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Prediction of femoral strength in a sideways fall configuration using QCT-based finite element analysis
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Abstracts / Bone 44 (2009) S68–S98
wk) from age 8 to 11 wks. Treatment was stopped from 11 to 17 wks of age and resumed from 17 to 20 wks of age. The treatment-naïve group (NAÏVE, N = 4) received hPTH injections (40 μg/kg/day, sc, 5×/ wk) from 17 to 20 wks of age only. Controls (VEH, N = 8) received vehicle injections. Outcomes included bone densitometry (PIXImus) in vivo and on excised femurs. Results: We observed a significantly blunted anabolic response to retreatment with hPTH. From 17 to 20 wks, total body BMC increased significantly more than VEH (5.3 ± 5.0%) in the NAÏVE (14.5 ± 5.9%, p = 0.02), but not in the RETREAT (7.4 ± 3.7%, p = 0.47) group (see Fig. 1). From 17 to 20 wks, total body BMC increased in PTH Naïve (+14.5 ±5.9%, vs. VEH (+5.3 ± 5.0%) (p = 0.02), but not in PTH Retreat (+7.4 ±3.7%) vs. VEH (NS). All groups exhibited significant BMC increases vs. baseline (p < 0.05), but PTH Naïve mice gained nearly twice as much total body BMC as PTH Retreat mice from 17 to 20 wks (p = 0.087). We then focused on the distal femur. Ex vivo, analysis of the distal 1/3 of the femur at 20 wks revealed 15–18% higher BMC in PTH Naïve vs. PTH Retreat (p = 0.05) or VEH (p = 0.02), but no difference between PTH Retreat and VEH.
impact loading rate in a sideways fall configuration. Mean femoral failure load was 3573 ± 1821 N, and ranged from 950 to 8915 N. Both total hip aBMD and FEA were strongly correlated with failure load in the full set (r2 = 0.72 and 0.78, respectively, Fig. 1). To assess the ability of aBMD to predict femoral strength, the sample was divided into a “training” set (n = 50) and “test” set (n = 26). The regression between total hip aBMD and femoral strength developed in the training set was used to predict femoral strength in the test set. The mean error in predicting failure load was ± 692 N (19.3% of the mean value). For FEA there was no training required, as the technique already provides a failure load prediction with no a priori knowledge. The mean error for FEA in the test set was ±702 N (19.6% of the mean value). In summary, these results show that with standardized imaging conditions and no soft tissue variation, femoral aBMD and QCT-based FEA are both strongly correlated with femoral strength in a sideways fall configuration. Further studies are needed to determine whether 3D-QCT based FEA will predict hip fracture risk better than DXA in clinical conditions where variability in subject positioning and body composition decreases the accuracy of aBMD measurements.
Conclusion: These results suggest the skeletal response to PTH therapy is blunted after interruption in treatment, for reasons that remain to be elucidated. This phenomenon has major implications for osteoporosis therapy. doi:10.1016/j.bone.2009.01.158 doi:10.1016/j.bone.2009.01.157
242 Prediction of femoral strength in a sideways fall configuration using QCT-based finite element analysis B.J. Robertsa, D. Kopperdahlb, E. Thralla, J.A. Mullera, T.M. Keavenyb,c, M.L. Bouxseina a Orthopedics, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA b ON Diagnostics, Berkeley, CA, USA c Department of Mechanical Engineering, UC Berkeley, Berkeley, CA, USA The gold standard for assessment of hip fracture risk is areal bone mineral density (aBMD, g/cm2) by DXA. However, recent studies have shown that up to half of those who fracture are not classified as osteoporotic by aBMD-based criteria. Thus, we sought to determine whether QCT-based Finite Element Analysis (FEA) is more strongly associated than aBMD with femoral strength. We obtained 76 human cadaveric femurs (50 female and 26 male, aged 74.2 ± 8.7 yrs, range 55 to 98 yrs), measured femoral aBMD by DXA, acquired QCT images at 1 mm slice thickness, and used them to perform voxel-based FEA (ON Diagnostics, Berkeley, CA). Femora were then tested to failure at
243 Measurement of cortical thickness in adolescents using HR-pQCT S. Braida,c, M. Burrowsa,c, D. Liua,c, J. Jokihaaraa,c, H.A. McKaya,b,c a Orthopaedics, UBC, Vancouver, British Columbia, Canada b Family Practice, UBC, Vancouver, British Columbia, Canada c Centre for Hip Health, VCHRI, Vancouver, British Columbia, Canada We have experienced an evolution over the last decade in medical imaging tools that safely and precisely evaluate the growing skeleton and – most recently – characterize the hierarchical nature of growing bone. High-resolution peripheral quantitative computed tomography (HR-pQCT; XtremeCT, Scanco Medical™) permits in vivo (110 slices; 9.02 mm) assessment of bone microstructure. It provides a direct assessment of cortical thickness (CTh, mm), an important component of bone strength. In the tibia, there is a rapid transition from highly trabecular bone and thin cortices at the metaphyses to wider cortices at the diaphyses. These characteristics are exaggerated in children where small trabeculae and thin cortices may present a measurement challenge. Therefore, our aims were, using HR-pQCT, to; 1) assess CTh in a defined region of interest (ROI) in the tibia and 2) use pQCTbased standards to determine whether the cortex could be assessed
