| Osteoporosis is defined as “a disease characterized by low bone mass andmicrostructure deterioration of bone tissue, leading to enhanced bonefragility and consequent increase in fracture risk.There is always a hot topicabout osterporosis.Osteoporosis is a bone disease with typical clinicalsymptoms of pain, stature changes, and traumatic fractures. All thesesymptoms are the result of decreased bone strength. Now as we know, thefactors which could affect the bone strength are decreased bone mass and theregression of microstructure.BMD is always used clinically to estimate the strength of the bone. But,BMD is not a very precise measure to estimate bone strength, for it cannotreflex the true situation of bone mass loss, we cannot know the internalcharacters of bone by merely measuring the bone mass. Moreover, the use ofBMD as an estimate of vertebral bone strength is particularly complicatedby trabecula and bone cortex for the redistribution and transfer of theload.Therefore, researchers are paying more attention to the change of bonemicrostructure, and the following change of trabecular bone biomechanicswith aging. Trabecular bone is the most important structure in bone, thethree-dimensional structure and the connective degree between trabecularbones are called microstructure. The microstructure of cancellous bone iscomplex indeed, including plate-like and rod-like trabecular bone. Micro-CTis a new technique and now widely used in the study of trabecular bone andother bone microstructure and it is very effective to measure bonemicrostructure. However, there are shortcomings about micro-CT. Theexperimental method in prior studies was based on the duality of cancellousbone through the CT threshold. When the threshold was set high, the numberof trabecular bone was lost. Any soft tissue was considered as the bonetrabecula while the threshold was set low. Because there is no uniforminternational CT threshold criterion, the settings of CT thresholds various indifferent types of CT and micro-CT or even scanning process. This isprobably the main reason for the contradictory results in previousinvestigations. In this study, we used the Scanning Electron Microscope(SEM) to measure human lumbar microstructure parameters. Biomechanicsstrength of bone is also an important index about bone growing andmetabolism. Elastic modulus of bone trabecula is a parameter of bonetoughness, and ultimate load reflects the bone structural mechanics.Biomechanical strength can reflect bone mass, connectivity of bonestructure, thickness of bone cortex and the material characters of bonegenerally. The purpose of our study was twofold. First, we wanted to give anestimate of the relationships between the cancellous bone microstructure ofvertebra, BMD, and Mechanical strength. Second, we wanted to providewith the theoretical support to the relationships between age and the fracturerisk, and the treatments of osteoporosis. Experimental methods: Weanalyzed forty-eight fresh L3vertebral bodies donated by48men, aged10-70years old. We grouped the vertebrae into six age categories, thus:group A:10to19years old; group B:20to29years old; group C:30to39years old; group D:40to49years old; group E:50to59years old; group F:60to69years old. Each group consisted of8centrums. After removing softtissue and subsidiary structures, leaving only the vertebral body, vertebralbodies from each age group were thawed at room temperature and cut intotwo halves, along the median sagittal plane. Each half was then cut into a of12×12mm (length×width) specimen which retained the upper and lowerend-plates. Choosing one group and imaged with a scanning electronmicroscope from the upper end-plate to the lower end-plate. Morphologicalanalysis and measurement of trabecular bone and collagen fibrils wereperformed using efilm2.12. Using universal material testing machine(Shimadzu AG-107A) to test the biomechanics of trabecular bone,the elasticmodulus and ultimate load were calculated based on the observed data.Eight remaining specimens were milled in the frozen state at an average sizeof7×7×20mm (length×width×height) as regular test specimens. Aftermeasuring the volume of each test specimen trabecular as Va, they were repeatedly washed with water, soaked in a heparin solution, then washedwith normal saline in order to completely remove blood, marrow and tissuedebris in the medullary cavity. According to the Archimedes principle, thevolume of each test specimen trabecular was measured as Vb, thus:Apparent density=W/Va; and volume ratio=Vb/Va. The SPSS17.0statistical software package was used for statistical analysis.Results:1、Microstructure of trabecular bone under SEM Withinthe20-29years age group, the bone collagen cross-linked into uniformcollagen fibers, and the width of each collagen fiber was approximately2-3μm. The fibers were closely arranged, and the orientation was consistent.The fibrils were connected obliquely by the thinner collagen fibers forreinforcement. With ageing, the bone mass decreased, the cross-linkingability of the collagen declined, and the widths of the collagen fibrils werenot uniform, the trabecular bones were not consistent. And the arrangementof the fibrils was loose, sparse and disordered, and the orientation of theoblique collagen fibers between them was disorganized. This change wasparticularly evident from age group40-49years to50-59years old.2、The morphologic measuring of trabecular bone （1）From group(20～29years old)to group (10～19years old),the width data of verticaltrabeculae and the horizontal trabeculae dramatically changed, this change was statistically significant (P <0.05). From group (30～39years old) togroup (20～29years old), the width data of the vertical trabeculae andhorizontal trabeculae dramatically changed, it is statistically significant.