Robert E. Day

Prediction of thoracic and lumbar vertebral body compressive strength: correlations with bone mineral density and vertebral region.

The bone density of thoracolumbar vertebral columns (T1 to L5) from 18 individuals was measured using quantitative computed tomography and dual energy x-ray absorptiometry. Three hundred six isolated vertebral bodies were tested in a materials test device to determine their compressive strength. Between T1 and L5 the mean segmental increase in bone mineral content was 0.3 g, while the corresponding mean decrease in trabecular density was 4.7 HU. Midvertebral body cross-sectional area increased by an average of 46 mm2 per segment and the mean segmental increase in compressive strength was 0.17 kN. Compressive strength was significantly correlated with bone mineral density measured with dual energy x-ray absorptiometry (r = 0.86). Vertebral trabecular density samples measured with quantitative computed tomography were poorly correlated with compressive strength (r = 0.28); however, this was improved when the trabecular density was multiplied by the midvertebral body cross-sectional area (r = 0.83). This study provides information concerning the relationships between density and mechanical properties of all thoracic and lumbar vertebral bodies across a wide age range. While the load-bearing capacity of the vertebral bodies is largely dependent on their geometry and bone density, this relationship has been only extensively tested for the lumbar spine. This study extends these observations over the lumbar and thoracic regions to provide a comprehensive analysis of the strength characteristics of each vertebral body. This is particularly important given the paucity of data on the thoracic spine where age-related vertebral fractures predominate. These data provide a basis for the development of models to predict the potential for thoracolumbar fractures in the elderly vertebral column.

Three-dimensional measurement of lumbar spine kinematics for fast bowlers in cricket.

OBJECTIVE: To determine whether the three-dimensional (3-D) lumbar spine kinematics for the mixed fast bowling technique differed to those of the side-on and front-on fast bowling techniques. BACKGROUND: It has been previously shown that bowlers who utilise a mixed bowling technique are more likely to show lumbar spine pathology than those who bowl with either the side-on or front-on techniques. METHODS: An electromagnetic device (3-Space(R)Fastrak(TM)) operating at 120 Hz captured range of motion and 3-D lumbar spine kinematics during the delivery stride of 20 young high performance subjects. The trajectory of shoulder and pelvic girdle markers were simultaneously captured and these data were used to classify bowlers into either a side-on, front-on or mixed technique group. RESULTS: No significant differences (P<0.004) existed between the side-on/front-on and mixed groups for 12 selected variables derived from the lumbar spine kinematic data. However, an examination of effect sizes revealed evidence that the mixed group showed: a greater amount of left lateral bend and an extended lumbar spine at front foot impact; a body position further from a neutral orientation at lease; and a greater range of motion and angular velocity of the trunk in the lateral bending and flexion/extension axes. CONCLUSIONS: Selected lumbar range of motion and velocity measures tended to be higher for mixed bowlers than side-on/front-on bowlers. RELEVANCE: Overuse injuries to fast bowlers in bricket are common. To better understand the mechanics of injury it is necessary to understand the 3-D rotations of the lumbar spine during this activity.

Ex vivo estimation of thoracolumbar vertebral body compressive strength : The relative contributions of bone densitometry and vertebral morphometry

The estimation of vertebral fracture risk in individuals with suspected osteopenia is commonly based on measurements of lumbar spine bone density. The efficacy of vertebral size and deformity, as assessed by vertebral morphometry, in the prediction of fractures has been less studied. In an ex vivo investigation the regional relationships between vertebral size, vertebral deformity, bone density and compressive strength throughout the thoracolumbar spine were examined. In 16 vertebral columns (T1–L5) the bone mineral content (BMC) and bone mineral density (BMD) of each segment were measured using lateral projection dual-energy X-ray absorptiometry, and the vertebral cancellous density (VCD) and mid-vertebral cross-sectional area (CSA) measured using quantitative computed tomography. Vertebral body heights were determined from mid-sagittal CT scans, and vertical height ratios calculated for each segment. The failure load and failure stress of the isolated vertebral bodies were determined using a material testing device. Separate analyses were performed for the upper (T1–4), middle (T5–8) and lower (T9–12) thoracic, and lumbar (L1–5) segments. In all regions, failure load was strongly correlated with BMD (r=0.82–0.86), moderately correlated with VCD (r=0.60–0.71) and vertebral height (r=0.22–0.49), and poorly correlated with the height ratios (r=0.04–0.33). Failure stress was best predicted by BMD (r=0.73–0.78) and VCD (r=0.70–0.78) but was poorly correlated with all morphometric variables (r=0.01–0.33). The segmental correlations between BMD and VCD ranged fromr=0.49 tor=0.79. For all regions, BMD and VCD were included in the stepwise regression models for predicting failure load and failure stress. Either the mid-vertebral height or CSA were included in all the failure load models, while mid-vertebral height was included in only one of the failure stress models. The results suggest that vertebral deformity and size (as assessed by vertebral morphometry) make only a minor contribution to the prediction of vertebral strength additional to that provided by bone densitometry alone. The consistent regional relationships between variables appear to support the practice of global fracture risk assessment based on lumbar spine densitometry.

