Dataset Information

Computed tomography porosity and spherical indentation for determining cortical bone millimetre-scale mechanical properties.

ABSTRACT: The cortex of the femoral neck is a key structural element of the human body, yet there is not a reliable metric for predicting the mechanical properties of the bone in this critical region. This study explored the use of a range of non-destructive metrics to measure femoral neck cortical bone stiffness at the millimetre length scale. A range of testing methods and imaging techniques were assessed for their ability to measure or predict the mechanical properties of cortical bone samples obtained from the femoral neck of hip replacement patients. Techniques that can potentially be applied in vivo to measure bone stiffness, including computed tomography (CT), bulk wave ultrasound (BWUS) and indentation, were compared against in vitro techniques, including compression testing, density measurements and resonant ultrasound spectroscopy. Porosity, as measured by micro-CT, correlated with femoral neck cortical bone's elastic modulus and ultimate compressive strength at the millimetre length scale. Large-tip spherical indentation also correlated with bone mechanical properties at this length scale but to a lesser extent. As the elastic mechanical properties of cortical bone correlated with porosity, we would recommend further development of technologies that can safely measure cortical porosity in vivo.

SUBMITTER: Boughton OR

PROVIDER: S-EPMC6520408 | biostudies-literature | 2019 May

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

Computed tomography porosity and spherical indentation for determining cortical bone millimetre-scale mechanical properties.

Boughton Oliver R OR Ma Shaocheng S Cai Xiran X Yan Liye L Peralta Laura L Laugier Pascal P Marrow James J Giuliani Finn F Hansen Ulrich U Abel Richard L RL Grimal Quentin Q Cobb Justin P JP

Scientific reports 20190515 1

The cortex of the femoral neck is a key structural element of the human body, yet there is not a reliable metric for predicting the mechanical properties of the bone in this critical region. This study explored the use of a range of non-destructive metrics to measure femoral neck cortical bone stiffness at the millimetre length scale. A range of testing methods and imaging techniques were assessed for their ability to measure or predict the mechanical properties of cortical bone samples obtained ...[more]

PMID: 31092837

Similar Datasets

Project description:ObjectivesBone material properties are a major determinant of bone health in older age, both in terms of fracture risk and implant fixation, in orthopaedics and dentistry. Bone is an anisotropic and hierarchical material so its measured material properties depend upon the scale of metric used. The scale used should reflect the clinical problem, whether it is fracture risk, a whole bone problem, or implant stability, at the millimetre-scale. Indentation, an engineering technique involving pressing a hard-tipped material into another material with a known force, may be able to assess bone stiffness at the millimetre-scale (the apparent elastic modulus). We aimed to investigate whether spherical-tip indentation could reliably measure the apparent elastic modulus of human cortical bone.Materials and methodsCortical bone samples were retrieved from the femoral necks of nineteen patients undergoing total hip replacement surgery (10 females, 9 males, mean age: 69 years). The samples underwent indentation using a 1.5 mm diameter, ruby, spherical indenter tip, with sixty indentations per patient sample, across six locations on the bone surfaces, with ten repeated indentations at each of the six locations. The samples then underwent mechanical compression testing. The repeatability of indentation measurements of elastic modulus was assessed using the co-efficient of repeatability and the correlation between the bone elastic modulus measured by indentation and compression testing was analysed by least-squares regression.ResultsIn total, 1140 indentations in total were performed. Indentation was found to be repeatable for indentations performed at the same locations on the bone samples with a mean co-efficient of repeatability of 0.4 GigaPascals (GPa), confidence interval (C.I): 0.33-0.42 GPa. There was variation in the indentation modulus results between different locations on the bone samples (mean co-efficient of repeatability: 3.1 GPa, C.I: 2.2-3.90 GPa). No clear correlation was observed between indentation and compression values of bone elastic modulus (r = 0.33, p = 0.17). The mean apparent elastic modulus obtained by spherical indentation was 9.9 GPa, the standard deviation for each indent cycle was 0.11 GPa, and the standard deviation between locations on the same sample was 1.01 GPa. The mean compression apparent elastic modulus was 4.42 GPa, standard deviation 1.02 GPa.DiscussionSpherical-tip indentation was found to be a repeatable test for measuring the elastic modulus of human cortical bone, demonstrated by a low co-efficient of repeatability in this study. It could not, however, reliably predict cortical bone elastic modulus determined by platens compression testing in this study. This may be due to indentation only probing mechanical properties at the micro-scale while platens compression testing assesses millimetre length-scale properties. Improvements to the testing technique, including the use of a larger diameter spherical indenter tip, may improve the measurement of bone stiffness at the millimetre scale and should be investigated further.

