Regional variations in discrete collagen fibre mechanics within intact intervertebral disc resolved using synchrotron computed tomography and digital volume correlation.

Many soft tissues, such as the intervertebral disc (IVD), have a hierarchical fibrous composite structure which suffers from regional damage. We hypothesise that these tissue regions have distinct, inherent fibre structure and structural response upon loading. Here we used synchrotron computed tomography (sCT) to resolve collagen fibre bundles (∼5µm width) in 3D throughout an intact native rat lumbar IVD under increasing compressive load. Using intact samples meant that tissue boundaries (such as endplate-disc or nucleus-annulus) and residual strain were preserved; this is vital for characterising both the inherent structure and structural changes upon loading in tissue regions functioning in a near-native environment. Nano-scale displacement measurements along >10,000 individual fibres were tracked, and fibre orientation, curvature and strain changes were compared between the posterior-lateral region and the anterior region. These methods can be widely applied to other soft tissues, to identify fibre structures which cause tissue regions to be more susceptible to injury and degeneration. Our results demonstrate for the first time that highly-localised changes in fibre orientation, curvature and strain indicate differences in regional strain transfer and mechanical function (e.g. tissue compliance). This included decreased fibre reorientation at higher loads, specific tissue morphology which reduced capacity for flexibility and high strain at the disc-endplate boundary. STATEMENT OF SIGNIFICANCE: The analyses presented here are applicable to many collagenous soft tissues which suffer from regional damage. We aimed to investigate regional intervertebral disc (IVD) structural and functional differences by characterising collagen fibre architecture and linking specific fibre- and tissue-level deformation behaviours. Synchrotron CT provided the first demonstration of tracking discrete fibres in 3D within an intact IVD. Detailed analysis of regions was performed using over 200k points, spaced every 8 µm along 10k individual fibres. Such comprehensive structural characterisation is significant in informing future computational models. Morphological indicators of tissue compliance (change in fibre curvature and orientation) and fibre strain measurements revealed localised and regional differences in tissue behaviour.

Synchrotron tomography of intervertebral disc deformation quantified by digital volume correlation reveals microstructural influence on strain patterns.

The intervertebral disc (IVD) has a complex and multiscale extracellular matrix structure which provides unique mechanical properties to withstand physiological loading. Low back pain has been linked to degeneration of the disc but reparative treatments are not currently available. Characterising the disc's 3D microstructure and its response in a physiologically relevant loading environment is required to improve understanding of degeneration and to develop new reparative treatments. In this study, techniques for imaging the native IVD, measuring internal deformation and mapping volumetric strain were applied to an in situ compressed ex vivo rat lumbar spine segment. Synchrotron X-ray micro-tomography (synchrotron CT) was used to resolve IVD structures at microscale resolution. These image data enabled 3D quantification of collagen bundle orientation and measurement of local displacement in the annulus fibrosus between sequential scans using digital volume correlation (DVC). The volumetric strain mapped from synchrotron CT provided a detailed insight into the micromechanics of native IVD tissue. The DVC findings showed that there was no slipping at lamella boundaries, and local strain patterns were of a similar distribution to the previously reported elastic network with some heterogeneous areas and maximum strain direction aligned with bundle orientation, suggesting bundle stretching and sliding. This method has the potential to bridge the gap between measures of macro-mechanical properties and the local 3D micro-mechanical environment experienced by cells. This is the first evaluation of strain at the micro scale level in the intact IVD and provides a quantitative framework for future IVD degeneration mechanics studies and testing of tissue engineered IVD replacements. STATEMENT OF SIGNIFICANCE: Synchrotron in-line phase contrast X-ray tomography provided the first visualisation of native intact intervertebral disc microstructural deformation in 3D. For two annulus fibrosus volumes of interest, collagen bundle orientation was quantified and local displacement mapped as strain. Direct evidence of microstructural influence on strain patterns could be seen such as no slipping at lamellae boundaries and maximum strain direction aligned with collagen bundle orientation. Although disc elastic structures were not directly observed, the strain patterns had a similar distribution to the previously reported elastic network. This study presents technical advances and is a basis for future X-ray microscopy, structural quantification and digital volume correlation strain analysis of soft tissue.

Dental attendance and dental health behaviour in children from deprived and non-deprived areas of Salford, north-west England.

AIMS: Firstly, to investigate reported oral health behaviours and changes in behaviour of 3-year-old children in deprived and non-deprived wards of Salford, UK. Secondly, to examine differences in this behaviour between symptomatic and non-symptomatic attenders. Thirdly, to note sources of dental health advice given to parents. DESIGN: Interviews using structured questionnaires. SETTING: Play groups and nurseries in Salford, North-West England. METHOD: Interviews with representative groups of mothers of 3-year-old children attending play groups and nurseries in selected deprived and non-deprived wards, enquiring about dental attendance, dental health behaviour and changes in these resulting from dental advice. RESULTS: Mothers of 284 children were interviewed. Over three-quarters of the children were reported to have a drink or food at bed-time, or during the night, often containing non-milk extrinsic sugars (NMES); more in the deprived wards. All parents reported a tooth brushing habit with over 90% using a fluoride toothpaste, those in non-deprived wards beginning earlier in life and brushing more frequently. Most parents claimed that their children had seen a dentist at some time; more in the non-deprived wards. More children in deprived wards were symptomatic attenders sometimes experiencing extractions under general anaesthesia. More parents in deprived wards remembered receiving dental health advice from the dental team and were more inclined to act on that advice. CONCLUSION: Children from deprived wards were reported to have different dental health habits from those from non-deprived wards. They were more likely to be fed NMES in food and drinks at bedtime, begin brushing later in life and brush less frequently and attend the dentist symptomatically. Their parents claimed to have received more dental health advice from the dental team and were more likely to act on that advice.

Community defibrillation in the Scottish Highlands.

Prompt defibrillation after cardiac arrest is necessary to save life. Inexpensive systems providing defibrillation facilities in the community of the Highlands have been devised, one for Inverness town practices, and one for rural practices. Both systems work by 'blind' defibrillation, once the clinical diagnosis of cardiac arrest is confirmed. Acute anti-arrhythmic drugs and intravenous infusions were not available. The systems functioned satisfactorily with general acceptance by the general practices concerned.