Festigkeitsuntersuchungen an Pins aus humaner Femurkortikalis

For biomechanical evaluation of cortical bone as a potential source for internal fixation devices, pins of 2 and 3 mm in diameter were made from fresh human femora and subjected to bending loads. Some of the pins were tested without further treatment; others were defatted and dried in acetone solution. Of the acetone-treated pins, some were autoclaved either at 121 degrees C for 20 min or at 134 degrees C for 8 min. Acetone treatment of the pins caused a 5.5% increase in bending strength (p < or = 0.05) and a 6.6% increase in the elastic modulus (p < or = 0.05). The mean bending strength of the acetone-treated pins was 257 +/- 52 N/mm2 and the mean elastic modulus was 18,346 +/- 1292 N/mm2. Autoclaving of the pins at the lower temperature for a longer time led to a decrease in the bending strength of up to 16% and at the higher temperature for a shorter time to a decrease of up to 41%. To compare the strengths of the cortical and synthetic pins, 2-mm Biofix pins were also tested. The Biofix pins showed a 25% higher bending strength than the acetone-treated pins but a 12.5% lower elastic modulus. It should be noted that in animal studies the synthetic Biofix pins showed a 20% loss of strength within 2 days after implantation in situ.     

Mechanical properties of bone fixation devices prepared from a human allogenic bone

BACKGROUND: The major goal of the study was to create a novel, internal fixation devices based on human cortical bone for use in the orthopedic surgery. Because the biological properties of processed tissue have already been intensively studied, it was mandatory to evaluate the mechanical properties of our new products before introduction into clinical use. MATERIALS AND METHODS: Pins and screws of different diameters were formed from processed human lower limb bones prepared according to standard tissue banking procedures: freezing, de-fatting and radiation sterilization (35 kGy). The mechanical properties of the pins and screws were evaluated using bending or braking tests. RESULTS: The results indicate potential usefulness for clinical applications.     

同种异体皮质骨板移植治疗股骨假体周围骨折

目的 评价同种异体皮质骨板移植治疗髋关节股骨假体周围骨折的临床治疗效果。方法 对7例髋关节置换术后股骨假体周围骨折患者应用深低温冷冻和环氧乙烷处理同种异体皮质骨板移植治疗股骨骨折。根据Harris评分,外周血T淋巴细胞亚群、抗体和免疫复合物检测、X线摄片以及核素骨显像评价其治疗效果。结果 患者未发生免疫排斥反应和感染,术后3、6、12、24个月Harris评分分别比术前平均增加21、32、40、40分。术后3个月骨折愈合,一部分移植骨板与宿主骨骨性连接,同位素骨显像骨板移植区放射性分布比对侧浓集。术后12个月,85％移植骨板与宿主骨融为一体,宿主股骨皮质厚度增加3～5mm,平均4．3mm,骨板放射性浓集进一步加深,15％移植骨板出现吸收现象。术后24个月,80％移植骨板重新塑形后恢复宿主股骨皮质骨密度,10％骨板表面吸收停止,股骨假体无松动。结论 深低温冷冻和环氧乙烷处理同种异体皮质骨板移植无菌、抗原性弱、生物相容性好,移植骨板能够维持骨折和假体稳定性,增加股骨局部骨量储备,避免再次手术取出金属内置物,是用来治疗股骨假体周围骨折较理想的方法之一。     

Mechanical strength of cortical allografts with gamma radiation versus ethylene oxide sterilization