Formalin fixation effects on vertebral bone density and failure mechanics: an in-vitro study of human and sheep vertebrae.

Vertebral bone density of two human vertebral specimens was evaluated using dual-anergy X-ray absorptiometry and single-energy quantitative computed tomography immediately before and after 4 weeks of fixation. The repeated QCT assessment of these segments produced a mean rate of change of 1.17 HU/month, while for DXA the mean rate of change was -0.002 g/month for BMC and -0.0004 g/cm(2)/month for BMD. Ten fresh and 10 fixed sheep lumbar spines underwent absorptiometry before being sectioned into units comprising a central vertebra and adjacent intervertebral discs, plus 1 cm of the flanking vertebral end-plate for embedding into bone cement. The fixed sheep spines underwent a repeat scan after 4 weeks in 10% formalin. Mechanical testing produced a significantly lower average failure load for unfixed specimens (9.3 kN) than for the fixed material (10.8 kN). Failure strain was not significantly different between groups. Linear regression showed a high correlation of BMC values before and after 4 weeks of formalin fixation, while the slopes of the regression for BMD and failure load of both fresh and fixed groups were not significantly different. While formalin fixation may result in a slight increase in compressive strength this does not appear to be associated with a systematic change in mineral density.

Heat treatment of Ti‐6Al‐7Nb components produced by selective laser melting

Purpose – The purpose of this paper is to describe a preliminary investigation into the heat treatment of Ti‐6Al‐7Nb components that had been produced via selective laser melting (SLM).Design/methodology/approach – Bars of Ti‐6Al‐7Nb were produced using SLM by MCP‐HEK Tooling GmbH in Lubeck, Germany. These bars were then subjected to a range of heat treatments and the resultant microstructure evaluated with respect to its likely effect on fatigue.Findings – It was found that the as received material consisted of an α′ martensitic structure in a metastable β matrix. Evidence of the layer‐wise thermal history was present, as were large (up to ∼500 μm) pores. Solution treatment at 955°C (below the β transus) did not completely disrupt this layered structure and is therefore not recommended. When solution treatment was performed at 1,055°C (above the β transus) a homogeneous structure was produced, with a morphology that depended on the post‐solution treatment cooling rate. It was concluded that the most prom...

In-vitro relationships between vertebral body density, size, and compressive strength the elderly thoracolumbar spine

The bone density of thoracolumbar vertebral columns (T1-L2) from 12 individuals having a mean age of 73 years was examined using quantitative computed tomography and dual energy X-ray absorptiometry. Spinal units, comprising three vertebrae, from different regions were then tested for compressive strength in a materials test device. Results showed segmental variations in trabecular and integral bone density of the vertebral bodies and their capacity for load bearing. Failure strength increased craniocaudally, whereas failure stress (load/cross-sectional area) decreased. Vertebral compressive strength was moderately correlated with bone mineral density as assessed with dual energy X-ray absorptiometry. In contrast, trabecular bone density determined from quantitative computed tomography was a poor predictor of compressive strength, as was bone mineral content. Use of an integral measure of bone density may provide a more practical guide to bone fragility.

Endogenous glucocorticoid signalling in osteoblasts is necessary to maintain normal bone structure in mice

The role of endogenous glucocorticosteroids (GC) in bone development is ill-defined. Using the Col2.3-11betaHSD2 transgenic (tg) mouse model, we examined the effect of osteoblast-targeted disruption of intracellular GC signalling on bone growth and strength, and its modulation by factors such as age, gender and skeletal site. Tibiae and L3 vertebrae of 3 and 7-week-old, male and female wild type (WT) mice and their tg, age and sex matched littermates were analysed by micro-CT and mechanical testing. Data were analysed separately for 3 and 7-week-old mice by 2-way ANOVA using genotype (WT, tg), gender and their interactions as factors. Transgenic mice were characterised by lower bone volume, lower trabecular number and higher trabecular separation in tibial trabecular bone, as well as lower tibial cortical bone area and periosteal and endosteal perimeters. These changes resulted in a marked decrease in mechanical bone strength and stiffness in sexually mature, 7-week-old mice. In the tibia, the observed transgene effect was present in 3 and 7-week-old animals, indicating that the biological effect of disrupted GC signalling was independent of sexual maturity. This was not the case for the vertebral bones, where significant differences between tg and WT mice were seen in 7 but not in 3-week-old animals, suggesting that the effects of the transgene at this site may be modulated by age and/or changes in circulating sex hormone levels. Taken together, our results demonstrate that endogenous glucocorticoids may be required for normal bone growth but that their effect on bone structure and strength varies according to the skeletal site and sexual maturity of the animals.

