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Many natural structures use a foam core and solid outer shell to achieve high strength and stiffness with relatively small amounts of mass. Biological foams, however, must also resist crack growth. The process of crack propagation within the struts of a foam is not well understood and is complicated by the foam microstructure. We demonstrate that in cancellous bone, the foam-like component of whole bones, damage propagation during cyclic loading is dictated not by local tissue stresses but by heterogeneity of material properties associated with increased ductility of strut surfaces. The increase in surface ductility is unexpected because it is the opposite pattern generated by surface treatments to increase fatigue life in man-made materials, which often result in reduced surface ductility. We show that the more ductile surfaces of cancellous bone are a result of reduced accumulation of advanced glycation end products compared with the strut interior. Damage is therefore likely to accumulate in strut centers making cancellous bone more tolerant of stress concentrations at strut surfaces. Hence, the structure is able to recover more deformation after failure and return to a closer approximation of its original shape. Increased recovery of deformation is a passive mechanism seen in biology for setting a broken bone that allows for a better approximation of initial shape during healing processes and is likely the most important mechanical function. Our findings suggest a previously unidentified biomimetic design strategy in which tissue level material heterogeneity in foams can be used to improve deformation recovery after failure.

Context: Polygonum amplexicaule D. Don var. sinense Forb. (Polygonaceae) (PAF) is a well known traditional herb used to treat some diseases, such as fractures, rheumatoid arthritis, muscle injury, and pain. However, its pharmacological mechanism of promoting the healing of fractures is still unknown., Objective: The present study was designed to investigate the effects of PAF ethanol extracts on the proliferation and differentiation of osteoblastic MC3T3-E1 cell in vitro, thereby to illuminate the pharmacological mechanism to promote the healing of fractures., Materials and Methods: The effects of PAF ethanol extracts on MC3T3-E1 cell proliferation and differentiation were detected by using CCK-8, cell cycle, alkaline phosphatase (ALP), and prostaglandin E(2) (PGE(2)) assays in vitro., Results: The results showed that PAF ethanol extracts significantly stimulated cell proliferation at 0.1-100 μg/mL and the proportion of cells in S-phase increased from 16.33 to 27.29% in osteoblastic MC3T3-E1 cells. Moreover, PAF ethanol extracts increased ALP expression in MC3T3-E1 cells at the concentration from 0.1 to 100 μg/mL and inhibited PGE(2) production induced by TNF-α in osteoblasts at the concentrations ranging from 10 to 100 μg/mL in MC3T3-E1 osteoblasts., Discussion and Conclusion: These results indicated that PAF directly stimulates cell proliferation and differentiation of osteoblasts; therefore, this study preliminarily explored the pharmacological mechanism of PAF to promote the healing of bone rheumatism and various fractures.

The ability to assess a patient's risk of fracture is fundamental to the clinical role of bone densitometry. Fracture discrimination is quantified by the relative risk (RR), defined as the increased risk of fracture for a 1 standard deviation decrease in bone mineral density (BMD). The larger the value of RR, the more effective measurements are at identifying patients at risk of fracture. Epidemiological studies show that RR values for predicting the risk of any fracture are approximately the same for all BMD measurement sites. In this study, we show theoretically that this interesting observation is predictable and a consequence of two related observations: (1) that fracture prediction by BMD measurement sites distant from the fracture site is quantitatively explained by the correlation of BMD measurements and (2) that all correlation coefficients between distant BMD sites are comparable, with values in the range r = 0.55-0.65. The first of these conditions (referred to as the correlation hypothesis) is important because it sets a lower limit on the RR values at distant BMD sites on the assumption that measurements at these sites contain no independent information about fracture risk over and above that provided by their correlation with the fracture site BMD. If the correlation hypothesis is true, the present study points to the importance of the correlation coefficient between BMD sites as a key index that is indicative of the ability of different types of measurement to predict fracture risk. If, on the contrary, the correlation hypothesis is not valid, there is scope to improve bone densitometry by further studies to better identify those measurements that do provide independent information about fracture risk and how best to integrate this information with existing techniques to improve decision making.

It is widely believed that the most reliable BMD measurement for predicting fracture risk at any given skeletal site is one made at the fracture site itself. This study examines the hypothesis that the ability of BMD measurements at other distant sites in the skeleton remote from the fracture site to predict fracture risk is due to their correlation with the BMD measurements at the fracture site. We refer to this assumption as the correlation hypothesis. We show that the correlation hypothesis predicts the relationship betadist = rbetafrac, where beta is the gradient of the exponential relationship between fracture risk and Z-score, betafrac is the beta-value for the fracture site, betadist the beta-value for the distant BMD site, and r is the correlation coefficient between the Z-scores at the two sites. In practice it is important to consider the effect of BMD measurement errors on the (r, beta) relationship. We show that the effect of errors at the distant site is to reduce betadist and r in a way that preserves their original relationship. When errors at the fracture site are taken into account the effect on the (r, beta) plot is for the point representing the fracture site to fall below the extrapolation of the straight-line relationship predicted for the points representing the distant BMD sites. We tested the correlation hypothesis by using data from the Study of Osteoporotic Fractures to examine the (r, beta) plots for hip, spine and forearm fractures. For the hip the data are consistent with a straight-line relationship and suggest that measurements made at other sites provide no additional information about fracture risk over and above that provided by hip BMD itself. For spine and forearm fractures the data show that distant sites do provide additional information about fracture risk in a way that is quantitatively consistent with the BMD measurement errors reported in cadaver studies. It is clear that random BMD errors at the fracture site cause loss of information about fracture risk and that some of this lost information is recoverable from measurements made at other sites in the skeleton. Overall, this study points to BMD correlation as an important factor in explaining the ability of measurements made at distant sites to predict fracture risk.

Corticosteroid treatment diminishes bone mass and alters bone quality. The objective was to evaluate bone in corticosteroid-treated patients and controls and in fractured and non-fractured patients treated with corticosteroids using both X-ray densitometry (DEXA) and ultrasound. We evaluated 34 women aged 58 +/- 14 years (X +/- SD), who had been on long-term low dose prednisone therapy for at least 6 months, and who had never received specific treatment for osteoporosis. Bone mineral density of total skeleton (TS), lumbar spine (LS), femoral neck (FN), and vertebral morphometry (MXA) were measured by DEXA. Speed of sound (SOS), broadband ultrasound attenuation (BUA) and stiffness were measured using an Achilles Plus system. Forty-two healthy women served as controls. Both densitometric and ultrasound parameters in the patients were significantly diminished compared with controls: TS: P < 0.002, LS: P < 0.025, FS: P < 0.005, Stiffness: P < 0.001, BUA: P < 0.002 and SOS: P < 0.002. The percentage of patients with a Z score below -2 was higher in Stiffness and BUA: 38% and 47%, respectively, compared with a range of 16-24% in the other parameters (P < 0.05 BUA vs. DEXA measurements). Eleven patients with previous bone fracture had values lower than the non-fractured patients, both according to DEXA and ultrasound measurements, but the difference was only significant for BUA (P < 0.02). BUA of the calcaneus was more effective in detecting the specific skeletal alterations and fracture risk of the group of patients receiving chronic corticosteroid treatment.