We investigated the effects of gamma irradiation versus ethylene oxide (ETO) sterilization on the mechanical strength of cortical bone grafts. Tibias were collected from cadavers of mature goats. Sixty test specimens were randomized into four groups: fresh (no processing), frozen (freezing at -70 degrees C), gamma-irradiated, and ETO-sterilized specimens. Torsion, three-point bending, and compression testing were separately performed with a material testing machine. Parameters studied included maximum stress, strain, deflection, extension, load, shear modulus, and E-modulus. Compared with findings for the fresh specimens, findings were as follows for gamma-irradiated specimens: maximal shear modulus, reduced by 48%; shear stress, by 55%; deflection, by 71%; bending stress, by 51%; bending strain, by 74%; extension, by 60%; and compression strain, by 50%. However, there were no reductions in those parameters for the frozen specimens or the ETO-sterilized specimens. These findings confirm that shear, bending, and compression strength of cortical allografts are weakened by gamma irradiation at room temperature. To maintain optimum mechanical properties, ETO sterilization of allografts is better than gamma sterilization, especially for cortical bone, because it is usually used in load-bearing settings.     

Gamma irradiation and ethylene oxide in the sterilization of native reindeer bone morphogenetic protein extract.

BACKGROUND AND AIMS: For human use, it is necessary to sterilize bone morphogenetic proteins (BMPs), in order to reduce the risk of infections and associated complications. We compared the effects of ethylene oxide and gamma irradiation in the sterilization of native reindeer BMP extract with regard to bone induction in the Balb/C mouse thigh muscle pouch model. MATERIALS AND METHODS: BMP extract, sterilized with ethylene oxide gas (Steri-Vac 4XL, temperature 29 degrees C, exposure time 4 h, ethylene oxide concentration 860 mg/l), or gamma irradiation at doses of 3.15 MRad was administered in implants containing 5 or 10 mg of BMP extract with collagen carrier. Non-sterilized collagen implants served as controls. New bone formation was evaluated based on the incorporation of Ca45 and radiographically three weeks after implantation. RESULTS: The collagen was not able to induce new bone visible in radiographs. The mean Ca45 incorporation in the gamma sterilized group containing 5 mg of BMP extract was 30% (p = 0.04) and that containing 10 mg of BMP extract was 60% (p = 0.02) higher than seen in the corresponding ethylene oxide sterilized groups. The mean new bone areas were 45% higher in the gamma sterilized groups than in the corresponding ethylene oxide sterilized groups, but the differences were not significant. The mean optical density of new bone in the gamma sterilized group containing 5 mg of BMP extract was 75% (p = 0.00) and in that containing 10 mg of BMP extract was 70% (p = 0.00) higher than seen in the corresponding ethylene oxide sterilized groups. CONCLUSION: Native reindeer BMP extract is more sensitive to the effects of ethylene oxide gas sterilization than gamma irradiation. These results suggest that gamma irradiation is recommendable for the sterilization of BMP extracts.     

External fixator pin design.

The integrity of the bone-pin interface is the critical link in the stability of external fixation systems. External fixation pins placed in cancellous metaphyseal bone frequently loosen over time, resulting in fixation failure and an increased risk of infection. To design an external fixation pin with optimal bone-metal interface strength in cancellous bone, a systematic study of various thread design features was performed. Combinations of pitch, tooth profile, and minor diameter in 5 mm self-tapping half pins were evaluated in coaxial pullout testing using a fresh bovine cancellous bone. A significant increase in pullout strength was found with a decrease in minor diameter. No statistical differences were found in pullout strength attributable to thread profile and pitch. There were no significant interactions between minor diameter and tooth profile or minor diameter and pitch. The data obtained suggest significantly greater holding power in cancellous bone can be achieved by using an external fixation pin with a smaller minor diameter or a larger interference. Additional pullout testing of five commercially available external fixator pins was performed. Of these, the two pins with the largest interference demonstrated greater pullout strength. Therefore, within a range of acceptable major diameters and adequate minor diameters for the torsional strength requirements, an optimal interference for cancellous pin application may exist and it may well be larger than that present in currently available external fixation pins.     

