Biomechanical properties of human os calcanei: relationships with bone density and fractal evaluation of bone microarchitecture.

The relationship between bone strength and bone mass is well established. The link between trabecular microarchitecture and biomechanical properties has been less extensively explored. To address this question, we have tested the mechanical behaviour of calcaneus bone samples and investigated the correlations between mechanical properties on the one hand, bone density and fractal analysis of microarchitecture on the other hand. Mechanical properties of 43 human os calcanei were determined by uniaxial compression testing of samples from tuber calcanei. Ash density, bulk density and dual energy X-ray absorptiometry of the samples were measured. Fractal analysis of the trabecular bone on calcaneus radiographs was performed by two estimators derived from the fractional Brownian motion model. The mechanical properties of human os calcis were found to correlate with age and density measurements. Fractal parameters derived from the bone texture analysis showed weaker but significant correlations with bone strength. Fractal analysis of texture could account in part for the variations of bone strength, but in this study cannot explain better than density the mechanical properties of trabecular bone. Nevertheless, it provides a non-invasive means of assessing molecular bone microarchitecture.

["Sunshine at school": a network for training on sun exposure. Assessment of knowledge among 683 children]. / Le soleil à l'école: réseau d'éducation à l'exposition solaire. Evaluation des connaissances chez 683 enfants de CM1 et CM2.

INTRODUCTION: The protection of children from sun exposure appears inadequate. We assessed the knowledge of pre-teenagers, before and after they attended a training session on sun exposure. This investigation was carried out in Orléans and in 5 surrounding cities, from September 2000 to April 2002. MATERIAL AND METHODS: A didactic slide show on sun exposure and photoprotection was presented to 683 children in grade 4 and 5 by a nurse and a dermatologist during 30 informative sessions. The children filled in questionnaires at each training session and then one month later. The questionnaires contained 10 closed questions involving 32 cognitive and behavioral items. RESULTS: Forty-five percent of the children claimed that they were exposed to the sun more than one hour a day during holidays, 14 p. 100 more than 3 hours a day; 26 p. 100 declared they had never been sunburnt; 46 p. 100 said they had been less than 5 times, 15 p. 100 from 5 to 10 times and 12 p. 100 more than 10 times; 74 p. 100 of the children claimed they enjoyed getting sun-tanned; 80 p. 100 knew that sun exposure could lead to serious diseases, while 73 p. 100 realized that contracting sunburns during childhood increases the risk of subsequent skin cancers; 89 p. 100 knew of the necessity of sun-screen use prior to exposure, 94 p. 100 knew that they help to protect the skin whereas 78 p. 100 knew it must be applied on a regular basis; 77 p. 100 of the children had been informed of the importance of sun protection factor; 92 p. 100 of them were aware of the relevance of a cap and sunglasses for protection from the sun, whereas only 45 p. 100 knew of the need for a tee-shirt. DISCUSSION: Our study showed that children are generally aware of the dangers of sun exposure. This might be the result of previously initiated information and prevention campaigns on skin cancers. This study suggests the efficiency of such projects, and the lasting effects of the information received within one month. However, large numbers of children are still overexposed and subsequently suffer from traumas. The appeal of sun embellishment appears to go back to childhood, and should be taken into account from the early stages of childhood in future preventive actions. An efficient policy of education on sun exposure - including teaching tools relevant to each age--still has to be developed.

Fractal analysis of trabecular bone texture on radiographs: discriminant value in postmenopausal osteoporosis.

Trabecular bone microarchitecture cannot be routinely evaluated. We have developed and validated a fractal analysis of trabecular bone texture on calcaneus radiographs. The aim of this work was to evaluate the ability of the fractal analysis to discriminate a group of 39 postmenopausal women with osteoporotic (OP) vertebral crush fractures (68.0 +/- 10.8 years) from an age-matched control group of 39 women (68.0 +/- 10.7 years). The value of the fractal analysis was compared with the value of the femoral neck bone mineral density (FNBMD) and trochanteric bone mineral density (TRBMD). The result is expressed by the parameter Hmean (Hmean = 2 - fractal dimension). Hmean value was 0.691 +/- 0.050 in the OP group versus 0.739 +/- 0.024 in the controls, while FNBMD was 0.598 +/- 0.113 g/cm2 versus 0.645 +/- 0.109 g/cm2 and TRBMD was 0.512 +/- 0.108 g/cm2 versus 0.594 +/- 0.106 g/cm2 respectively. The statistical significance of the Hmean test (p < 0.0001) was higher than for FNBMD (p < 0.05) and for TRBMD (p = 0.0004). We used a receiver operating characteristic (ROC) curve to check this superiority. The area under the ROC curve was 0.824 for Hmean, 0.633 for FNBMD and 0.727 for TRBMD. This superiority of the Hmean ROC curve was statistically significant versus FNBMD, but not versus TRBMD. In a second analysis, we studied the subgroups of OP patients and controls with overlapping FNBMD or TRBMD values to check whether the fractal dimension test could be discriminant in these subgroups. Significant statistical differences were found for Hmean between OP patients and controls in the overlapping subgroup for FNBMD or TRBMD (respectively p = 0.006 and p < 0.02). These data confirm that the fractal analysis of texture on calcaneus radiographs is able to discriminate OP patients with vertebral crush fracture from controls. This discrimination was stronger than that obtained by FNBMD or TRBMD alone. It was also present when we compared subgroups with overlapping values of FNBMD or TRBMD.

Fractal analysis of bone texture on os calcis radiographs compared with trabecular microarchitecture analyzed by histomorphometry.

Microarchitecture of trabecular bone is an important determinant of bone fragility; to date, its evaluation requires bone biopsy with histomorphometry analysis. Methods of noninvasive characterization of trabecular bone microarchitecture are in development and we have developed and validated a bone texture analysis applied to bone radiographs and based on fractal geometry. The aim of our study was to compare this fractal analysis of trabecular bone texture on radiographs to the trabecular microarchitecture analyzed by bone histomorphometry on os calcis biopsies. Thirty eight ossa calcis from 19 human cadavers were studied. Fractal analysis of the trabecular bone of os calcis radiographs was performed by the maximum likelihood estimator following the fractional brownian motion model. The ossa calcis were dissected, then transcortical biopsy cores focused on the fractal analysis region of interest were obtained. Structural and connectivity parameters were measured with both automatic and semiautomatic analyzers. We have found a significant relationship between the fractal Hmean parameter and structural histomorphometric indices; the best correlation was found with trabecular separation (r = -0.55; P = 0.0004). Based on a stepwise regression analysis, trabecular spacing and trabeculae number together would explain 38% of the variance of the fractal parameter. Although the relationship with connectivity indices was poor, our fractal analysis of os calcis trabecular bone texture on radiographs seemed to partially reflect the trabecular bone microarchitecture.