Porous Titanium‐6 Aluminum‐4 Vanadium Cage Has Better Osseointegration and Less Micromotion Than a Poly‐Ether‐Ether‐Ketone Cage in Sheep Vertebral Fusion

Interbody fusion cages made of poly‐ether‐ether‐ketone (PEEK) have been widely used in clinics for spinal disorders treatment; however, they do not integrate well with surrounding bone tissue. Ti‐6Al‐4V (Ti) has demonstrated greater osteoconductivity than PEEK, but the traditional Ti cage is generally limited by its much greater elastic modulus (110 GPa) than natural bone (0.05–30 GPa). In this study, we developed a porous Ti cage using electron beam melting (EBM) technique to reduce its elastic modulus and compared its spinal fusion efficacy with a PEEK cage in a preclinical sheep anterior cervical fusion model. A porous Ti cage possesses a fully interconnected porous structure (porosity: 68 ± 5.3%; pore size: 710 ± 42 μm) and a similar Young's modulus as natural bone (2.5 ± 0.2 GPa). When implanted in vivo, the porous Ti cage promoted fast bone ingrowth, achieving similar bone volume fraction at 6 months as the PEEK cage without autograft transplantation. Moreover, it promoted better osteointegration with higher degree (2‐10x) of bone‐material binding, demonstrated by histomorphometrical analysis, and significantly higher mechanical stability (P < 0.01), shown by biomechanical testing. The porous Ti cage fabricated by EBM could achieve fast bone ingrowth. In addition, it had better osseointegration and superior mechanical stability than the conventional PEEK cage, demonstrating great potential for clinical application.     

Aluminum-induced neo-osteogenesis: a generalized process affecting trabecular networking in the axial skeleton

To determine if aluminum-induced neo-osteogenesis occurs in the axial skeleton, we compared spinal bone density and vertebral histology of beagles treated with aluminum for 8 and 16 weeks to that of untreated normals. Administration of aluminum (1.25 mg/kg) did not alter serum calcium, phosphorus, or creatinine but did result in a significant elevation of vertebral bone density, measured by quantitative computed tomography, after both 8 (286.7 +/- 12.4 mg/ml) and 16 (361.7 +/- 46.5 mg/ml) weeks of treatment compared with controls (212.2 +/- 4.5 mg/ml). In accord with the increased bone density, biopsies from the spine displayed evidence of neo-osteogenesis, including the presence of woven bone, both mineralized and unmineralized, within the marrow space. The genesis of such woven bone units resulted after 16 weeks in a significant increase in trabecular bone volume, woven and lamellar (51.2 +/- 4.4 versus 32.4 +/- 1.2%; p less than 0.05), woven bone volume (9.1 +/- 3.6 versus 0 +/- 0%; p less than 0.05), and trabecular number (4.5 +/- 0.3 versus 3.5 +/- 0.2 per mm; p less than 0.05). In addition, scanning electron microscopic evaluation of the bone biopsies confirmed the existence of new trabecular plates that provided interconnections between existent units. These observations illustrate that aluminum-induced neo-osteogenesis positively influences trabecular networking in the axial skeleton. Such enhancement of bone histogenesis contrasts with the effects of other pharmacologic agents that solely alter the thickness of existing trabecular plates or rods within the vertebral spongiosa.     

Variations in the individual thick lamellar properties within osteons by nanoindentation.

The nanoindentation method was used to examine variations in the individual thick lamellar properties within completed secondary osteons as a function of distance from the osteonal center (haversian canal). In general, there is a decline in both elastic modulus and hardness from the center of the osteon outward. Because some of the osteons may have a different general trend than others, an analysis of covariance was also carried out. The overall analysis was highly significant for both elastic modulus and hardness. Also, osteon number was significant as a factor, indicating that there was some difference in the overall thick lamellar properties of the different osteons. An unpaired t-test showed statistically significant differences (p = 0.0005 and 0.0004, respectively) between thick lamellar properties obtained from most of the inner two osteonal lamellae (E = 20.8 +/- 1.3 GPa and H = 0.65 +/- 0.06 GPa) and those from outermost two osteonal lamellae (E = 18.8 +/- 1.0 GPa and H = 0.55 +/- 0.05 GPa). In general, lamellar properties from near to the center of the osteon were greater than those from the outermost osteonal lamella. The mechanical properties of osteons are also significantly lower than those of the interstitial bone (p < 0.0001). The ratio (E1/E2) of the elastic moduli of the outermost osteonal lamella (E1) (considered to be the soft part of the osteons) and that of interstitial bone (E2) was approximately 0.7. These results may have important implications for the mechanical contribution of individual osteons to bone biomechanics.     

