Heterogeneous Glycation of Cancellous Bone and Its Association with Bone Quality and Fragility

Non-enzymatic glycation (NEG) and enzymatic biochemical processes create crosslinks that modify the extracellular matrix (ECM) and affect the turnover of bone tissue. Because NEG affects turnover and turnover at the local level affects microarchitecture and formation and removal of microdamage, we hypothesized that NEG in cancellous bone is heterogeneous and accounts partly for the contribution of microarchitecture and microdamage on bone fragility. Human trabecular bone cores from 23 donors were subjected to compression tests. Mechanically tested cores as well as an additional 19 cores were stained with lead-uranyl acetate and imaged to determine microarchitecture and measure microdamage. Post-yield mechanical properties were measured and damaged trabeculae were extracted from a subset of specimens and characterized for the morphology of induced microdamage. Tested specimens and extracted trabeculae were quantified for enzymatic and non-enzymatic crosslink content using a colorimetric assay and Ultra-high Performance Liquid Chromatography (UPLC). Results show that an increase in enzymatic crosslinks was beneficial for bone where they were associated with increased toughness and decreased microdamage. Conversely, bone with increased NEG required less strain to reach failure and were less tough. NEG heterogeneously modified trabecular microarchitecture where high amounts of NEG crosslinks were found in trabecular rods and with the mechanically deleterious form of microdamage (linear microcracks). The extent of NEG in tibial cancellous bone was the dominant predictor of bone fragility and was associated with changes in microarchitecture and microdamage

Repair, regenerative and supportive therapies of the annulus fibrosus: achievements and challenges

Lumbar discectomy is a very effective therapy for neurological decompression in patients suffering from sciatica due to hernia nuclei pulposus. However, high recurrence rates and persisting post-operative low back pain in these patients require serious attention. In the past decade, tissue engineering strategies have been developed mainly targeted to the regeneration of the nucleus pulposus (NP) of the intervertebral disc. Accompanying techniques that deal with the damaged annulus fibrous are now increasingly recognised as mandatory in order to prevent re-herniation to increase the potential of NP repair and to confine NP replacement therapies. In the current review, the requirements, achievements and challenges in this quickly emerging field of research are discussed

Trabecular bone modeling and subcapital femoral fracture

Fragility fractures, including neck of femur fractures, result from reductions in the amount, quality and architecture of bone. The aim of this study was to compare the cancellous bone structure, and static indices of bone turnover, in female patients who had sustained fragility fracture at the femoral neck, with age-matched females without fragility fracture. Bone samples were taken from the intertrochanteric region of the proximal femur of female patients undergoing hip arthroplasty surgery for a subcapital fragility fracture of the femoral neck (#NOF) or from age-matched female control individuals at routine autopsy. The histomorphometric data, which were normally distributed, indicated no difference between the mean values for any of the structural parameters in control and fracture samples. In particular, the BV/TV values were not different and did not change significantly with age in these cohorts of individuals aged >65 years. The static indices of bone turnover, eroded surface (ES/BS) and osteoid surface (OS/BS), were positively correlated with age in the >65-year-old control group (p65-year-old controls compared with a group of younger females aged <65 years, suggesting an increase in bone formation in older females in the proximal femur after 65 years of age. When the data were further interrogated, a reduction in the percentage osteoid surface to eroded surface quotient (OS/ES) was found for the fracture group compared with the age-matched control group. These data indicate that perturbations in bone formation and/or resorption surface are potentially important in producing bone in the proximal femur with increased propensity to fracture. These data also support the concept that trabecular bone modeling may be a factor influencing bone strength in addition to bone mass.H. Tsangari, J.S. Kuliwaba, N.L. Fazzalar

Effect of fatigue-induced microdamage on the fracture resistance of human cortical bone

Codrington J.D, Fazzalari N.L and Kotousov A.Ghttp://www.anzbms.org.au/asm/asm2010

Cancellous bone microdamage in the proximal femur: Influence of age and osteoarthritis on damage morphology and regional distribution

This study describes the in vivo distribution of cancellous bone microdamage in the proximal femur of an autopsy control sample. In addition, in vivo microdamage in the region medial to the greater trochanter of the proximal femur is compared between patients with severe osteoarthritis and controls. Taken at autopsy, the control group comprised normal right proximal femora that were then cut in the coronal plane with an Exakt saw (n = 12; aged 20-83 years). Cancellous bone samples were taken from the subchondral principal compressive region, the medial principal compressive region, and medial to the greater trochanter. A cancellous bone core biopsy was taken of the region medial to the greater trochanter (of the proximal femur) from patients with primary osteoarthritis undergoing total hip replacement surgery (n = 33; aged 37-85 years). Samples were embedded in resin, and in vivo microdamage identified in 70-microm-thick sections using the basic fuchsin en bloc staining technique. Microdamage was similar in all proximal femur sites in controls, except in the subchondral principal compressive region, where a significantly smaller crack length (microm) was identified (p < 0.05). In the region medial to the greater trochanter, osteoarthritic vs. control group comparisons showed that the crack density (#/mm(2)) and crack surface density (mm/mm(2)) were not significantly different, but crack length was significantly less (p < 0.03) and damage volume fraction was significantly increased for osteoarthritics (p < 0.005). The osteoarthritic and control data for crack density, and the osteoarthritic data for damage volume fraction, showed a nonlinear increase with age. Furthermore, crack length was not dependent on damage volume fraction or age for either the osteoarthritic or control group. This study identified differences in microdamage between osteoarthritic and autopsy control cases. We hypothesize that these results are consistent with the reported bone material property differences for osteoarthritis. In addition, the relatively uniform distribution of microdamage in the control group suggests that the principal components of the femoral cancellous bone network are equally exposed to deformations resulting in microdamage. Further study into the factors that influence the accumulation and skeletal distribution of microdamage is fundamental to understanding skeletal health