Abstracts / Bone 44 (2009) S68–S98
wk) from age 8 to 11 wks. Treatment was stopped from 11 to 17 wks of age and resumed from 17 to 20 wks of age. The treatment-naïve group (NAÏVE, N = 4) received hPTH injections (40 μg/kg/day, sc, 5×/ wk) from 17 to 20 wks of age only. Controls (VEH, N = 8) received vehicle injections. Outcomes included bone densitometry (PIXImus) in vivo and on excised femurs. Results: We observed a significantly blunted anabolic response to retreatment with hPTH. From 17 to 20 wks, total body BMC increased significantly more than VEH (5.3 ± 5.0%) in the NAÏVE (14.5 ± 5.9%, p = 0.02), but not in the RETREAT (7.4 ± 3.7%, p = 0.47) group (see Fig. 1). From 17 to 20 wks, total body BMC increased in PTH Naïve (+14.5 ±5.9%, vs. VEH (+5.3 ± 5.0%) (p = 0.02), but not in PTH Retreat (+7.4 ±3.7%) vs. VEH (NS). All groups exhibited significant BMC increases vs. baseline (p < 0.05), but PTH Naïve mice gained nearly twice as much total body BMC as PTH Retreat mice from 17 to 20 wks (p = 0.087). We then focused on the distal femur. Ex vivo, analysis of the distal 1/3 of the femur at 20 wks revealed 15–18% higher BMC in PTH Naïve vs. PTH Retreat (p = 0.05) or VEH (p = 0.02), but no difference between PTH Retreat and VEH.
impact loading rate in a sideways fall configuration. Mean femoral failure load was 3573 ± 1821 N, and ranged from 950 to 8915 N. Both total hip aBMD and FEA were strongly correlated with failure load in the full set (r2 = 0.72 and 0.78, respectively, Fig. 1). To assess the ability of aBMD to predict femoral strength, the sample was divided into a “training” set (n = 50) and “test” set (n = 26). The regression between total hip aBMD and femoral strength developed in the training set was used to predict femoral strength in the test set. The mean error in predicting failure load was ± 692 N (19.3% of the mean value). For FEA there was no training required, as the technique already provides a failure load prediction with no a priori knowledge. The mean error for FEA in the test set was ±702 N (19.6% of the mean value). In summary, these results show that with standardized imaging conditions and no soft tissue variation, femoral aBMD and QCT-based FEA are both strongly correlated with femoral strength in a sideways fall configuration. Further studies are needed to determine whether 3D-QCT based FEA will predict hip fracture risk better than DXA in clinical conditions where variability in subject positioning and body composition decreases the accuracy of aBMD measurements.
Conclusion: These results suggest the skeletal response to PTH therapy is blunted after interruption in treatment, for reasons that remain to be elucidated. This phenomenon has major implications for osteoporosis therapy. doi:10.1016/j.bone.2009.01.158 doi:10.1016/j.bone.2009.01.157
242 Prediction of femoral strength in a sideways fall configuration using QCT-based finite element analysis B.J. Robertsa, D. Kopperdahlb, E. Thralla, J.A. Mullera, T.M. Keavenyb,c, M.L. Bouxseina a Orthopedics, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, USA b ON Diagnostics, Berkeley, CA, USA c Department of Mechanical Engineering, UC Berkeley, Berkeley, CA, USA The gold standard for assessment of hip fracture risk is areal bone mineral density (aBMD, g/cm2) by DXA. However, recent studies have shown that up to half of those who fracture are not classified as osteoporotic by aBMD-based criteria. Thus, we sought to determine whether QCT-based Finite Element Analysis (FEA) is more strongly associated than aBMD with femoral strength. We obtained 76 human cadaveric femurs (50 female and 26 male, aged 74.2 ± 8.7 yrs, range 55 to 98 yrs), measured femoral aBMD by DXA, acquired QCT images at 1 mm slice thickness, and used them to perform voxel-based FEA (ON Diagnostics, Berkeley, CA). Femora were then tested to failure at
243 Measurement of cortical thickness in adolescents using HR-pQCT S. Braida,c, M. Burrowsa,c, D. Liua,c, J. Jokihaaraa,c, H.A. McKaya,b,c a Orthopaedics, UBC, Vancouver, British Columbia, Canada b Family Practice, UBC, Vancouver, British Columbia, Canada c Centre for Hip Health, VCHRI, Vancouver, British Columbia, Canada We have experienced an evolution over the last decade in medical imaging tools that safely and precisely evaluate the growing skeleton and – most recently – characterize the hierarchical nature of growing bone. High-resolution peripheral quantitative computed tomography (HR-pQCT; XtremeCT, Scanco Medical™) permits in vivo (110 slices; 9.02 mm) assessment of bone microstructure. It provides a direct assessment of cortical thickness (CTh, mm), an important component of bone strength. In the tibia, there is a rapid transition from highly trabecular bone and thin cortices at the metaphyses to wider cortices at the diaphyses. These characteristics are exaggerated in children where small trabeculae and thin cortices may present a measurement challenge. Therefore, our aims were, using HR-pQCT, to; 1) assess CTh in a defined region of interest (ROI) in the tibia and 2) use pQCTbased standards to determine whether the cortex could be assessed