In vitro acoustic waves propagation in human and bovine cancellous bone.

The acoustic behavior of cancellous bone with regard to its complex poroelastic nature has been investigated. The existence of two longitudinal modes of propagation is demonstrated in both bovine and human cancellous bone. Failure to take into account the presence of these two waves may result in inaccurate material characterization. INTRODUCTION: Acoustic wave propagation is now a commonly used nondestructive method for cancellous bone characterization. However, wave propagation in this material may be affected by fluid-solid interactions inherent to its poroelastic nature, resulting in two different longitudinal waves. This phenomenon has been demonstrated in previous studies and is in agreement with Biot's theory. The purpose of this paper is to extend these findings to human trabecular bone and to thoroughly investigate these two waves. MATERIALS AND METHODS: Sixty human and 14 bovine cancellous bone cubic specimens were tested in vitro in three different directions using an immersion acoustic transmission method. Original procedures were developed to quantify both velocity and attenuation characteristics of each wave. In term of attenuation, a modified broadband ultrasound attenuation (BUA), describing the rate of change of the frequency-dependent attenuation, was defined for each wave (FDUA). RESULTS: Both waves were identified in most of the specimens. The fast wave velocities demonstrated a negative linear correlation with porosity (1500-2300 m/s, R2 = 0.44, p < 10(-3)), whereas the slow wave velocities exhibited two different behaviors: (1) a first set of data clearly dependent on porosity showing a positive linear correlation (1150-1450 m/s, R2 = 0.26, p < 10(-3)) and (2) a second group independent on porosity. The fast wave FDUA (20-140 dB/cmMHz) showed a parabolic behavior and reached a maximum for 75% porosity (second degree relationship R2 = 0.41,p < 10(-3)), whereas a positive linear behavior was observed for the slow wave FDUA (15-40 dB/cmMHz; R2 = 0.15, p < 10(-2)). CONCLUSIONS: Existence of two wave propagation modes were demonstrated in human cancellous bone. Our data suggest that, in some cases, the amplitude of the slow wave is much larger than the amplitude of the fast wave. For this reason, care should be taken when using measurement systems that incorporate simple threshold detection because the fast wave could remain undetected. Moreover, failure to consider the presence of these two waves could result in an inaccurate quantification of cancellous bone physical properties.     

The effects of metabolic acidosis on bone formation and bone resorption in the rat

Metabolic acidosis (MA) has been implicated in the pathogenesis of both osteomalacia and osteopenia. Alterations in the secretion of parathyroid hormone and in the metabolism of vitamin D may contribute to such skeletal changes. To minimize the influence of these factors, quantitative bone histology and measurements of bone formation using double tetracycline labeling were done in thyroparathyroidectomized (TPTX) rats with MA induced by ammonium chloride (TPTX-A), and in both non-acidotic TPTX (TPTX-C) and intact (C) controls. To evaluate the response of both cortical and trabecular bone to MA, histologic studies were done at three separate sites in the tibia, cortical bone from the mid-shaft, and trabecular bone from the epiphysis and from the metaphysis. Plasma pH was lower in TPTX-A, 7.24 +/- 0.10, than in either TPTX-C, 7.39 +/- 0.03, or C, 7.43 +/- 0.04, P less than 0.01, and urinary hydroxyproline excretion increased from 89.8 +/- 8.7 in TPTX-C to 150.2 +/- 25.9 micrograms/mg/creatinine in TPTX-A, P less than 0.01. Resorption surface at the epiphysis increased from 1.8 +/- 0.6% in TPTX-C to 4.0 +/- 1.6% in TPTX-A, P less than 0.05, values not different from those in C, 3.1 +/- 1.1%. Resorption surface was unchanged at other skeletal sites, but total bone volume at the metaphysis fell from 15.5 +/- 5.6% in TPTX-C to 9.0 +/- 4.3% in TPTX-A, P less than 0.05. Bone formation was reduced at each skeletal site in TPTX-A vs. TPTX-C, P less than 0.05 for all values, but histologic evidence of osteomalacia was not observed.(ABSTRACT TRUNCATED AT 250 WORDS)     

A comparison of radial peripheral quantitative computed tomography, calcaneal ultrasound, and axial dual energy X-ray absorptiometry measurements in women aged 45-55 yr.

