糖皮质激素对成年大鼠骨量的影响

目的利用双能X线吸收法(DXA)探讨成年大鼠接受糖皮质激素后骨量变化的规律。方法 21只44周龄SD雌性大鼠分别假性去卵巢+未注射糖皮质激素(SHAM组)、摘除双侧卵巢(OVX组)或注射甲基强的松龙[2.5 mg/(kg·d)](PRED组),应用扇形束DXA(QDR-4500A)每4周测定一次全身骨密度(BMD)、骨矿含量(BMC)、骨骼面积(AREA);术后12周处死,测定离体腰椎、股骨、胫骨及其兴趣区的BMD、BMC、AREA。压缩试验测定第二腰椎最大载荷和弹性模量。结果 (1)术后8周开始OVX组体重显著重于同龄SHAM组(8周时,P0.05,12周时P0.01),术后4周开始PRED组体重显著轻于同龄SHAM组(P0.05);(2)术后12周OVX组整体BMC显著高于SHAM组(P0.05),术后8、12周OVX组整体BMC显著高于PRED组(P0.05);(3)术后12周OVX组离体第5、6腰椎BMD及第6腰椎BMC显著低于SHAM组和PRED组(P0.05),PRED组离体各腰椎BMD、BMC、AREA与SHAM组无明显差异;(4)术后12周与SHAM组比较,OVX组离体股骨(-7.42%)、股骨远端(-10.85%)和近端(-6.92%)、胫骨近端(-11.40%)BMD显著降低(P0.05),其中股骨、股骨远端、胫骨近端BMC也显著降低(P0.05);(5)术后12周与SHAM组比较,PRED组离体股骨及各区BMD、BMC、AREA无显著性差异,整体胫骨及各区BMD无显著性差异;(6)术后12周与SHAM组比较,OVX组及PRED组胫骨中远端骨量增加;(7)与SHAM组比较,OVX组最大载荷和弹性模量显著降低,PRED组最大载荷显著降低。结论成熟期大鼠接受甲基强的松龙后,皮质骨和松质骨骨量没有显著变化,DXA检查难以发现其骨丢失情况;力学性能改变提示糖皮质激素更多的是引起骨质量的改变而导致了力学性能的下降及骨折的发生。     

容积性定量CT测量股骨近端骨密度准确性研究

目的通过分别对比容积性定量CT(vQCT)、双能X射线吸收法(DXA)与灰化法测量股骨近端骨密度结果,确定并对比相关性,进行指导临床骨质疏松诊断及治疗。方法选取20个尸体股骨近端标本,先使用DXA骨密度仪扫描,测得骨矿含量(BMC)及骨密度(BMD)。再对标本相同部位行64层螺旋CT扫描,数据导入OsteoCAD软件自动分析得出骨密度值。应用灰化法得出标本灰质量密度。所有资料进行统计分析分别确定并对比vQCT及DXA测量的骨密度值与灰密度之间的相关性。结果vQCT测量股骨颈骨密度与灰质量密度线性相关性较好(r=0.852,P0.01),DXA与灰质量密度的相关性略差(r=0.807,P0.01)。结论vQCT测得的骨密度较DXA与灰质量密度线性相关性更好,可靠性高,对于诊断骨质疏松,预测骨质疏松性骨折,评价、指导骨质疏松骨折手术更有应用价值。     

