Videodensitometry of osteons in females with femoral neck fractures

Summary The medial femoral cortices of 10 females with femoral neck fractures and 10 age-matched female autopsy cases were studied using computer-assisted videodensitometry. Radiographic mineral density was determined using the calibration method described by Martin et al. [20]. Measurements were made of porosity, osteon and haversian canal dimensions, and of interstitial and osteon mineral density across the cortical wall of the orthopedic calcar region. There were no differences between the fracture and nonfracture groups in the overall mean mineral density of the bone averaged over the microstructure, excluding pore space, or in the interstitial bone mineral density. The porosity in the fracture group was greater than in the autopsy group, especially in the periosteal region, where the porosity was 2.4 times greater and where there were also 27% fewer osteons per unit area than in the autopsy group (P<0.05). Mean osteon mineral density was 2.5% higher in the fracture group (P<0.05) compared with the autopsy group in the endosteal region, and 4% higher in the periosteal region. Osteon and haversian canal areas were also larger in the fracture group, especially in the middle region of the cortical wall (17% and 23%, respectively, P<0.05). Presented at the Annual Meeting of the Orthopaedic Research Society, 17–20 February 1992     

Why would cement porosity reduction be clinically irrelevant, while experimental data show the contrary.

Laboratory bench tests have shown that porosity reduction increases the fatigue life of bone cement specimens. Clinically, however, the effect porosity reduction is subject to debate. We hypothesized that the discrepancy between clinical and experimental findings is related to differences in the stress distribution, which is typically uniform in experimental test specimens, while stress concentrations exist in cement around hip implants. We simulated fatigue failure of cement in a finite element model of an experimental test specimen and of a transverse slice of a total hip arthroplasty with a sharp-cornered stem. Four levels of porosity were introduced. In the fatigue test specimen model, the fatigue life clearly was dependent on the level of porosity, while in the transverse slice model, the level of porosity had virtually no effect on failure of the cement mantle. The results of the simulations confirmed our hypothesis. In simulations of laboratory tests, pores clearly acted as crack initiators, while in the simulation of a real total hip reconstruction, crack formation was governed by local stress singularities. This explains why the beneficial effect of cement porosity reduction on the lifetime of total hip reconstructions may be hard to detect clinically.     

多孔生物陶瓷与PVA水凝胶复合材料的制备与力学性能分析

目的将多孔生物陶瓷和聚乙烯醇(PVA)水凝胶交联成为一个仿生软骨-硬关节双层结构,并对该结构的微观形貌和力学性能进行分析。方法以羟基磷灰石(HA)为基体,采用添加碳酸氢铵(NH4HCO3)晶粒造孔的方式制备不同孔隙率的多孔羟基磷灰石生物陶瓷,以聚乙烯醇(PVA)为主要原料,环氧丙烷为交联剂,在多孔生物陶瓷表面及基体内交联制备出PVA水凝胶形成双层结构,对试样的断口形貌进行表征,对试样的拉伸强度和剪切强度等性能进行测试分析。结果交联的PVA水凝胶可以渗入到生物陶瓷基体表层以下的孔隙中,并且陶瓷基体和PVA水凝胶有很好的结合。随着多孔生物陶瓷孔隙率的增大,试样的最大拉伸和剪切负载均增大,平均孔隙率为70%试样的最大拉伸和剪切负载分别为153.61 N和64.46 N;而相应的拉伸和剪切强度略有下降,平均孔隙率为30%试样对应的最大拉伸和剪切强度分别为2.12 MPa和1.13 MPa。两者的失效形式均是因为裂纹的扩展,断口的微观形貌表明,断裂面存在明显的裂纹和内部缺陷,同时可观察出裂纹源和扩展方向。结论考虑到多孔生物陶瓷基体的强度,平均孔隙率为50%的多孔生物陶瓷的渗入效果适中,试样的拉伸强度和剪切强度、多孔生物陶瓷基体的压缩强度也有一定的保证,选择孔隙率为50%的试样较为合适。     

Swept-source optical coherence tomography as a new tool to evaluate defects of resin-based composite restorations

Objectives

Current diagnostic imaging modalities for resin-based composites (RBC) do not possess sufficient resolution and cross-sectional tomographic imaging to detect defects of RBC restorations in real-time. The purpose of this in vivo study was to investigate swept-source optical coherence tomography (SS-OCT) as a new tool to evaluate defects of RBC restorations.