Perimenopausal bone loss is considered to affect trabecular bone preferentially. Peripheral quantitative computed tomography (pQCT) quantifies trabecular bone mineral density (BMD) independently at the ultradistal radius. This article examines differences in pQCT BMD between late premenopausal and early postmenopausal women, comparing the differences with calcaneal ultrasound and axial dual energy X-ray absorptiometry measurements. One hundred nineteen normal perimenopausal women aged 45-55 yr who attended a randomized osteoporosis screening program were stratified by menopausal status into premenopausal (PRE: n = 79) and postmenopausal (POST: n = 40) groups. All measurements were lower in the postmenopausal group with the exception of ultrasonic velocity (PRE vs POST: 1397 +/- 53.8 vs 1421 +/- 58.5 m/s, p = 0.037). Total (391.8 +/- 52.9 vs 366.3 +/- 68.6 g/cm(3), p = 0.013) and subcortical (533.6 +/- 59.4 vs 504.3 +/- 79.8 g/cm(3) p = 0.018), but not trabecular (187.5 +/- 38.8 vs 173.2 +/- 46.6 g/cm(3), p = 0. 098) or cortical (561 +/- 53.4 vs 551.2 +/- 66 g/cm(3), p = 0.174), pQCT BMD measurements were significantly lower in the POST group, as were ultrasonic attenuation (79.4 +/- 16 vs 72.3 +/- 18.0 dB/Mz, p = 0.034), DXA spine (1.032 +/-16 vs 0.959 +/- 0.2 g/cm(2), p = 0.003), and all hip (p 相似文献   

Genetic regulation of cortical and trabecular bone strength and microstructure in inbred strains of mice.

The inbred strains of mice C57BL/6J (B6) and C3H/HeJ (C3H) have very different femoral peak bone densities and may serve as models for studying the genetic regulation of bone mass. Our objective was to further define the bone biomechanics and microstructure of these two inbred strains. Microarchitecture of the proximal femur, femoral midshaft, and lumbar vertebrae were evaluated in three dimensions using microcomputed tomography (microCT) with an isotropic voxel size of 17 microm. Mineralization of the distal femur was determined using quantitative back-scatter electron (BSE) imaging. MicroCT images suggested that C3H mice had thicker femoral and vertebral cortices compared with B6. The C3H bone tissue also was more highly mineralized. However, C3H mice had few trabeculae in the vertebral bodies, femoral neck, and greater trochanter. The trabecular number (Tb.N) in the C3H vertebral bodies was about half of that in B6 vertebrae (2.8(-1) +/- 0.1 mm(-1) vs. 5.1(-1) +/- 0.2 mm(-1); p < 0.0001). The thick, more highly mineralized femoral cortex of C3H mice resulted in greater bending strength of the femoral diaphysis (62.1 +/- 1.2N vs. 27.4 +/- 0.5N, p < 0.0001). In contrast, strengths of the lumbar vertebra were not significantly different between inbred strains (p = 0.5), presumably because the thicker cortices were combined with inferior trabecular structure in the vertebrae of C3H mice. These results indicate that C3H mice benefit from alleles that enhance femoral strength but paradoxically are deficient in trabecular bone structure in the lumbar vertebrae.     