高原低氧环境下骨质疏松大鼠模型的骨代谢生化指标观察

目的观察高原低氧环境下骨质疏松大鼠模型的骨形成相关生化指标变化,探讨其在高原地区骨质疏松症诊断和监测中的应用。方法选用纯种SD雌性大白鼠72只,随机分为A组(高原去势组)、B组(平原去势组)、C组(高原对照组)和D组(平原对照组)。术后分别在海拔高于3000米的高原和低于500米的平原饲养。并于术后4周、12周和24周测量大鼠的股骨骨密度和血清相关生化指标。结果 12周时,高原和平原饲养的去势大鼠骨密度下降较为显著(P<0.05),且高原去势组骨密度明显低于平原去势组(P<0.05),对照组均无显著变化(P>0.05)。24周,除平原对照组骨密度无显著变化,其它三组骨密度均有显著降低,且高原去势组骨密度明显低于其它组,差异具有统计学意义(P<0.01)。生化指标检测发现,高原饲养组与平原饲养组比较,血清钙浓度无显著性差异(P>0.05)。血清磷离子的含量由高到低为平原对照组、高原对照组、平原去势组和高原去势组,差异具有统计学意义(P<0.05)。碱性磷酸酶在各时间段及各组之间均无明显差异(P>0.05)。不论是去卵巢还是未去卵巢,与平原饲养的大鼠相比,高原饲养的大鼠的血清骨钙素含量始终维持在低水平(P<0.01)。去势组大鼠的血清激素雌二醇的含量显著低于对照组,而饲养于高原后,这种差异更加显著(P<0.01)。结论高原缺氧环境可引起骨代谢异常,并加速骨质疏松发展的进程,联合应用骨密度及血清骨形成生化指标检测有助于高原骨质疏松症的诊断。     

DXA测量BMD与超声测量SOS的比较

目的　本文通过对同一个人的跟骨超声声速(SOS)测量与双能X线吸收法测量腰2-4,股骨近端骨密度(BMD)的临床对比来评价超声骨密度仪测量跟骨的SOS对诊断骨质疏松症的敏感性和与DXA测量BMD的相关性。方法　对523名8～87岁健康人群同时采用DXA测量L2-4,股骨近端(Neck,Ward三角,Troch)BMD和超声骨密度仪测量左跟骨SOS值并进行相关分析。对1006名3～87岁健康人群测量左右跟骨的SOS值。结果　SOS与DXA测量BMD的骨峰值(PBM)均出现在20～39岁,SOS的PBM男性为(1542.83±27.44)m/s,女性为(1531.02±29.96)m/s。40岁以后随着年龄的增加,二者均逐渐下降。健康成人中BMD与SOS的相关系数为0.3～0.6,骨质疏松患者BMD与SOS的相关系数(r=0.16～0.39)较健康人(r=0.33～0.61)低。左右足跟SOS无显著差异,DXA的BMD与SOS诊断骨质疏松症(OP)的符合率为60%。结论　DXA测量BMD与超声SOS为中等相关。建议在单独使用超声骨密度仪测量SOS来诊断OP时,应当参照临床症状和X线的检查全面考虑,以免造成漏诊或误诊。     

可待因类止咳水成瘾治疗前后骨矿密度研究

目的应用双能X线骨密度仪,研究复方磷酸可待因止咳水成瘾者脱毒康复治疗前后骨矿密度的变化。方法以国际临床骨测量学会制定的骨密度测定方法学为标准,分别测量34例止咳水成瘾者经6个月以上脱毒康复治疗前后的骨密度,同时测量31例健康志愿者骨密度。测量体位包括腰椎、股骨近端和非优势侧前臂骨1/3段。比较止咳水成瘾者康复治疗前后骨矿密度的变化及测量Z值的差异。结果复方磷酸可待因止咳水成瘾组腰椎、左侧股骨近端和左侧前臂骨1/3段骨矿密度绝对值减低,皆明显低于健康对照组(t=-8.33、-10.14、-10.41,P均=0.000),测量Z值减低,超过正常值-2.0标准差(-2.0SD)范围,皆明显低于健康对照组(t=-10.84、-9.98、-13.07,P均=0.000),差异有统计学意义。经6个月以上脱毒康复治疗后,该成瘾组3组体位骨矿密度绝对值增加,皆高于治疗前水平(t=8.54、9.42、9.45,P均=0.000),测量Z值未见异常,在正常值-2.0标准差(-2.0SD)范围内,皆高于治疗前水平(t=7.74、8.21、8.79,P均=0.000),差异有统计学意义。结论经6个月以上的脱毒康复治疗后,滥用复方磷酸可待因止咳水产生成瘾的患者腰椎、股骨近端和前臂骨类似骨质疏松的病理变化得到明显改善。     