Methods

We evaluated for the failure of RBC restorations in 52 patients (11 male, 41 female) at the Division of Oral and Dental Surgery, National Centre for Geriatrics and Gerontology, Japan. SS-OCT images of the 132 RBC restorations were obtained in order to investigate their marginal adaptation, porosity and internal integrity.

Results

Rates of defective restorations in terms of marginal adaptation, large porosity and gap formation were 65.2 percent, 27.3 percent, and 15.2 percent, respectively. Only 18.9 percent of the RBC restorations had no defects.

Conclusions

SS-OCT has the potential to provide higher-resolution information related to the structure of RBC restorations currently unavailable with any diagnostic or imaging method.     

Radial Anatomic Variation of Ultrasonic Velocity in Human Cortical Bone

Quantitative ultrasound techniques can be used to retrieve cortical bone quality. The aim of this study was to investigate the anatomic variations in speed of sound (SOS) in the radial direction of cortical bone tissue. SOS measurements were realized in 17 human cortical bone samples with a 3.5-MHz transverse transmission device. The radial dependence of SOS was investigated in a direction perpendicular to the periosteum. For each sample, bone porosity was measured using an X-ray micro-computed tomography device. The mean SOS was 3586 ± 255 m/s. For 16 of 17 specimens, similar radial variations in SOS were observed. In the periosteal region, SOS first decreased in the direction of the endosteum and reached a minimum value approximately in the middle of the cortical bone. SOS then increased, moving to the endosteal region. A significant negative correlation was obtained between SOS and porosity (R = –0.54, p = 0.02).     

Intrinsic porosity of calcium phosphate cements and its significance for drug delivery and tissue engineering applications

One key point in the field of tissue engineering and drug delivery is to provide materials with an adequate porosity. Many events, including nutrient and waste exchange in scaffolds for tissue engineering, as well as the drug-loading capacity and control of the release rate in drug delivery systems, are controlled by the size, shape and distribution of the pores in the material. Calcium phosphate cements (CPCs) possess an intrinsic porosity that is highly suited for these applications, and this porosity can be controlled by modifying some processing parameters. The objective of this work was to characterize and control the intrinsic porosity of α-tricalcium phosphate (α-TCP) cements, and to investigate its role against adsorption of bovine serum albumin (BSA). Cements with different percentages of open porosity (35–55%) were prepared by modifying the liquid-to-powder ratio. In addition, two different TCP particles were used to yield cements with specific surface areas of 20 and 37 m² g⁻¹. Mercury porosimetry analysis on the set cements showed in most cases a bimodal pore size distribution which varied with the processing parameters and affected differently the adsorption and penetration of BSA. The peak occurring at larger pore dimensions controlled the penetration of BSA and was ascribed to the voids generated in between crystal aggregates, while the peak appearing at lower pore sizes was believed to be due to the intercrystallite voids within aggregates. It was found that, at the concentrations studied, the high intrinsic porosity in CPC does not ensure protein penetration unless there is an adequate pore size distribution.     

The relationship between cement fatigue damage and implant surface finish in proximal femoral prostheses

The majority of cemented femoral hip replacements fail as a consequence of loosening. One design feature that may affect loosening rates is implant surface finish. To determine whether or not surface finish effects fatigue damage accumulation in a bone cement mantle, we developed an experimental model of the implanted proximal femur that allows visualisation of damage growth in the cement layer. Five matt surface and five polished surface stems were tested. Pre-load damage and damage after two million cycles was measured. Levels of pre-load (shrinkage) damage were the same for both matt and polished stems; furthermore damage for matt vs. polished stems was not significantly different after two million cycles. This was due to the large variability in damage accumulation rates. Finite element analysis showed that the stress is higher for the polished (assumed debonded) stem, and therefore we must conclude that either the magnitude of the stress increase is not enough to appreciably increase the damage accumulation rate or, alternatively, the polished stem does not debond immediately from the cement. Significantly (P=0.05) more damage was initiated in the lateral cement compared to the medial cement for both kinds of surface finish. It was concluded that, despite the higher cement stresses with debonded stems, polished prostheses do not provoke the damage accumulation failure scenario.     