Trabecular architecture in women and men of similar bone mass with and without vertebral fracture: II. Three-dimensional histology

We recently developed a simple and inexpensive method that complements established bone histomorphometry procedures by enabling the two-dimensional imaging of cancellous bone to be viewed within its three-dimensional context with the marrow tissue in place and without detriment to the material for other histological purposes. The method, based on the preparation and superficial staining of slices 300 microm thick, enables "real" (i.e., unstained) trabecular termini to be separated from "artifactual" (i.e., stained) termini, providing a direct measure of cancellous connectivity in osteopenic bone. The technique was applied to osteopenic age-matched, white, postmenopausal women (31 with and 22 without vertebral compression fractures) with a similar bone status, as measured at the spine by absorptiometry and at the iliac crest by histology (see part I of this study). Despite the similarity in the mass of trabecular bone at either site, the results showed a significant difference (p < 0. 05) in the number of "real" trabecular termini between the groups, such that the fracture group had almost four times as many termini (mean +/- SE: 1.98 +/- 0.51/30 mm(2)) at the iliac crest as the nonfracture group (mean +/- SE: 0.53 +/- 0.31/30 mm(2)). Previous histomorphometry of the same material failed to detect a structural distinction between the two groups using established variables. It was concluded that a mass-independent trabecular discontinuity contributes to skeletal failure and that determination of the number of "real" disconnections (i.e., unstained termini) by the direct method proposed may provide a more sensitive discriminant of fracture than the present indirect procedures. A group of fracture and nonfracture men (see part I) suggested a similar distinction (fracture: 0.69 +/- 0.30/30 mm(2); nonfracture: 0.18 +/- 0.18/30 mm(2)), although the difference was not significant.     

人股骨头坏死微观结构及成骨、破骨细胞活性的区域性分布特征

 目的 比较人股骨头坏死标本不同区域的骨微观结构及成、破骨细胞活性。方法 收集2011年3月至2013年5月行全髋关节置换的非创伤性股骨头坏死患者术后的股骨头标本10例（Ficat Ⅳ期）,男6例,女4例;年龄40～57岁,平均47.7岁。Micro-CT扫描后,根据影像学识别骨质密度不同,将每个标本分为软骨下骨区、坏死区、硬化区、健康区,通过病理学检测、纳米压痕、实时荧光定量PCR、免疫组化染色等方法对不同区域的骨微观结构、微观力学性能及成骨、破骨细胞活性进行比较。结果 Micro-CT结果显示,股骨头坏死标本软骨下骨区及坏死区的骨小梁连续性破坏;硬化区的骨小梁数目增多,间隙变窄;正常区域骨小梁结构完整,厚度分布均匀。软骨下骨区、坏死区、硬化区和健康区骨小梁的弹性模量分别为（13.808±4.22） GPa、（13.999±3.816） GPa、（17.266±3.533） GPa和（11.927±1.743） GPa;硬度分别为（0.425±0.173） GPa、（0.331±0.173） GPa、（0.661±0.208） GPa和（0.423±0.088） GPa。抗酒石酸酸性磷酸酶（Trap）染色结果显示,软骨下骨区和坏死区可见Trap染色阳性细胞,硬化区及健康区未见Trap染色阳性细胞。免疫组化染色结果显示,骨形成相关因子Runx2和BMP2在硬化区及健康区表达高于其他区域;骨吸收相关因子RANK和RANKL在软骨下骨区及坏死区表达高于其他区域。结论 股骨头坏死塌陷过程中,骨微观结构发生明显改变,而坏死区骨小梁微观力学强度较健康区无显著降低。股骨头坏死标本中软骨下骨区及坏死区破骨细胞活性增强,硬化区成骨细胞活性增强。     

Analysis of bone ingrowth on a tantalum cup

Background:

Trabecular Metal (TM) is a new highly porous material made of tantalum (Zimmer, Warsaw, Indiana, USA). Its three-dimensional structure is composed of a series of interconnected dodecahedron pores that are on average 550 μm in diameter. This size is considered optimal for bone ingrowth and is similar to trabecular bone. The elastic modulus of TM (3 GPa) is more similar to that of cancellous (0,1-1,5 GPa) or cortical (112-18 GPa) bone and is significantly less similar to that of Titanium (110 GPa) and Co-Cr alloys (220 GPa). These features enable bone apposition and remodeling. The purpose of the present study was to evaluate the histology of the bone-implant interface in a human specimen.