应用双能X线骨密度仪探讨糖尿病性骨质疏松症的影响因素

目的探讨2型糖尿病患者骨质疏松的影响因素。方法选择2011年9月至2013年3月在内分泌科住院的男性2型糖尿病患者209例为糖尿病组,选择同期体检的健康男性103例为对照组,应用双能X线骨密度仪(DXA)进行正位腰椎(L1-L4)及左侧股骨骨密度(BMD)测定,检测糖化血红蛋白(Hb A1C)、空腹血糖(FPG)及空腹C肽(CP),并进行统计学分析。结果糖尿病组骨量减少、骨质疏松发生率分别为14.35%、13.87%,明显高于对照组(P0.05)。两组检测者随着年龄增加,骨密度均呈下降趋势,50岁以上糖尿病患者腰椎及股骨颈骨密度均明显低于同龄对照组(P0.05)。糖尿病组骨密度多因素相关性分析显示,糖尿病患者骨密度与年龄、病程、Hb A1C呈显著负相关(P0.05),而与体重指数(BMI)、空腹C肽(CP)呈显著正相关(P0.05)。结论 2型糖尿病患者骨量减少及骨质疏松发生率较健康体检者明显升高;高龄、病程长及血糖控制不良是糖尿病患者BMD降低的危险因素。     

成年卵巢切除大鼠模型股骨近端pQCT与DEXA的相关分析

目的　比较pQCT和DEXA两种方法检测成年卵巢切除大鼠模型股骨近端骨密度减少的敏感性 ,同时也分析两者的相关性。方法　 16只 8月龄雌性Wistar大鼠 ,随机分为两组 ,一组为双侧卵巢切除组 (OVX) ,另一组为假手术组 (Sham) ;3个月后 ,动物处死。取股骨标本 ,对股骨近端 6mm区域进行pQCT和DEXA检测 ,对检测结果进行统计分析。结果　aBMC与vBMD呈显著正相关(r=0 82 ,P <0 0 0 1) ;aBMD与vBMD无明显相关性 (r =0 14 ,P >0 0 5 )。aBMC与aBMD呈正相关(r=0 .72 ,P <0 0 5 ) ;vBMC与vBMD无相关性。卵巢切除组的vBMD与假切组相比明显下降 (-8 2 % ,P <0 0 0 1) ,而卵巢切除组的aBMD与假切组相比下降无明显差异 (- 3 0 % ,P >0 0 5 )。结论　pQCT和DEXA的测量结果有一定的相关性 ,但pQCT比DEXA敏感性更高     

GnRH拮抗剂用于卵巢反应不良患者的体外受精胚胎移植

目的:比较促性腺激素释放激素拮抗剂(GnRH-Ant)与激动剂(GnRH-a)分别用于卵巢反应不良患者体外受精胚胎移植(IVF-ET)的结果,寻求更为适合的促排卵方案。方法:①将GnRH-Ant组设为实验组(n=63),口服避孕药(OC)+GnRH-a减量组设为对照组(n=58),比较两组临床用药、实验室结果及妊娠结局;②同一患者先后分别采用GnRH-Ant及OC+GnRH-a减量方案进行自身对照(n=20),比较两组临床用药、实验室结果及妊娠结局。结果:①实验组与对照组在促性腺激素(Gn)用量、获卵数和移植胚胎数等方面无明显差异(P>0.05);实验组与对照组移植周期妊娠率无差异(37.29%vs35.29%,P>0.05);实验组周期取消率低于对照组(6.35%vs12.07%),但无显著性差异(P>0.05);实验组与对照组总治疗天数[(9.65±1.60)dvs(19.05±3.94)d],有显著性差异(P<0.05)。②GnRH-a与GnRH-Ant的自身对照,两组Gn用量、获卵数和移植胚胎数无显著差异(P>0.05);GnRH-Ant组移植周期妊娠率明显高于GnRH-a组,但无统计学差异(38.09%vs17.64%,P>0.05);周期取消率低于GnRH-a组(0%vs15%),有显著性差异(P<0.01);总治疗天数GnRH-a组明显高于GnRH-Ant组[(27.74±25.39)dvs(9.91±2.49)d],两者有显著性差异(P<0.05)。结论:对于卵巢反应不良患者的IVF-ET,GnRH-Ant与GnRH-a减量方案相比,可以减少总的治疗时间,降低周期取消率。对于既往采用GnRH-a减量方案失败的患者,再次IVF-ET可以尝试采用GnRH-Ant方案。     

