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  1. 1. References Developing an Osteoporotic Bone Model Using Canine Specimens Rebecca Cunningham, Benjamin Parkhurst, Mustapha Zailah BME 3504, Group #9, B term, 2010 Biomedical Engineering Department, Worcester Polytechnic Institute, Worcester, MA Abstract Osteoporosis affects approximately ten million Americans most of which are female (National Osteoporosis Foundation , 2010). Osteoporosis weakens bones making them prone to fracture. Surgeons have difficulty stabilizing and treating fractured osteoporotic bone. In order to help evaluate the effectiveness of surgical procedures such as the use of plates and screws, an osteoporotic model is needed to assess mechanical properties of osteoporotic bone in comparison with normal bone . The tibias and femurs from eight canine legs from four small dogs were used in this study. Decalcifying agents formic acid and ammonium formate were used in half of the canine bones to induce the osteoporosis (Kiviranta, 1980). Corresponding bones from the same dog served as controls. A three point bending test using Instron Model 5544 were used to break all of the bone samples. Data collected using the Bluehill software was used to determine the ultimate tensile strength (UTS), stiffness (E), maximum force, and maximum moment of the samples. Comparisons of the corresponding treated and untreated bone samples indicates that osteoporosis was induced in the treated samples. The average UTS of treated samples 21.8 % lower than the untreated samples. Methods 1. National Osteoporosis Foundation (2010). About Osteoporosis:Having a Bone Density Test. Retrieved from http://www.nof.org/aboutosteoporosis/detectingosteoporosis/bmdtest 2. Dickenson, W. Hutton, J. Stott (1981). The Mechanical Properties of Bone in Osteoporosis. Polytechnic of Central London and the RAF Institute of Aviation Medicine, Farnborough. Vol. 63-B, No. 296-8. 3. Kiviranta I, Tammi M, Lappalainen R, Kuusela T, Helminen HJ (1980). The rate of calcium extraction during EDTA decalcification from thin bone slices as assessed with atomic absorption spectrophotometry. Histochemistry 68:119127. 4. J. L.Kuhn et al (1989). The Limitations of Canine Trabecular Bone as a Model for Human: A Biomechanical Study. J. Biomechanics. Vol. 22, No. 2, pp. 95 107. Conclusions and Future Research Acknowledgements Special thanks to Dr. Jack Hawkes for providing us with dog legs from the Cummings School of Veterinary Medicine at Tufts University anatomy lab Calculated mechanical properties were vastly different between the two groups Avg. UTS was reduced by 21.8% in treated samples Stiffness was determined using a linear fit of the linear region of the F vs. D curves Linear fits all had R values between 0.96-0.999 at a 95% confidence level Average Stiffness was 5.47 GPa in untreated samples and 8.68GPa in treated samples Results with Figures and Tables Canine cadaver legs were obtained via Tufts Anatomy Lab Canine bone has a similar density to that of human bone (Kuhn, 1989) Left and right tibias and femurs were extracted from the two hind legs of four small dogs A 1L aqueous solution with 70.0 g formic acid and 17.0g liquid ammonium formate was combined over low heat until the formic acid was completely dissolved 2 ml HCL used to lower the pH from 6 to 4.5 Ammonium formate used in place of potassium formate as a buffer One tibia and one femur from each dog was treated in the formic acid solution; the other bones served as a control Treated bones were placed in the formic acid solution for 61.5 hours to induce osteoporosis Treated bones were washed with 6.15% NaOCl Clorox bleach solution to remove excess soft tissue Three point bending test used to break all samples (figure 1) Instron applied a force to the