Human vertebral bone: Relation of strength,porosity, and mineralization to fluoride content

Summary Radiographically normal vertebral bone cylinders from 80 male subjects were tested mechanically by static compression and analyzed for porosity, fluoride and ash content. As a group, they had low fluoride content, suggesting little prior intake, consonent with this geographic area. Nevertheless, increasing levels of fluoride were associated with bulkier bone, less porosity, and less mineral per unit of bone, which in direction though not degree suggested changes similar to those of osteomalacia and opposite from those of osteoporosis without apparent threshold. The higher fluoride hard tissue was weaker in static tests than that with less fluoride, but the increased bulk apparently offset this, resulting in bones of unchanged static strength. Hence, water fluoridation should not alter static bone strength. There has, however, been a recent report suggesting that increased mineralization of bone renders it more brittle and thus more likely to fracture on impact. Therefore, the possibility that fluoridation may increase impact resistance by lessening mineralization can be entertained.     

Superporous hydrogels for cartilage repair: Evaluation of the morphological and mechanical properties

Despite extensive research in the design of biomaterials for articular cartilage repair, there remains a need for the development of materials with the mechanical compliance to function synergistically with healthy cartilage, but porous enough to allow for tissue integration. In this study, superporous hydrogels of poly(vinyl alcohol) and poly(vinyl pyrrolidone) were prepared using a novel technique consisting of a double emulsion process. The hydrogel emulsions were physically cross-linked by freeze-thaw cycling. The hydrogels had a high degree of porosity, determined using environmental scanning electron microscopy, a technique superior to any method that involves dehydrating the samples. Increasing the volume of organic solvent increased porosity, due to cross-linking of the hydrogel solution around the droplets in the emulsion, leaving pores where the organic solvent was present. Poly(lactic-co-glyclic acid) microparticles formed and were embedded in the matrix. The mechanical properties, measured in confined creep and in unconfined, uniaxial compression, were similar to native articular cartilage. The permeability of the samples was unaffected by changing solvent content, despite changes in porosity. These materials are good candidates for tissue engineering of cartilage because they can mimic mature cartilage mechanically while providing a porous matrix through which cells can migrate and proliferate.     

酸碱处理多孔钛表面血清蛋白的吸附行为

目的研究酸碱处理后的多孔钛表面血清蛋白吸附行为。 方法采用粉末冶金法制备多孔钛材料,使用酸碱处理后制作酸碱处理多孔钛（AAPT）试件51个,同时制备未行酸碱处理多孔钛（NTPT）及致密钛（NTDT）试件各35个。采用扫描电镜（SEM）观察NTDT试件表面形貌,用表面接触角分析仪与全自动气体吸附仪测定三组的表面接触角和比表面积（SSA）。BCA法测定NTDT、NTPT及AAPT组试件不同时间的蛋白吸附量。采用单因素方差分析进行统计分析,LSD-t检验进行两两比较。 结果SEM显示NTDT表面光滑。AAPT组表面接触角（22.08°）显著小于NTPT组（93.7°）和NTDT组（75.69°）,差异有统计学意义（F= 392.02,P<0.001）。AAPT组SSA（27.05）均高于NTDT组（3.74）和NTPT组（18.36）,差异有统计学意义（F= 4586.10,P<0.001）。在各时间点,AAPT组吸附的蛋白质明显多于NTDT组和NTPT组（P<0.001）;AAPT、NTPT和NTDT组表面的蛋白吸附随着时间逐渐增加,最终达到稳定。 结论酸碱处理后的多孔钛可显著提高材料表面的血清蛋白吸附量。