腰椎松质骨CT值与年龄、双能X线骨密度值相关性研究

目的研究女性腰椎松质骨CT值与年龄、双能X线骨密度值的相关性。方法 103例女性住院患者纳入研究对象,所有患者行腰椎骨密度与腰椎螺旋CT检查,双能X线骨密度仪(DXA)测量腰1~4椎体骨密度(BMD)和T值。CT扫描分析腰1~4椎体松质骨CT值。将所有研究对象的年龄、腰1~4椎体CT值、DXA测得BMD值及T值进行收集、整理及统计学处理。结果 1不同年龄段腰1~4椎体松质骨CT值差异具有统计学意义(F=102.5,P0.001);每两个年龄段间的CT值比较差异亦具有统计学意义(P0.001)。组内比较腰1~4椎体之间的CT值没有统计学意义(P0.05)。2按T值将所有研究对象分为3组(骨量正常、骨量减少及骨质疏松症组),各组间腰1~4椎体松质骨CT值差异具有统计学意义(F=248.6,P0.001)。组间两两比较,骨质疏松症组CT值骨量减少组CT值骨量正常组CT值,差异具有统计学意义(P0.001)。组内比较腰1~4椎体的CT值没有统计学意义(P0.05)。3腰1~4椎体BMD值与椎体松质骨CT值呈显著正相关(P0.001)。结论女性腰椎椎体的松质骨CT值随着年龄增长逐渐减低。DXA测得BMD值与腰椎椎体松质骨CT值存在显著正相关。     

去卵巢大鼠胫骨骨小梁的显微CT研究

目的应用显微CT研究去卵巢大鼠胫骨松质骨随时间延长骨小梁密度及微结构的变化。方法50只7月龄雌性SD大鼠随机分为基线组10只、去卵巢组(OVX)和假手术组(sham)各20只。基线组10只实验开始时即处死,OVX组和sham组分别在手术后3周、15周各处死10只,分离保存左侧胫骨,行显微CT扫描。扫描完成后选取距生长板远端0.8mm、层厚0.5mm的骨组织为兴趣区域,进行三维重建,获取骨小梁三维结构图像,并进行松质骨定量分析。结果OVX组与sham组的体积骨密度、骨体积分数(BVF)、骨小梁数量(Tb.N)和骨小梁连接密度3周较15周显著下降,结构模型指数明显增高,提示骨小梁板状形态结构的衰减。3周时OVX组组织骨密度显著低于sham组,15周时两组间无明显差异;而3周时骨小梁间隔与sham组无明显差异,15周时则显著增高。随着去卵巢时间的延长,大鼠胫骨松质骨BVF、Tb.N和骨小梁连接密度进行性下降,但骨小梁厚度(Tb.Th)和组织骨密度却明显升高。15周时Tb.Th为(0.081±0.013)mm,显著高于3周时的(0.061±0.006)mm和基线组的(0.061±0.010)mm;15周时组织骨密度为(691.2±35.3)mg/mm3,显著高于3周时的(624.4±34.4)mg/mm3和基线组的(638.8±61.0)mg/mm3。结论大鼠去卵巢后胫骨松质骨骨量明显丢失,微结构发生改变,而残余骨小梁会因代偿性肥厚和组织骨密度的升高而得到加强。     

Comparison of Radiographic and pQCT Analyses of Healing Rat Tibial Fractures

Fracture healing and callus formation have traditionally been evaluated by using X-ray radiography. Here we compared X-ray radiography and peripheral quantitative computed tomography (pQCT) in evaluating the healing callus of standardized tibial fractures in 141 female rats after a 4- or 8-week follow-up. The results were compared with the tensile (4-week) and compressive (8-week) failure load of the callus. The projectional size of callus, as defined from lateral ex vivo radiographs, correlated significantly with the pQCT-defined cross-sectional area (CSA) of mid-callus. This relationship was dependent on the pQCT attenuation threshold, being higher for the CSA of compact bone (r = 0.85, P < 0.0001) than for the total bone CSA (r = 0.68, P < 0.0001). Radiographically defined callus projectional area also correlated strongly with bone mineral content (BMC) (r = 0.84–0.86, P < 0.0001). The mean optical density of the callus analyzed from the radiographs had only a weak correlation with the pQCT-defined bone mineral density (BMD) of callus. A weak negative relationship was found between CSA and BMD. The optical density analyzed from lateral radiographs did not correlate with the tensile or compressive failure load of callus. Callus size, BMC, and BMD were associated with the compressive failure load, whereas both radiographs and pQCT were poor in explaining the failure load in tension. Received: 28 June 1999 / Accepted: 28 October 1999     