A finite element study of a fractured tibia treated with a unilateral external fixator: The effects of the number of pins and cortical thickness

IntroductionIn the early stage of fracture fixation, the aim of a unilateral external fixator (UEF) to stimulate healing and maintain stability may be suppressed by using inadequate number of pins. Cortical thinning due to age or osteoporosis endangers a successful fracture fixation.Materials and methodsThis study evaluates the initial strength and stability of the fracture fixation and tissue differentiation under the influences of variable cortical thickness (5 mm to 1 mm) and variable number of pins (1 to 4 in each bone fragment). A finite element program was utilised to develop 20 three-dimensional models of simplified diaphyseal tibia with fracture callus fixed with UEF. A mechano-regulation code based on the deviatoric strain theory was written and applied to simulate tissue differentiation. The values of von Mises stress, interfragmentary strain (IFS), and fibrocartilage index (FCI) were evaluated.ResultsCortical thinning from 5 mm to 1 mm increased IFS and FCI by an average of 30.3% and 18.7%, respectively, and resulted in higher stresses in the UEF and bone. Using 1 pin in each bone fragment produced excessive IFS in the models with 1 mm, 2 mm and 3 mm cortical thickness. Inserting the second pin into the bone fragment could considerably reduce the IFS and fibrocartilaginous tissue formation in the fracture site and improve load transmission to the fixator. Whereas inserting the fourth pin could minimally affect the mechano-biological environment of healing.ConclusionsThis study suggests that initial instability due to cortical thinning can be efficiently alleviated by adding the number of pins up to 3 in a UEF; additionally, it may improve the knowledge about applying UEFs adequately stable, whilst promoting inclination toward endochondral ossification, simultaneously.     

Mechanical evaluation of cross pins used for femoral fixation of hamstring grafts in ACL reconstructions

The goal of this study was to test the mechanical strength of 4 different cross pins currently available for femoral fixation by loading each cross pin to failure as received and determine the effect of 1 million cycles of fatigue loading. Additionally, the strength of resorbable pins was tested after prolonged exposure to biologic conditions. Six implants each of the Arthrotek LactoSorb (Biomet, Warsaw, Indiana), Mitek RigidFix (DePuy Mitek Inc, Raynham, Massachusetts), Arthrotek Bone Mulch Screw (Biomet), cortical allograft, and control were tested for 3-point failure without prior loading and after cyclic loading between 50 to 200 N at 10 Hz for 1 million cycles. The bioabsorbable pins were placed in sterile water at 37°C and tested after 2, 4, and 6 months for 3-point failure strength. All implants tested without antecedent loading demonstrated adequate strength for initial fixation for hamstring grafts. During fatigue testing, RigidFix implants (n=6) failed at 18,893±8365 cycles (with a central deformation of 0.48±0.11 mm prior to fracture). All of the other implants tested endured 1 million cycles of loading (50-200 N) without fracture or 1.5 mm central deformation. Neither of the bioabsorbable pins demonstrated a significant change in yield strength after prolonged exposure to water. All implants tested demonstrated adequate strength for initial fixation of hamstring grafts. The metal and bone implants far exceed the strength required to sustain mechanical fixation until biological fixation occurs; both polymeric implants demonstrated that they maintained enough mechanical strength to achieve this goal.     

Locking plates for corrective osteotomy of malunited dorsally tilted distal radial fractures: a biomechanical study

The purpose of the study was to compare the biomechanical properties of five different palmar fixation plate designs in a distal radius osteotomy cadaver model. A 1cm metaphyseal osteotomy gap was made to simulate a corrective osteotomy and the osteotomy plated. Axial load was applied to the distal end of each construct by a material testing machine under control of a motion analysis video system. The specimens were arranged into five implant groups of eight specimens each. No test group developed deformity and movement of the fracture gap greater than 2mm with a load of 100N. Increasing the load to 250N revealed statistically significant differences in stiffness and failure load between the different plates. Axial failure strength and stiffness were greater for the radial correction plates than for the other implants. The former may provide enough stability for corrective osteotomy of dorsally angulated distal radial malunions, even when the osteotomy gap is only filled with cancellous bone graft instead of cortical bone graft.     

