Non-invasive assessment of failure torque in rat bones with simulated lytic lesions using computed tomography based structural rigidity analysis (original) (raw)
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Bone, 2014
There is an urgent need to improve the prediction of fracture risk for cancer patients with bone metastases. Pathological fractures that result from these tumors frequently occur in the femur. It is extremely difficult to determine the fracture risk even for experienced physicians. Although evolving, fracture risk assessment is still based on inaccurate predictors estimated from previous retrospective studies. As a result, many patients are surgically over-treated, whereas other patients may fracture their bones against expectations. We mechanically tested ten pairs of human cadaveric femurs to failure, where one of each pair had an artificial defect simulating typical metastatic lesions. Prior to testing, finite element (FE) models were generated and computed tomography rigidity analysis (CTRA) was performed to obtain axial and bending rigidity measurements. We compared the two techniques on their capacity to assess femoral failure load by using linear regression techniques, Student's t-tests, the Bland-Altman methodology and Kendall rank correlation coefficients. The simulated FE failure loads and CTRA predictions showed good correlation with values obtained from the experimental mechanical testing. Kendall rank correlation coefficients between the FE rankings and the CTRA rankings showed moderate to good correlations. No significant differences in prediction accuracy were found between the two methods. Non-invasive fracture risk assessment techniques currently developed both correlated well with actual failure loads in mechanical testing suggesting that both methods could be further developed into a tool that can be used in clinical practice. The results in this study showed slight differences between the methods, yet validation in prospective patient studies should confirm these preliminary findings.
Journal of Orthopaedic Research, 2004
Pathologic fracture is a significant risk for patients afflicted with metastatic or benign skeletal tumors. The quandary for physicians who treat these patients is that after making the diagnosis they must try to predict the load bearing capacity of the involved bone and the fracture risk from images seen in radiological examinations. Since bone fails at a relatively constant strain independent of density we demonstrate that using a mechanics of materials approach that the cross-sectional structural properties of the bone most affected by the lytic defect governs the load bearing capacity of the entire bone.
Journal of Biomechanics, 2010
Mechanical testing has been regarded as the gold standard to investigate the effects of pathologies on the structure-function properties of the skeleton. With recent advances in computing power of personal computers, virtual alternatives to mechanical testing are gaining acceptance and use. We have previously introduced such a technique called structural rigidity analysis to assess mechanical strength of skeletal tissue with defects. The application of this technique is predicated upon the use of relationships defining the strength of bone as a function of its density for a given loading mode. We are to apply this technique in rat models to assess their compressive skeletal response subjected to a host of biological and pharmaceutical stimulations. Therefore, the aim of this study is to derive a relationship expressing axial compressive mechanical properties of rat cortical and cancellous bone as a function of equivalent bone mineral density, bone volume fraction or apparent density over a range of normal and pathologic bones.
Dual-Energy X-Ray Absorptiometry in Predicting Mechanical Characteristics of Rat Femur
Bone, 1998
Dual-energy X-ray absorptiometry (DXA), geometrical measurements, and mechanical testing of the rat femoral shaft and neck were performed on both femora of 51 Sprague-Dawley rats to: (i) determine the reproducibility of the DXA, geometrical, and biomechanical measurements of rat femora; (ii) determine linear and power-law (y ؍ ax b ) associations between the site-specific bone mineral variables and the actual mechanical characteristics of the given sites; (iii) develop, if sufficiently strong associations were found, appropriate prediction equations for the breaking load (F) and flexural rigidity (EI) of the femoral shaft and neck (only for F); and (iv) validate these equations in terms of accuracy of prediction. In the majority of the DXA measurements, the repeatability of the measurements was good, the CV rms varying between 1.2% and 3.9% in the bone mineral density (BMD) measurements and between 1.6% and 13.8% in the bone mineral content (BMC) measurements. DXA also proved accurate in length measurements of the rat femur (measurement error <1%). The manual (digimatic caliper-obtained) geometrical measurements of the rat femora were equally precise, the CV rms values varying between 0.2% and 5.0%. The repeatability of the biomechanical testings of these femora varied between 5.0% and 14.7%. Virtually all of the power-law and linear models explained more than 80% (at best 97%) of the variation in the F of the femoral shaft and neck, and the EI of the femoral shaft. Despite the high grouplevel correlations between the DXA-based predictions of bone strength and the actual breaking loads of the rat femora, and good precision of DXA, the ability of any DXA-based estimate to predict accurately the actual biomechanical characteristics of an individual bone remained relatively poor. In extreme cases, the prediction error could be tens of percent. Despite this we feel that bone strength-estimating equations can be used in the group-level analyses of experimental and clinical studies. Care must be taken, however, when choosing the most appropriate prediction method for a particular study. (Bone 22:551-558; 1998)