PIXImus Bone Densitometer and Associated Technical Measurement Issues of Skeletal Growth in the Young Rat

The PIXImus dual-energy X-ray absorptiometer (DXA) is designed to measure body composition, bone mineral content (BMC), area (BA), and density (BMD) in mice and rats. The aims of this study were to longitudinally measure BMC, BA, and BMD in growing rats and to identify potential technical problems associated with the PIXImus. Total femur and lumbar DXA measurements, body weight, and length of initially 3-week-old rats (n = 10) were taken at weeks 5, 9, and 14. BMC and BMD of femoral metaphyseal and diaphyseal regions rich in trabecular and cortical bone, respectively, were obtained. Results showed significant increases in body weight, total femur BMC and BMD, lumbar area, length, BMC, and BMD at each time point. There was a significant positive correlation between body weight and total femur BMD (r = 0.97, P < 0.001) as well as lumbar BMD (r = 0.99, P < 0.001). BMD values for the femoral metaphyseal region and the lumbar spine were also positively correlated (r = 0.96, P < 0.01). Several technical issues (e.g., positioning of animals), difficulties (e.g., in analysis of images), and limitations (e.g., inability to detect underdeveloped calcified bone in growing animals and bone edge detection) of the software pertinent to the PIXImus were evident. In conclusion, despite limitations in the software, the PIXImus is a valuable tool for studying skeletal development of growing rats.     

Dual-energy X-ray absorptiometry,peripheral quantitative computed tomography,and micro-computed tomography techniques are discordant for bone density and geometry measurements in the guinea pig

This study aims to examine agreement among bone mineral content (BMC) and density (BMD) estimates obtained using dual-energy X-ray absorptiometry (DXA), peripheral quantitative computed tomography (pQCT), and micro-computed tomography (μCT) against high-resolution μCT and bone ash of the guinea pig femur. Middle-aged (n = 40, 86 weeks) male guinea pigs underwent in vivo followed by ex vivo DXA (Hologic QDR 4500A) scanning for intact and excised femur BMC and areal density. To assess bone architecture and strength, excised femurs were scanned on pQCT (Stratec XCT 2000L) as well as on two μCT scanners (LaTheta LCT-200; Skyscan 1174), followed by three-point bending test. Reproducibility was determined using triplicate scans; and agreement assessed using Bland–Altman plots with reference methods being high-resolution μCT (Skyscan) for BMD and bone ashing for BMC. All techniques showed satisfactory ex vivo precision (CV 0.05–4.3 %). However, bias compared to the reference method was highest (207.5 %) in trabecular bone volume fraction (BV/TV) measured by LaTheta, and unacceptable in most total femur and cortical bone measurements. Volumetric BMD (vBMD) and BV/TV derived by LaTheta and pQCT at the distal metaphysis were biased from the Skyscan by an average of 49.3 and 207.5 %, respectively. Variability of vBMD, BV/TV and cross-sectional area at the diaphysis ranged from ?5.5 to 30.8 %. LaTheta best quantified total femur BMC with an upper bias of 3.3 %. The observed differences among imaging techniques can be attributable to inherent dissimilarity in construction design, calibration, segmentation and scanning resolution used. These bone imaging tools are precise but are not comparable, at least when assessing guinea pig bones.     