Project description:Reference point indentation (RPI) is a microindentation technique involving 20 cycles of loading in "force-control" that can directly assess a patient׳s bone tissue properties. Even though preliminary clinical studies indicate a capability for fracture discrimination, little is known about what mechanical behavior the various RPI properties characterize and how these properties relate to traditional mechanical properties of bone. To address this, the present study investigated the sensitivity of RPI properties to anatomical location and tissue organization as well as examined to what extent RPI measurements explain the intrinsic mechanical properties of human cortical bone. Multiple indents with a target force of 10N were done in 2 orthogonal directions (longitudinal and transverse) per quadrant (anterior, medial, posterior, and lateral) of the femoral mid-shaft acquired from 26 donors (25-101 years old). Additional RPI measurements were acquired for 3 orthogonal directions (medial only). Independent of age, most RPI properties did not vary among these locations, but they did exhibit transverse isotropy such that resistance to indentation is greater in the longitudinal (axial) direction than in the transverse direction (radial or circumferential). Next, beam specimens (~2mm×5mm×40mm) were extracted from the medial cortex of femoral mid-shafts, acquired from 34 donors (21-99 years old). After monotonically loading the specimens in three-point bending to failure, RPI properties were acquired from an adjacent region outside the span. Indent direction was orthogonal to the bending axis. A significant inverse relationship was found between resistance to indentation and the apparent-level mechanical properties. Indentation distance increase (IDI) and a linear combination of IDI and the loading slope, averaged over cycles 3 through 20, provided the best explanation of the variance in ultimate stress (r(2)=0.25, p=0.003) and toughness (r(2)=0.35, p=0.004), respectively. With a transverse isotropic behavior akin to tissue hardness and modulus as determined by micro- and nano-indentation and a significant association with toughness, RPI properties are likely influenced by both elastic and plastic behavior of bone tissue.

Project description:The diagnosis of fracture risk relies almost solely on quantifying bone mass, yet bone strength is governed by factors at multiple scales including composition and structure that contribute to fracture resistance. Furthermore, aging and conditions such as diabetes mellitus alter fracture incidence independently of bone mass. Therefore, it is critical to incorporate other factors that contribute to bone strength in order to improve diagnostic specificity of fracture risk. We examined the correlation between femoral neck fracture strength in aging female cadavers and areal bone mineral density, along with other clinically accessible measures of bone quality including whole-bone cortical porosity (Ct.Po), bone material mechanical behavior measured by reference point indentation (RPI), and accumulation of advanced glycation end-products (AGEs). All measurements were found to be significant predictors of femoral neck fracture strength, with areal bone mineral density (aBMD) being the single strongest correlate (aBMD: r = 0.755, p < 0.001; Ct.Po: r = -0.500, p < 0.001; RPI: r = -0.478, p < 0.001; AGEs: r = -0.336, p = 0.016). RPI-derived measurements were not correlated with tissue mineral density or local cortical porosity as confirmed by micro-computed tomography (μCT). Multiple reverse stepwise regression revealed that the inclusion of aBMD and any other factor significantly improve the prediction of bone strength over univariate predictions. Combining bone assays at multiple scales such as aBMD with tibial Ct.Po (r = 0.835; p < 0.001), tibial difference in indentation depth between the first and 20th cycle (IDI) (r = 0.883; p < 0.001), or tibial AGEs (r = 0.822; p < 0.001) significantly improves the prediction of femoral neck strength over any factor alone, suggesting that this personalized approach could greatly enhance bone strength and fracture risk assessment with the potential to guide clinical management strategies for at-risk populations.

Dataset Information

Computed tomography porosity and spherical indentation for determining cortical bone millimetre-scale mechanical properties.

Publications

Computed tomography porosity and spherical indentation for determining cortical bone millimetre-scale mechanical properties.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets