P<0.05). Conclusions The PMMA femur can replace the embalmed femur to a certain degree in biomechanical experiments on the upper part of femur. Due to the difficulty of obtaining fresh femurs, the PMMA femurs provide a more reliable and unified femoral model for replacement.