Interpretation of whole body dual energy X-ray absorptiometry measures in children: comparison with peripheral quantitative computed tomography

The assessment of bone health in children requires strategies to minimize the confounding effects of bone size on dual energy X-ray absorptiometry (DXA) areal bone mineral density (BMD) results. Cortical bone composes 80% of the total skeletal bone mass. The objective of this study was to develop analytic strategies for the assessment of whole body DXA that describe the biomechanical characteristics of cortical bone across a wide range of body sizes using peripheral quantitative computed tomography (pQCT) measures of cortical geometry, density (mg/mm³), and strength as the gold standard. Whole body DXA (Hologic QDR 4500) and pQCT (Stratec XCT-2000) of the tibia diaphysis were completed in 150 healthy children 6–21 years of age. To assess DXA and pQCT measures relative to age, body size, and bone size, gender-specific regression models were used to establish z scores for DXA bone mineral content (BMC) for age, areal BMD for age, bone area for height, bone area for lean mass, BMC for height, BMC for lean mass, and BMC for bone area; and for pQCT, bone cross-sectional area (CSA) for tibia length and bone strength (stress-strain index, SSI) for tibia length. DXA bone area for height and BMC for height were both strongly and positively associated with pQCT CSA for length and with SSI for length (all P < 0.0001), suggesting that decreases in DXA bone area for height or DXA BMC for height represent narrower bones with less resistance to bending. DXA BMC for age (P < 0.01) and areal BMD (P < 0.05) for age were moderately correlated with strength. Neither DXA bone area for lean mass nor BMC for lean mass correlated with pQCT CSA for length or SSI for length. DXA BMC for bone area was weakly associated with pQCT SSI for length, in females only. Therefore, normalizing whole body DXA bone area for height and BMC for height provided the best measures of bone dimensions and strength. DXA BMC normalized for bone area and lean mass were poor indicators of bone strength.     

Genetic and environmental determinants of volumetric and areal BMD in multi-generational families of African ancestry: the Tobago Family Health Study.

BMD is higher and fracture risk is lower among individuals of African versus European descent, but little is known about the genetic architecture of BMD in the former group. Heritabilities of areal and volumetric BMD were moderate in our large families of African descent but differed for trabecular and cortical BMD. INTRODUCTION: Populations of African ancestry have lower osteoporotic fracture risk and higher BMD than other ethnic groups. However, there is a paucity of information regarding the genetic and environmental influences on bone health among populations of African heritage. MATERIALS AND METHODS: We dissected the genetic architecture of areal BMD measured by DXA at the proximal femur, lumbar spine, and whole body and volumetric BMD measured by pQCT at the distal and proximal radius and tibia in 283 women and 188 men > or =18 years of age (mean, 43 years) from eight multigenerational Afro-Caribbean families (mean family size > 50). Using quantitative genetic methods, we estimated the residual heritability and the effects of anthropometric, demographic, lifestyle, and medical variables on areal and volumetric BMD. RESULTS: Compared with U.S. non-Hispanic blacks and whites, areal BMD at the femoral neck was highest in the Afro-Caribbean men and women at all ages. Trabecular volumetric BMD decreased linearly with increasing age, whereas cortical volumetric BMD did not decrease until age 40-49, especially in women. Anthropometric, lifestyle, and medical factors accounted for 12-32% of the variation in areal and volumetric BMD, and residual heritabilities (range, 0.23-0.52) were similar to those reported in other ethnic groups. Heritability of cortical BMD was substantially lower than that of areal or trabecular volumetric BMD, although the measured covariates accounted for a similar proportion of the total phenotypic variation. CONCLUSIONS: Our study is the first comprehensive genetic epidemiologic analysis of volumetric BMD measured by QCT and the first analysis of these traits in extended families of African descent. Genes account for as much or more of the total variation in areal and volumetric BMD than do environmental factors, but these effects seem to differ for trabecular and cortical bone.     