Materials and Methods:

A highly porous tantalum cup (Zimmer, Warsaw, Indiana, USA) was removed for recurrent dislocations three years after implantation. In order to obtain a slice of the cup, two cuts were made on the centre using an Exakt cutting machine. Then the slice was embedded in a Technovit resin and a Hematoxylin-eosin stain was used to study the bone tissue. Bone ingrowth was calculated using a method based on simple calculations of planar geometry.

Results:

The histological evaluation of the periprosthetic tissues revealed a typical chronic inflammation with few particles of polyethylene that were birefringent using polarized light. The quantitative evaluation of bone ingrowth revealed that more than 95% of voids were filled with bone.

Discussion:

In the literature, a lot of studies focused on tantalum were carried on animal model. Up to now little information is available about the histology of the bone-tantalum interface in a human artificial joint. We had an opportunity to remove a well integrated cup hence this study. The histology confirmed the strong relationship between the structure of this material and bone. The morphometric analysis revealed a high percentage of bone ingrowth.     

退行性关节炎与骨质疏松性股骨颈骨小梁的有限元分析

目的以生物力学的观点探讨分析退行性关节炎(OA)及骨质疏松(OP)的临床病变表现。方法建立OA及OP患者股骨颈骨小梁的有限元模型,分别计算指标参数,并利用骨小梁分布密度,配合有限元法计算得到骨小梁组织真正的材料性质,重新模拟破坏的情形,观察不同模型的应变分布,并探讨各指标参数及材料性质对骨小梁强度的影响。结果骨小梁的数量越多、密度越高,达到屈服应变的比例就越低。骨小梁的间隔越大,则达到屈服应变的比例就越高。而骨小梁的表面积比及厚度与结构强度无关。试件的结构刚度、剪切模量及骨小梁组织的弹性模量等材料性质越高,其达到屈服应变的元素的比例就会越低。结论虽然几何外形也是影响材料性质的因素之一,但材料性质对骨小梁强度的影响要比几何外形明显。     

Uniaxial yield strains for bovine trabecular bone are isotropic and asymmetric.

Although evidence suggests that yield strains for trabecular bone are isotropic, i.e., independent of loading direction, decisive support for this hypothesis has remained elusive. To explicitly test whether yield strains for trabecular bone are isotropic, compressive and tensile yield strains of 51 specimens of bovine tibial trabecular bone (0.41 +/- 0.08 g/cm3 [mean apparent density +/- SD]) were measured without end artifacts in on-axis (along the principal trabecular orientation) and off-axis (30-40 degrees oblique to on-axis) orientations. Yield strains for the on-axis and off-axis orientations were similar in tension (0.80 +/- 0.03% compared with 0.85 +/- 0.04%, p = 0.21) and compression (0.97 +/- 0.05% compared with 0.96 +/- 0.07%, p > 0.99); as expected, modulus and strength depended on loading direction. When considered with an ancillary experiment on bovine tibial trabecular bone that showed yield strains to be similar between on-axis and 90 degrees off-axis bone, these results firmly establish the isotropy of uniaxial yield strains for bovine tibial trabecular bone. This bone is of high density and has a strong, plate-type, anisotropic architecture. Therefore, yield strains for uniaxial loading are expected to be isotropic, or nearly so, for other types of dense trabecular bone, although further work is required to confirm this and to establish this behavior for bone of lower density.     

Elderly recipients of hepatitis C positive renal allografts can quickly develop liver disease

Our institution explored using allografts from donors with Hepatitis C virus (HCV) for elderly renal transplantation (RT). Thirteen HCV- elderly recipients were transplanted with HCV+ allografts (eD+/R-) between January 2003 and April 2009. Ninety HCV- elderly recipients of HCV- allografts (eD-/R-), eight HCV+ recipients of HCV+ allografts (D+/R+) and thirteen HCV+ recipients of HCV- allografts (D-/R+) were also transplanted. Median follow-up was 1.5 (range 0.8-5) years. Seven eD+/R- developed a positive HCV viral load and six had elevated liver transaminases with evidence of hepatitis on biopsy. Overall, eD+/R- survival was 46% while the eD-/R- survival was 85% (P = 0.003). Seven eD+/R- died during follow-up. Causes included multi-organ failure and sepsis (n = 4), cancer (n = 1), failure-to-thrive (n = 1) and surgical complications (n = 1). One eD+/R- died from causes directly related to HCV infection. In conclusion, multiple eD+/R- quickly developed HCV-related liver disease and infections were a frequent cause of morbidity and mortality.     