Durability and strength of Steinmann pin augmentation in cemented tibial defects

It has been argued that Steinmann pin augmentation does not improve the biomechanics of polymethylmethacrylate reconstruction for massive defects of bone. The current authors investigated whether pin augmentation of polymethylmethacrylate in the reconstruction of noncontained defects of bone improved the biomechanical properties of the reconstruction as compared with polymethylmethacrylate alone when minimal or large bone porosity is present. Large noncontained defects were created in 10 pairs of human tibias. In Group 1, five left tibias had reconstruction with polymethylmethacrylate augmented with three, 5-mm diameter by 10-mm deep holes into lateral condyle cancellous bone. Right tibias had identical reconstruction with three, 3/16-inch threaded pins placed into the medullary canal. In Group 2, three, 10-mm diameter by 10-mm deep holes were created in both pairs. The left tibia had polymethylmethacrylate reconstruction and the right tibia had polymethylmethacrylate and pin augmentation. Specimens were subjected to 2000 compressive cycles then loaded to failure. In Group 1, cycles and load to failure were significantly lower in reconstructions without pins compared with reconstructions with pins. No significant difference was observed between reconstruction techniques in Group 2. In reconstructions without pins, large diameter holes had significantly better cyclical durability. Pins improved survival compared with no pins.     

The influence of bone allograft processing on osteoblast attachment and function.

In order to assess the influence of eight different sterilisation and disinfection methods for bone allografts on adhesion, proliferation, and differentiation of human bone marrow stromal cells (BMSC), cells were grown in culture and then plated onto pieces of human bone allografts. Following processing methods were tested: autoclavation (AUT), low-temperature-plasma sterilisation of demineralised allografts (D-LTP), ethylene oxide sterilisation (EtO), fresh frozen bone (FFB), 80 degrees C-thermodisinfection (80 degrees C), gamma-irradiation (Gamma), chemical solvent disinfection (CSD), and Barrycidal-disinfection (BAR). The seeding efficiency was determined after one hour to detect the number of attached cells before mitosis started. The cell viability was determined after 3, 7, and 21 days. Tests to confirm the osteoblastic differentiation included histochemical alkaline phosphatase staining and RT-PCR for osteocalcin. Human BMSC showed greatest attachment affinities for D-LTP-, 80 degrees C-, and CSD-allografts, whereas less cells were found attached to AUT-, EtO-, FFB-, Gamma-, and BAR-probes. Cell viability assays at day 3 revealed highest proliferation rates within the FFB- and 80 degrees C-groups, whereas after 21 days most viable cells were found in D-LTP-, 80 degrees C-, CSD-, and Gamma-groups. BAR-treatment showed a considerably toxic effect and therefore was excluded from all further experiments. Highest AP-activity and gene expression of osteocalcin were detected in the D-LTP-group in comparison with all other groups. In summary, our results demonstrate that cell adhesion, final population, and function of BMSC are influenced by different disinfection and sterilisation methods. Therefore, processing-related alterations of BMSC-function may be important for the success of bone grafting. The experimental setup used in the present work may be useful for further optimisation of bone allograft processing.     

Effect of sterilization on bone morphogenetic protein

Demineralized bone matrix and bone morphogenetic protein have been used clinically to accelerate bone regeneration. However, the best method of sterilization has been the subject of controversy. Some investigators have used ethylene oxide, but others have reported that doses adequate for sterilization destroyed the osteoinductivity of demineralized bone matrix and that gamma irradiation was less harmful in this respect. We used partially purified bone morphogenetic protein and type-I collagen to investigate the effects of sterilization by ethylene oxide and gamma irradiation on the activity of bone morphogenetic protein. Osteoinductivity was reduced considerably after sterilization by gamma irradiation at 2.5 Mrad and by ethylene oxide at 37°C for 4 hours and at 55°C for 1 hour; however, the reduction induced by ethylene oxide at 29°C for 5 hours was about half of the control values. This study showed that ethylene oxide at 29°C for 5 hours can be used clinically for sterilization of bone morphogenetic protein. We also investigated the effect of gamma irradiation on bone morphogenetic protein and the collagen carrier separately and found that collagen was far more labile than bone morphogenetic protein.     