Effect of aging on trabecular and compact bone components of proximal and ultradistal radius

Bone densitometry has become a major tool for osteoporosis risk assessment. The traditional dual-energy X-ray absorptiometry (DXA) methods are able to evaluate the bone mineral content (BMC; mg/cm) and the areal density (BMD; mg/cm²), but only quantitative computed tomography (QCT) has the potential to measure the true volumetric bone density in the sense of mass per unit volume (mg/cm³). Peripheral QCT (pQCT) measurements were carried out at the non-dominant radius using a Stratec XCT 960 (Unitrem, Roma) in 241 postmenopausal and 29 premenopausal women. The sites of evaluation were both the ultradistal and the proximal radius. The technique used has a coefficient of variation of 2% and it allows separation of the bone section into trabecular and cortical bone on the basis of density threshold. Bone mass of radius, hip and spine was also evaluated by DXA procedures. The bone density data obtained by pQCT were significantly correlated with all DXA measurements. The correlation coefficients between their respective BMD values ranged from 0.48 to 0.75, but for the BMC values of the radius the correlation coefficients ranged from 0.82 to 0.93. The BMD values measured by DXA, but not by pQCT, were positively related with patient heights. All pQCT density measurements, including those obtained at the proximal radius and containing exclusively cortical bone, where negatively related with age and years since menopause. A partial volume effect, which is increasingly relevant the thinner are the bone cortices, might explain that. However, by applying increasing density thresholds, cortical bone density seems to decrease with age as a consequence of a gradual density diminution from the inner part of the bone cortex outwards. Trabecular bone density decreases with aging, but its overall mass does not change as a consequence of an age-related enlargement of trabecular area. Thus, the proportion of trabecular bone over total bone rises, and this might be relevant for our understanding of the age-related changes in bone turnover and rate of bone loss.     

Comparison of DXA and MRI methods for interpreting femoral neck bone mineral density.

The aim of the study was to improve the practical implementation of the dual X-ray absorptiometry (DXA) by converting the areal bone mineral density BMD (BMD(areal)) to volumetric BMD using magnetic resonance (MR) imaging (MRI) because a failure to control for the femoral neck size can lead to erroneous interpretation of BMD values. We also evaluated the feasibility of MR T2* relaxation time in assessing bone mineral status of the femoral neck. Twenty-eight randomly selected 47- to 64-yr-old healthy men were studied. The men had neither unilateral nor bilateral hip osteoarthritis according to radiographs. Bone width, mineral content (BMC), BMD(areal), and apparent volumetric BMD (BMD(vol)) of the right femoral neck were measured with DXA. The BMD(vol) was calculated by approximating the femoral neck to be cylindrical with a circular cross-section (Vol(dxa)). Volumetric measurements from MR (Vol(mri)) images of the femoral neck were also used to create a BMD measure that was corrected for the femoral neck volume (BMD(mri)). T2* measurements were performed with a 1.5-T scanner (Siemens Magnetom 63SP, Erlangen, Germany). A single 10-mm-thick coronal slice was generated on the femur with a repetition time of 60 ms, and nine echo times (4-20 ms) were used to derive T2* values. Vol(mri) correlated positively (r = 0.828, p < 0.001) with Vol(dxa). However, the Vol(mri) of the femoral neck was 18% lower than the Vol(dxa). Similarly, the BMD(mri) was related to the BMD(vol) (r = 0.737, p < 0.001). Because of the difference in the volumetric measures, the BMD(mri) of the femoral neck was 21% higher than the BMD(vol) (p < 0.001). T2* relaxation time showed a significant negative correlation with BMC, BMD(areal), BMD(vol), and BMD(mri) (r = -0.423 to -0.757, p < 0.05-0.001). In conclusion, these results are evidence that DXA-derived volume approximations by the cylinder with circular cross-section geometry may lead to lower DXA-derived BMD(vol) values, as compared to true MRI-derived volumetric bone mineral density. Thus, the BMD(vol) may not be an accurate method to calculate the true volumetric BMD in the femoral neck. Our results also suggest that the MRI-derived T2* method may be used to approximate the BMD in the proximal femur.     

The effects of gonadectomy on bone size, mass, and volumetric density in growing rats are gender-, site-, and growth hormone-specific.