Assessment by reflection ultrasound method of the effect of intermittent slow-release sodium fluoride-calcium citrate therapy on material strength of bone

It has been suggested that fluoride therapy, while increasing bone mass, produces bone with inferior mechanical properties. In the present report this hypothesis was tested using a novel reflection ultrasound technique. Transiliac crest bone biopsies were obtained from 16 patients with osteoporosis and vertebral compression fractures (12 women and 4 men, mean age 56 years) before and after approximately 2 years of intermittent slow-release sodium fluoride therapy (25 mg twice a day) combined with continuous calcium citrate supplementation. Samples were analyzed by a reflection ultrasound method, which analyzes ultrasound velocity with a sample site resolution of 200 microns and thus provides a measure of the mechanical property of single trabeculae (material). For the group, mean fractional change in velocity increased 6.1 +/- 2.3% (SEM) from a mean value of 3303 +/- 80 to 3484 +/- 55 m/s (p = 0.028). A total of 13 patients (81%) demonstrated higher velocities after treatment. Thus reflection ultrasound analysis of bone appears to provide a sensitive means of assessing changes in the material property of bone. Furthermore, these results suggest that the treatment regimen utilized in these patients improves strength of bone at the material or trabecular level largely independently of change in bone mass. The combination therapy also increased spinal (L2-L4) bone density for the group as assessed by dual-photon absorptiometry (5.3 +/- 2.0%). There was no significant correlation between the change in ultrasound velocity and bone density (r = 0.0026, p = 0.996).(ABSTRACT TRUNCATED AT 250 WORDS)     

Microindentation can discriminate between damaged and intact human bone tissue

Bone mineral density and microarchitecture was found to predict 70-95% of bone strength. Microdamage, as factor of bone quality, might help to explain the remaining uncertainties. The goal of this study was to investigate whether microindentation can discriminate between intact and severely damaged human vertebral bone tissue in vitro. One portion from each human vertebral slice (N=35) tested in compression in a previous study was embedded, polished and tested in wet conditions by means of microindentation. The indentation moduli and hardness (HV) of trabecular, osteonal and interstitial bone structural units were computed along the cranio-caudal direction. Each indented region was defined as damaged or intact as seen under a light microscope. A total of 1190 indentations were performed. While both hardness and indentation modulus were independent from gender, both mechanical properties were affected by damage and microstructure. The damaged regions showed 50% lower stiffness and hardness compared to undamaged ones. Interstitial bone was stiffer and harder (13.2±4.4 GPa and 44.7±20.3 HV) than osteonal bone (10.9±3.8 GPa and 37.8±17.3 HV), which was stiffer and harder than trabecular bone (8.1±3.0 GPa and 28.8±11.2 HV) indented in the transverse direction. Moreover, along the axial direction intact trabecular bone (11.4±4.3 GPa) was 16% less stiff than the intact interstitial bone and as stiff as intact osteonal bone. In conclusion microindentation was found to discriminate between highly damaged and intact tissue in both trabecular and cortical bone tested in vitro. It remains to be investigated whether this technique would be able to detect also the damage, which is induced by physiological load in vivo.     

Histomorphometric evidence for increased bone turnover without change in cortical thickness or porosity after 2 years of cyclical hPTH(1-34) therapy in women with severe osteoporosis