center of the bone until failure Diameter of each bone and length of grip distance were measured with a caliper Bending test broke all samples; controls were tested first, osteoporotic were tested later Assumptions: Cross-section of bone assumed to be circular and hollow (wall thickness measured after samples were broken), see figure 2 Bone assumed to be isotropic, homogeneous, and linearly elastic Calculations: Max Moment: (F*L)/4: F=Max Force (N), L = distance between grips Moment of Inertia: I=*(R0 4 -Ri 4 )/4, where Ro is outer radius, Ri is inner radius of the bone UTS: UTS= (M *R0 )/I, where M is the max moment and I is the moment of inertia Stiffness: E=(slope of F vs D linear region)*L3 /(48*I) Table 1: Control Bone Results Figure 1: Bending Test Similar to Equipment Used Image Source: http://www.mc.vanderbilt.edu/root/vumc.php? site=CenterForBoneBiology&doc=20412 Figure 2: Geometry of the cross-section of the bones Research has shown that the ultimate tensile strength of osteoporotic bone is about 81% than that of healthy bone (Dickenson et al., 1981). According to our data, the UTS of the treated bones was about 78% of the UTS of the untreated bones. Based on this data it is acceptable to assume that the osteoporotic model has been met. Stiffness was the only variable to increase upon inducing osteoporosis. The fact that the Max Force and the Max Moment were significantly reduced indicates that this procedure can be used to induce osteoporosis. Limitations/Future Research Density was not measured to further indicate osteoporosis A possible improvement to this procedure would be to drill a hole in the ends of both the control and experimental samples so that the bone marrow could be removed and any decalcifying solutions could reach a larger surface area Canine samples were different sizes and from different breeds, figure 5 shows the largest femur used. This sample was from an unknown breed labeled as Black Dog Variability was reduced by matching samples from the same dog Figure 3: Force vs. Displacement of Control Samples Figure 4: Force vs. Displacement of Treated Samples Sample Max Force (N) I (mm^4) Max Moment (N-mm) Ultimate Tensile Strength (UTS) (Mpa) E (Stiffness) (Gpa) Black Dog Left Tibia 98.6 133 1730 47.0 22.8 Black Dog Right Femur 490 83.7 8570 330 23.8 Dachshund #1 Left Femur 481 138 4810 127 5.62 Dachshund #1 Left Tibia 746 128 7460 209 6.13 Dachshund #2 Left Femur 707 279 7070 111 2.74 Dachshund #2 Left Tibia 507 132 5070 139 6.55 Min Pin Left Femur 254 275 3170 50.1 0.096 Min Pin Left Tibia 169 222 2540 46.9 1.73 Mean 432 174 5050 133 8.68 Standard Deviation 220 13 2300 91 8.7 Sample Max Force (N) I (mm^4) Max Moment (N-mm) Ultimate Tensile Strength (UTS) (Mpa) E (Stiffness) (Gpa) Black Dog Left Tibia 528 190 11900 250 18.0 Black Dog Right Femur 616 172 10800 245 12.9 Dachshund #1 Left Femur 1170 129 8790 246 3.39 Dachshund #1 Left Tibia 840 244 6300 111 1.28 Dachshund #2 Left Femur 1270 159 11900 284 4.59 Dachshund #2 Left Tibia 222 436 10200 118 2.27 Min Pin Left Femur 316 227 2780 53.2 0.182 Min Pin Left Tibia 749 369 3960 52.2 1.21 Mean 748 241 8330 170 5.47 Standard Deviation 360 100 3300 90 6.0 Table 2: Treated Bone Results -20 -15 -10 -5 0 -1000 -800 -600 -400 -200 Displacement (mm) Force(N) Black Dog Left Femur Black Dog Right Tibia Dachshund #1 Right Femur Dachshund #1 Right Tibia Dachshund #2 Right Femur Dachshund #2 Right Tibia Min Pin Right Femur Min Pin Right Tibia -25 -20 -15 -10 -5 0 -700 -600 -500 -400 -300 -200 -100 Displacement (mm) Force(N) Black Dog Right Femur Dachshund #1 Left Femur Dachshund #1 Left Tibia Dachshund #2 Left Femur Dachshund #2 Left Tibia Min Pin Left Femur Black Dog Left Tibia Min Pin Left Tibia Ro Ri Figure 5: Measuring of The Right Black Dog Femur Sample (treated)