Peak volumetric bone mineral density (BMD) is determined by the growth in bone size relative to the mineral accrued within its periosteal envelope. Thus, reduced peak volumetric BMD may be the result of reduced mineral accrual relative to growth in bone size. Because sex steroids and growth hormone (GH) influence bone size and mass we asked: What are the effects of gonadectomy (Gx) on bone size, bone mineral content (BMC), areal and volumetric BMD in growing male and female rats? Does GH deficiency (GH-) reduce the amount of bone in the (smaller) bone, i.e., reduce volumetric BMD? Does GH- alter the effect of Gx on bone size and mineral accrual? Gx or sham surgery was performed at 6 weeks in GH- and GH replete (GH+) Fisher 344 male and female rats. Changes in bone size, volume, BMC, areal and volumetric BMD, measured using dual X-ray absorptiometry (DPX-L), were expressed as percentage of controls at 8 months (mean +/- SEM). All results shown were significant (p < 0.05 level) unless otherwise stated. In GH+ and GH- males, respectively, Gx was associated with: lower femur volume (24%, 25%), BMC (43%, 45%), areal BMD (21%, 14%), and volumetric BMD (30%, 28%); lower spine (L1-L3) volume (26%, 28%), BMC (26%, 30%), and areal BMD (28%, 12%), but not volumetric BMD. Following Gx, GH+ females had increased femur volume (11%), no effect on BMC, decreased areal BMD (6%) and decreased volumetric BMD (17%); GH- females had no change in femur volume, but decreased femur BMC (24%), areal BMD (10%), and volumetric BMD (25%). In GH+ and GH- females, respectively, Gx was associated with a decrease in spine (L1-L3) BMC (12%, 15%), areal BMD (16%, 15%), and volumetric BMD (10%, 16%) with no change in volume. Deficits in non-Gx GH- relative to non-Gx GH+ (males, females, respectively) were: femur BMC (49%, 37%), areal BMD (23%, 8%), volume (19%, 19%) and volumetric BMD (37%, 22%); spine (L1-L3) BMC (46%, 42%), areal BMD (37%, 43%), volume (10%, 15%), and volumetric BMD (40%, 33%). Testosterone and GH are growth promoting in growing male rats, producing independent effects on bone size and mass; deficiency produced smaller appendicular bones with reduced volumetric BMD because deficits in mass were greater than deficits in size. At the spine, the reduction in size and accrual were proportional, resulting in a smaller bone with normal volumetric BMD. In growing female rats, estrogen was growth limiting at appendicular sites; deficiency resulted in a GH-dependent increase in appendicular size, relatively reduced accrual, and so, reduced volumetric BMD in a bigger bone. At the spine, accrual was reduced while growth in size was normal, thus volumetric BMD was reduced in the normal sized bone. Understanding the pathogenesis of low volumetric BMD requires the study of the differing relative growth in size and mass of the axial and appendicular skeleton in the male and female and the regulators of the growth of these traits.     

Differentiating between orchiectomized rats and controls using measurements of trabecular bone density: A comparison among DXA,Histomorphometry, and peripheral quantitative computerized tomography

In studies of rat bone metabolism, trabecular bone density should be measured. Three established methods of measuring trabecular bone include trabecular bone volume by histomorphometry (BV/TV%), trabecular bone density by peripheral quantitative computerized tomography (pQCT), and areal bone density of trabecular-rich regions by dual x-ray absorptiometry (DXA). We compared the ability of these three methods to discriminate between orchiectomized (orchidectomized) rats and controls. Sixteen male Sprague-Dawley rats (400–425 g) were orchiectomized, and 16 others were controls. In vivo spine bone mineral density (BMD) was measured at the beginning of the study and again after 11 weeks. Rats were sacrificed, and ex vivo BMDs of the right femur and tibia were measured by DXA, followed by trabecular bone density of the right proximal tibia by pQCT. BV/TV% of the left proximal tibia was measured by histomorphometry. Differences between groups were detected by all three methods, but both the magnitude of the difference between groups and the variance of the measurements was much greater for histomorphometry and pQCT than for DXA. Consequently, the statistical significance for the difference between groups was comparable for all three methods. Of the sites measured with DXA, the proximal tibia had the greatest statistical significance for the difference between groups. In summary, all three methods can demonstrate the effect of orchiectomy on trabecular bone. The large differences between groups seen by histomorphometry are also seen by pQCT but not by DXA. We conclude that trabecular bone density by pQCT may be a reasonable surrogate for measurements by histomorphometry.Portions of the data presented here were presented at the 16th Annual Meeting of the American Society for Bone and Mineral Research, Kansas City, Missouri, September 30-September 9–13, 1994.