Parathyroid hormone (PTH) increases trabecular but may decrease cortical bone mass during treatment of postmenopausal osteoporosis. In a 2-year trial, PTH, with or without sequential calcitonin (CT), was given to 29 osteoporotic women (mean age 67 +/- 7 years), in 3-month cycles [28 days hPTH(1-34), 50 microg/day, +/-42 days CT, 75 units/day, 20 days "free"]. Over 2 years, lumbar spine bone mineral density measurements increased an average of 10%. Paired iliac crest biopsies were obtained 28 days and 2 years after starting the trial. The addition of CT made no difference to changes seen with cyclical PTH alone. Thus, the histomorphometric analyses for all 29 treated patients were compared with a separate group of biopsies from untreated osteoporotic control patients (n = 15). No significant increments in total bone volume or trabecular architecture were seen over 2 years of cyclical PTH treatment, although the light microscopic appearance of bone was normal. At the level of the bone remodeling unit, a twofold increase in total trabecular erosion surface over the control measurements was observed within the first 28 days of PTH treatment (10 +/- 5 vs. 5 +/- 3% trabecular surface, p < 0.01), which was sustained over 2 years. Trabecular bone formation rates (surface referent) were 11 +/- 7 microm(3)/microm(2)/year in control patients and threefold higher in treated patients both acutely (31 +/- 31 microm(3)/microm(2)/year, p < 0.01) and after 2 years (33 +/- 43 microm(3)/microm(2)/year, p < 0. 05). The activation frequency of trabecular remodeling was threefold higher than controls through 2 years of treatment (p < 0.05). The mean wall thickness of completed osteons after 2 years of treatment was significantly larger than controls (28 +/- 7 vs. 22 +/- 5 microm, p < 0.01), suggesting a positive remodeling balance, as well as the histomorphometric evidence of increased bone turnover and the increased resorption surfaces. Over 2 years of cyclical PTH therapy, cortical thickness remained significantly higher than controls (680 +/- 202 vs 552 +/- 218 microm, p < 0.05), without significant changes in cortical porosity. Thus, the histomorphometric changes during cyclical PTH therapy in patients with severe osteoporosis are consistent with increased trabecular bone turnover and a positive remodeling balance, with no evidence for detrimental changes in cortical bone.     

Trabecular bone architecture in female renal allograft recipients-- assessed by computed tomography

BACKGROUND: Osteopenia with decreased bone mineral density (BMD) is a frequent finding in renal allograft recipients. Data concerning the bone architecture in these patients do not exist, however. METHODS: We compared the bone architecture of 33 randomly assigned women (age 49 +/- 12 years), who had received renal allografts 5.6 +/- 5.3 years before the investigation, with 74 women (age 50 +/- 14 years) who were admitted for osteodensitometry. All patients underwent single-energy computed tomography (SEQCT) and a midvertebral high-resolution tomography with computer-assisted analysis of the trabecular vertebral body architecture. RESULTS: Progressive alteration of bone architecture was associated with increasing vertebral height loss of the vertebral body. Height reduction of a vertebral body of more than 15% was associated with a significantly lower BMD (-2.3 +/- 0.8 versus -1.1 +/- 1.1 standard deviations below normal BMD), a lower trabecular bone area (13 +/- 8% versus 42 +/- 22%) and a lower trabecular diameter (1.4 +/- 0.5 mm versus 2.2 +/- 0.8 mm) compared to recipients without height reduction. In comparison to a matched group of patients with similarly reduced BMD (1.1 +/- 1.2 versus 1.2 +/- 1.1 SD below normal BMD), renal allograft recipients showed a lower number of trabecular plates (5.6 +/- 3.1 versus 7.0 +/- 3.7) and a smaller intertrabecular surface (54 +/- 116 mm versus 75 +/- 138 mm). CONCLUSIONS: Alterations of bone architecture in renal allograft recipients were associated with progressive vertebral height loss. Despite similar bone mineral density, differences of bone architecture could be observed between renal allograft recipients and patients with osteoporosis.      

The proportion of trabecular bone in human vertebrae

The proportion of trabecular bone in human cadaver vertebrae was assessed by anatomic dissection. Thirty-two whole thoracic and lumbar vertebrae were obtained from 10 normal human postmenopausal female cadavers, 14 from 4 normal adult human male cadavers of similar age, and 8 from one female osteoporotic cadaver. Each vertebra was opened by saw cuts and separated into four tissue types: (1) body trabecular bone and marrow; (2) body cortical bone; (3) vertebral arch trabecular bone and marrow; and (4) vertebral arch cortical bone. Calcium was determined in each tissue type for each vertebra by ashing and atomic absorption spectrophotometry. Trabeculae accounted for 24.4 +/- 4.5% of the total calcium in whole female vertebrae, and 18.8 +/- 4.4% in whole male vertebrae (p less than 0.001). The body averaged 41.8% trabecular bone in females and 33.5% in males. The arch averaged 9.7% trabecular bone in females and 4.9% in males. The proportion of trabecular bone in the whole vertebrae in the single osteoporotic spine was 28.5 +/- 3.2%, a value not significantly different from the trabecular fraction in normal females. These data indicate that whole human thoraco-lumbar vertebrae are composed of a substantially lower proportion of trabecular bone than is usually assumed, and they suggest that cortical and trabecular bone are eventually lost in equal proportion from the vertebrae during the development of spinal osteoporosis. These results are important for the interpretation of data from noninvasive bone measurement techniques that evaluate the spine, and they suggest that studies of this type are important for any site where noninvasive bone mass measurement is done.     