(P <0.01). From group (40～49years old) to group (30～39years old) there wasno significant difference in the width data of vertical trabeculae andhorizontal trabeculae,there was no statistical significance (P>0.05). Fromgroup(50～59) to group (40～49) there was no significant difference in thewidth data of vertical trabeculae and horizontal trabeculae,there was nostatistical significance (P>0.05). From group (60～69years old) to group(50～59years old), there was no significant change in the width data ofvertical trabeculae and horizontal trabeculae, there was no statisticalsignificance(P>0.05).（2）From group (20～29years old) to group (10～19years old), the data of the horizontal and vertical Tb.Sp significantlychanged,this change was statistically significant (P <0.05). From group(30～39years old) to group (20～29years old), the data of the horizontaland vertical Tb.Th significantly changed, this change was statisticallysignificant (P<0.01). From group (40～49years old) to group (30～39yearsold), there were no evident change in the data of the horizontal and verticalTb.Sp and the narrow cavity width, there was no statistical significance (P>0.05).From group (50～59years old) to group (40～49years old), therewere no significant change in the data of the horizontal and vertical Tb.Sp,there was no statistical significance (P>0.05). From group (60～69years old) to(50～59years old) the data of the horizontal and vertical Tb.Spsignificantly changed, this change was statistically significant.(P <0.05（)3）From group (20～29years old) to group (10～19years old),there was nosignificant change in the data of the tabular Tb., no statistical significanceexisted (P>0.05); From group (30～39years old) to group (20～29yearsold), there was significant change in the thickness data of the tabular Tb.,this change was statistically significant.(P<0.01).From group (40～49years old) to group (30～39years old), there was no evident change in thethickness data of tabular Tb.,no statistical significance existed(P>0.05).From group (50～59years old) to group (40～49years old), the data of thetabular Tb. were close to each other (P>0.05).From (60～69years old) togroup (50～59years old), there was no significant change in the thicknessdata of tabular Tb.(P>0.05).3、BMD of vertebral cancellous bone The data of the apparentdensity and volume ratio changed significantly from group (20～29yearsold) to group (10～19years old), this change was statistically significant(P<0.01). The data of the apparent density and volume ratio changedsignificantly from (30～39years old) to group (20～29years old), thischange was statistically significant (P<0.01).From group (40～49years old)to group (30～39years old)and from group (50～59years old) to group(40～49years old),there was no evident change in the data of the apparentdensity and volume ratio, there was no statistical significance(P>0.05). There was no significant change in the data of the apparent density andvolume ratio from group (60～69years old) to group (50～59years old), nostatistical significance existed (P>0.05).4、Biomechanical analysis of vertebral cancellous bone From group(20～29years old) to group (10～19years old), the data of the elasticmodulus and the ultimate load changed significantly, this change wasstatistically significant(P<0.01). From group (30～39years old) to group(20～29years old), the data of the elastic modulus and the ultimate loadchanged significantly, this change was statistically significant (P <0.01).From group (40～49years old) to group (30～39years old), there was noobvious change in the data of elastic modulus and the ultimate load(P>0.05).From group (50～59years old) to group (40～49years old), thedata of the elastic modulus and the ultimate load changed significantly, thischange was statistically significant (P<0.05). From group (60～69years old)to group (50～59years old), there was no obvious change in the data ofelastic modulus, no statistical significance existed (P>0.05).Conclusion: From age10～70years old Chinese men, with ageing, thehorizontal and vertical Tb. Th and the thickness of tabular Tb. decreased;and the horizontal and vertical Tb.Sp gradually increased. However,cancellous bone density, ultimate load and elastic modulus decreased withageing. We therefore conclude that age is associated with the change of microstructure, BMD, and biomechanics of vertebral cancellous bone, andthus our study contributes a theoretical basis for the study of osteoporosisand the increased risk of bone fracture with ageing. |
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