The effect of hydration on the stiffness of intervertebral discs in an ovine model

ObjectiveTo determine the hydration-over-time behaviour of ovine intervertebral discs and intact joints in a saline bath at body temperature and the effect this has on their stiffness compared to air at ambient temperature.DesignThe hydration-over-time behaviour and stiffness of the ovine functional spinal unit and disc were quantified.BackgroundThe fluid content of an intervertebral disc is not constant but varies with external load and load history. The stiffness of ovine functional spinal units in a hydrated environment and how this compares to testing in air have not been quantified.MethodsIntervertebral discs and functional spinal units were weighed and soaked in a saline water bath at 37 degrees C and reweighed each hour for 6 h. They were then allowed to stand in air at room temperature while the time to return to initial weight was recorded. Functional spinal units were randomly assigned to two groups. Axial compression, flexion, extension, lateral bending and axial torsion tests were performed on both the intact functional spinal unit and isolated disc. Group 1 was tested in air then in a saline water bath at 37 degrees C with the testing order reversed for Group 2.ResultsHydration of the disc reached a plateau after an average 3-4 h of soaking with the largest increase seen in the first hour. Four hours, standing in air at room temperature, was required to return specimens to their initial weight. The functional spinal unit stiffness was significantly lower for those specimens tested in the bath compared to air.ConclusionsOvine intervertebral discs show similar hydration-over-time behaviour when compared to human discs. Stiffnesses in different modes of loading were significantly different when tested in a hydrated environment compared with the standard method of testing in air.RelevanceIt has been shown that there are biomechanical and biochemical similarities between sheep and human intervertebral discs. Despite these similarities, no studies have looked at how ovine intervertebral discs behave over time in a hydrated environment. In humans, hydration levels are an important aspect of intervertebral disc degeneration. There is also a relationship between decreased hydration levels and increased stiffness. This study demonstrates the similarities between human and ovine hydration-over-time behaviour. The importance of intervertebral disc hydration and its effects on stiffness under different modes of loading were also demonstrated and have not been previously shown using the ovine model. In this context, the results from this study provide further support for the use of the ovine model.John J Costia, Trevor C Hearn, Nicola L Fazzalar

The role of mineral content in determining the micromechanical properties of discrete trabecular bone remodeling packets

In trabecular bone, each remodeling event results in the resorption and/or formation of discrete structural units called 'packets'. These remodeling packets represent a fundamental level of bone's structural hierarchy at which to investigate composition and mechanical behaviors. The objective of this study was to apply the complementary techniques of quantitative backscattered electron microscopy (qBSEM) and nanoindentation to investigate inter-relationships between packet mineralization, elastic modulus, contact hardness and plastic deformation resistance. Indentation arrays were performed across nine trabecular spicules from 3 human donors; these spicules were then imaged using qBSEM, and discretized into their composite remodeling packets (127 in total). Packets were classified spatially as peripheral or central, and mean contact hardness, plastic deformation resistance, elastic modulus and calcium content calculated for each. Inter-relationships between measured parameters were analysed using linear regression analyses, and dependence on location assessed using Student's t-tests. Significant positive correlations were found between all mechanical parameters and calcium content. Elastic modulus and contact hardness were significantly correlated, however elastic modulus and plastic deformation resistance were not. Calcium content, contact hardness and elastic modulus were all significantly higher for central packets than for peripheral, confirming that packet mineral content contributes to micromechanical heterogeneity within individual trabecular spicules. Plastic deformation resistance, however, showed no such regional dependence, indicating that the plastic deformation properties in particular, are determined not only by mineral content, but also by the organic matrix and interactions between these two components.Lachlan J. Smith, Jeffrey P.Schirer and Nicola L. Fazzalar

A study of cortical bone microdamage and crack morphology utilising confocal microscopy and sequential labelling

The formation and accumulation of microdamage in bone plays an important role in the occurrence of stress and fragility fractures as well as in the initiation of bone remodelling. In this study a novel technique is presented for the investigation of bone microdamage and crack morphology using laser scanning confocal microscopy and sequential labelling with chelating fluorochromes. Compact tension fracture specimens machined from bovine tibial cortical bone, were mechanically tested in a wedge loaded crack-propagating tool. Sequential labelling with xylenol orange and calcein allowed for the crack propagation and microdamage progression to be assessed at each stage using confocal microscopy. Both twodimensional confocal images and three-dimensional z-series reconstructions displayed the formation of a microdamage process zone and wake surrounding the main crack. Further imaging demonstrated the significance of the bone microstructure, such as the vasculature and osteocytes, in the distribution of the microdamage.J. Codrington, J. Kuliwaba, K. Zarrinkalam and N. Fazzalarihttp://www.cp2009.unipr.it/http://www.gruppofrattura.it/index.php?option=com_jombib&task=showbib&id=105