Corticosterone selectively targets endo-cortical surfaces by an osteoblast-dependent mechanism

BACKGROUND The pathogenesis of glucocorticoid-induced osteoporosis remains ill defined. In this study, we examined the role of the osteoblast in mediating the effects of exogenous glucocorticoids on cortical and trabecular bone, employing the Col2.3-11βHSD2 transgenic mouse model of osteoblast-targeted disruption of glucocorticoid signalling. METHODS Eight week-old male transgenic (tg) and wild-type (WT) mice (n=20-23/group) were treated with either 1.5 mg corticosterone (CS) or placebo for 4 weeks. Serum tartrate-resistant acid phosphatase 5b (TRAP5b) and osteocalcin (OCN) were measured throughout the study. Tibiae and lumbar vertebrae were analysed by micro-CT and histomorphometry at endpoint. RESULTS CS suppressed serum OCN levels in WT and tg mice, although they remained higher in tg animals at all time points (p<0.05). Serum TRAP5b levels increased in WT mice only. The effect of CS on cortical bone differed by site: At the endosteal surface, exposure to CS significantly increased bone resorption and reduced bone formation, resulting in a larger bone marrow cavity cross-sectional area (p<0.01). In contrast, at the pericortical surface bone resorption was significantly decreased accompanied with a significant increase in pericortical cross-sectional area (p<0.05) while bone formation remained unaffected. Vertebral cortical thickness and area were reduced in CS treatment mice. Tg mice were partially protected from the effects of exogenous CS, both on a cellular and structural level. At the CS doses used in this study, trabecular bone remained largely unaffected. CONCLUSION Endocortical osteoblasts appear to be particularly sensitive to the detrimental actions of exogenous glucocorticoids. The increase in tibial pericortical cross-sectional area and the according changes in pericortical circumference suggest an anabolic bone response to GC treatment at this site. The protection of tg mice from these effects indicates that both catabolic and anabolic action of glucocorticoids are, at least in part, mediated by osteoblasts.

Programmable mechanical stimulation influences tendon homeostasis in a bioreactor system

Identification of functional programmable mechanical stimulation (PMS) on tendon not only provides the insight of the tendon homeostasis under physical/pathological condition, but also guides a better engineering strategy for tendon regeneration. The aims of the study are to design a bioreactor system with PMS to mimic the in vivo loading conditions, and to define the impact of different cyclic tensile strain on tendon. Rabbit Achilles tendons were loaded in the bioreactor with/without cyclic tensile loading (0.25 Hz for 8 h/day, 0–9% for 6 days). Tendons without loading lost its structure integrity as evidenced by disorientated collagen fiber, increased type III collagen expression, and increased cell apoptosis. Tendons with 3% of cyclic tensile loading had moderate matrix deterioration and elevated expression levels of MMP‐1, 3, and 12, whilst exceeded loading regime of 9% caused massive rupture of collagen bundle. However, 6% of cyclic tensile strain was able to maintain the structural integrity and cellular function. Our data indicated that an optimal PMS is required to maintain the tendon homeostasis and there is only a narrow range of tensile strain that can induce the anabolic action. The clinical impact of this study is that optimized eccentric training program is needed to achieve maximum beneficial effects on chronic tendinopathy management. Biotechnol. Bioeng. 2013; 110: 1495–1507.

The Royal Perth Hospital method for the design and manufacture of titanium cranioplasty plates.

b o oyal Perth Hospital designs and manufactures 40–50 ustom-made titanium cranioplasty plates each year, and they ange in size from roughly 50 mm to complete bifrontal craial replacements. The method has evolved over the past ecade into a robust procedure that incorporates computer odelling, rapid-prototyping, and highly-skilled production ngineering. A high resolution helical multislice computed tomoraphic (CT) scan (1.0 mm slice thickness, 1.0 mm slice pacing) is taken of the patient. The CT data are stored and ransferred by PACS in DICOM format. The software packge Mimics (Materialise®, NV Leuven, Belgium) is used to reate a virtual three-dimensional model of the skull. Care s taken to remove the segments of any resorbed bone flap r other metalwork that will be excised during operation hen the titanium plate is implanted (Fig. 1A). The model is xported from Mimics in the .STL format. A rapid-prototype model of the defect is created from he .STL file using the Catalyst EX software (Stratasys®, den Prairie, Minnesota, USA) and a Dimension SST1200es hree-dimensional printer. The .STL file is imported into he software package FreeForm® Modeling PlusTM (Sens-