European Journal of Medical Research, 2018
Objectives: Rat fracture models are extensively used to characterize normal and pathological bone healing. Despite, systematic research on inter-and intra-individual differences of common rat bones examined is surprisingly not available. Thus, we studied the biomechanical behaviour and radiological characteristics of the humerus, the tibia and the femur of the male Wistar rat-all of which are potentially available in the experimental situation-to identify useful or detrimental biomechanical properties of each bone and to facilitate sample size calculations. Methods: 40 paired femura, tibiae and humeri of male Wistar rats (10-38 weeks, weight between 240 and 720 g) were analysed by DXA, pQCT scan and three-point-bending. Bearing and loading bars of the biomechanical setup were adapted percentually to the bone's length. Subgroups of light (skeletal immature) rats under 400 g (N = 11, 22 specimens of each bone) and heavy (mature) rats over 400 g (N = 9, 18 specimens of each bone) were formed and evaluated separately. Results: Radiologically, neither significant differences between left and right bones, nor a specific side preference was evident. Mean side differences of the BMC were relatively small (1-3% measured by DXA and 2.5-5% by pQCT). Over all, bone mineral content (BMC) assessed by DXA and pQCT (TOT CNT, CORT CNT) showed high correlations between each other (BMC vs. TOT and CORT CNT: R 2 = 0.94-0.99). The load-displacement diagram showed a typical, reproducible curve for each type of bone. Tibiae were the longest bones (mean 41.8 ± 4.12 mm) followed by femurs (mean 38.9 ± 4.12 mm) and humeri (mean 29.88 ± 3.33 mm). Failure loads and stiffness ranged from 175.4 ± 45.23 N / 315.6 ± 63.00 N/mm for the femurs, 124.6 ± 41.13 N / 260.5 ± 59.97 N/mm for the humeri to 117.1 ± 3 3.94 N / 143.8 ± 36.99 N/mm for the tibiae. Smallest interindividual differences were observed in failure loads of the femurs (CV% 8.6) and tibiae (CV% 10.7) of heavy animals, light animals showed good consistency in failure loads of the humeri (CV% 7.7). Most consistent results of both sides (left vs. right) in failure loads were provided by the femurs of light animals (mean difference 4.0 ± 2.8%); concerning stiffness, humeri of heavy animals were most consistent (mean difference of 6.2 ± 5%). In general, the failure loads showed strong correlations to the BMC (R 2 = 0.85-0.88) whereas stiffness correlated only moderate, except for the humerus (BMC vs. stiffness: R 2 = 0.79). Discussion: Altogether, the rat's femur of mature specimens showed the most accurate and consistent radiological and biomechanical results. In synopsis with the common experimental use enabling comparison among different
Bone & joint research, 2012
This study aims to assess the correlation of CT-based structural rigidity analysis with mechanically determined axial rigidity in normal and metabolically diseased rat bone. A total of 30 rats were divided equally into normal, ovariectomized, and partially nephrectomized groups. Cortical and trabecular bone segments from each animal underwent micro-CT to assess their average and minimum axial rigidities using structural rigidity analysis. Following imaging, all specimens were subjected to uniaxial compression and assessment of mechanically-derived axial rigidity. The average structural rigidity-based axial rigidity was well correlated with the average mechanically-derived axial rigidity results (R(2) = 0.74). This correlation improved significantly (p < 0.0001) when the CT-based Structural Rigidity Analysis (CTRA) minimum axial rigidity was correlated to the mechanically-derived minimum axial rigidity results (R(2) = 0.84). Tests of slopes in the mixed model regression analysis i...
Orthopedic Reviews, 2013
Knowledge of local bone quality is essential for surgeons to determine operation techniques. A device for intraoperative measurement of local bone quality has been developed by the AO-Research Foundation (DensiProbe®). We used this device to experimentally measure peak breakaway torque of trabecular bone in the proximal femur and correlated this with local bone mineral density (BMD) and failure load. Bone mineral density of 160 cadaver femurs was measured by ex situ dual-energy X-ray absorptiometry. The failure load of all femurs was analyzed by side-impact analysis. Femur fractures were fixed and mechanical peak torque was measured with the DensiProbe® device. Correlation was calculated whereas correlation coefficient and significance was calculated by Fisher’s Z-transformation. Moreover, linear regression analysis was carried out. The unpaired Student’s t-test was used to assess the significance of differences. The Ward triangle region had the lowest BMD with 0.511 g/cm2 (±0.17 g/...
2015
Original Research Paper Received 25 December 2014 Accepted 24 February 2015 Available Online 04 April 2015 Quantitative computed tomography (QCT) -based finite element analysis is commonly accepted approach for prediction of mechanical behavior of bones. The objective of this research was to suggest linear criterion in order to accelerate and increase the precision of predicting failure load in femoral bone. Accordingly, ten fresh frozen femora were QCT scanned and prepared for use in this study. The specimens were loaded under eight different orientations. Finite element model for these samples were generated from QCT images, and related mechanical properties were calculated for each single voxel based on the value of density. In addition, the models were analyzed by linear finite element method. Risk factor, that is defined as the strain energy density divided to yield strain energy for each element was used for calculations of failure load. These values were sorted for particular...