Trabecular architecture in women and men of similar bone mass with and without vertebral fracture: I. Two-dimensional histology

While osteoporosis is characterized by a low bone mass there is a well-recognized overlap in bone mineral density (BMD) measurements between groups of subjects with and without vertebral fracture. To investigate whether differences in trabecular architecture may contribute to the presence or absence of fractures independent of the bone mass, fracture and nonfracture groups matched for age, gender, and BMD were assembled. Transiliac biopsies and corresponding lumbar spine BMD measurements from 31 women and 16 men with vertebral fracture were compared with those from 22 women and 11 men without fracture. Lumbar BMD (L1-4) was measured using a Hologic 2000 densitometer. The lumbar BMD was similar in women with and without fracture (0.63 g/cm(3) +/- 0.10 SD and 0.71 g/cm(3) +/- 0.17 SD, n.s.) and in men with and without fracture (0.72 g/cm(3) +/- 0.12 SD and 0.76 g/cm(3) +/- 0.17 SD, n.s.). Undecalcified iliac crest biopsy sections, 8 microm thick, were analyzed for remodeling variables and trabecular architecture using OsteoMeasure and TAS image analysis systems. No significant difference was found in either gender between fracture and nonfracture groups in percent bone volume (mean 10% in all groups), or in the wide range of remodeling and architectural variables measured, including the trabecular width, number, and separation, mean trabecular plate density and fractal dimension, as well as several indirect indices of connectivity including the node:terminus ratio, marrow star volume, and trabecular pattern factor. On the basis of this evidence it was concluded that there is no difference in the trabecular architecture between patients with crush fracture and controls when account is taken of bone mass. This suggests that microanatomical disruption is a predictable intrinsic feature of bone loss. However, there remains the possibility that the two-dimensional character of the structural deterioration measured indirectly is not sufficiently sensitive for the complex cancellous system. This is considered further in part II.     

Bone repair using a new injectable self-crosslinkable bone substitute.

A new injectable and self-crosslinkable bone substitute (IBS2) was developed for filling bone defects. The IBS2 consisted of a chemically modified polymer solution mixed with biphasic calcium phosphate (BCP) ceramic particles. The polymer hydroxypropylmethyl cellulose was functionalized with silanol groups (Si-HPMC) and formed a viscous solution (3 wt %) in alkaline medium. With a decrease in pH, self-hardening occurred due to the formation of intermolecular -Si-O- bonds. During setting, BCP particles, 40 to 80 microm in diameter, were added to the polymer solution at a weight ratio of 50/50. The resulting injectable material was bilaterally implanted into critically sized bone defects at the distal femoral epiphyses of nine New Zealand White rabbits. The IBS2 filled the bone defects entirely and remained in place. After 8 weeks, bone had grown centripetally and progressed towards the center of the defects. Newly formed bone, ceramic, and nonmineralized tissue ratios were 24.6% +/- 5.6%, 21.6% +/- 5.8%, and 53.7% +/- 0.1%, respectively. Mineralized and mature bone was observed between and in contact with the BCP particles. The bone/ceramic apposition was 73.4% +/- 10.6%. The yield strength for the IBS2-filled defects was 16.4 +/- 7.2 MPa, significantly higher than for the host trabecular bone tissue (2.7 +/- 0.4 MPa). This study showed that BCP particles supported the bone healing process by osteoconduction while the Si-HPMC hydrogel created intergranular space for bone ingrowth. This new injectable and self-crosslinkable bone substitute could be used conveniently in orthopedic surgery for filling critical-size bone defects.