Fixation strength and pin tract infection of hydroxyapatite-coated tapered pins.

In a multicenter, prospective, randomized study, the biomechanical and clinical properties of the bone-pin interface were compared with standard tapered pins and hydroxyapatite-coated tapered pins implanted in patients who underwent femoral and tibial external fixation treatments. The results showed that the hydroxyapatite-coated tapered pins are clinically effective in improving the strength of fixation of the bonepin interface. This improvement corresponded to a lower rate of pin tract infection. In the hydroxyapatite-coated pin group, there were no differences in strength of fixation between the pins removed from the infected and uninfected pin tracts. In this pin group, the mean pin extraction torque was 531 +/- 225 Ncm in the infected pin tracts and 508 +/- 233 Ncm in the uninfected pin tracts. In the standard pin group, the mean pin extraction torque was 73 +/- 142 Ncm in the infected pin tracts and 211 +/- 216 Ncm in the uninfected pin tracts. The advantages provided by the hydroxyapatite-coated pins were higher in cancellous bone than in cortical bone.     

羟基磷灰石涂层钢板螺钉改善骨折稳定性的实验研究

目的　比较国产羟基磷灰石 (hydroxyapatite ,HA)涂层钢板螺钉与非涂层钢板螺钉在体负重情况下对骨折的内固定效果。方法　四孔钢板螺钉 2 4套 ,附加螺钉 60枚 ,对其中 12套钢板、30枚螺钉行HA等离子喷涂 ,其余的钢板、螺钉不喷。 12只成年杂种犬 ,每只犬的两侧肱骨线型骨折后分别以HA涂层钢板、螺钉或非涂层钢板、螺钉内固定 ,每只犬的右胫骨间隔 2cm交递置入HA涂层钉和非涂层钉共 5枚。按术后即刻、3、6周将犬分成 3组。处死后行组织学观察和生物力学测试。结果　组织学观察 :术后 3、6周组HA涂层均无明显降解 ,其与不锈钢基底结合良好 ,与骨组织结合紧密 ,3、6周组HA涂层钢板下都有不同程度的皮质骨上新生骨形成 ,该处未见明显的骨质疏松。相反非涂层钢板、螺钉与骨接触不紧密 ,其间有薄层纤维组织生长 ,钢板下可见不同程度的骨质疏松。力学测试 :3、6周组犬中HA涂层组的三点折弯强度及螺钉拔出强度均比非涂层组大。结论　国产HA涂层的钢板螺钉可增加骨折内固定的稳定性。     

Restoration of bone flow following fracture and reaming in rat femora

In rats, bilateral closed femoral fracture was produced after intramedullary reaming to 1.6 mm on the left side and 2.0 mm on the right side. The fractures were fixed with 1.6 and 2.0 mm steel pins. Radioactive microspheres were used to determine bone blood flow at 30 min, 1 day, 3 days and 9 days after fracture. 8 rats were used to estimate normal bone blood flow, and an additional 8 rats to examine the vascular effects of fracture only.

Following fracture, total bone blood flow was reduced to about 50 percent and cortical flow to about 40 percent of that in intact bones. Fracture and reaming to 1.6 mm reduced total bone flow to 40 percent and reaming to 2.0 mm reduced the total bone flow to approximately one third of normal flow. Cortical flow decreased to about one third and one quarter in the 2 groups. On Day 1, total flow was practically normalized in both groups. Cortical flow in the 1.6 mm group was about equal to that of intact bones, while it was about one third of normal flow in the 2.0-mm group, and significantly less than the 1.6-mm group. On Day 3, total bone flow was more than double that of intact bones and cortical flow 3 times greater in both groups. Flow continued to increase to Day 9 when a threefold increase in total bone blood flow and approximately a fivefold increase in cortical flow were found. On Day 9, a separate callus area was defined and flow measurement revealed a rich vascularized callus in both groups, but no differences between the groups were found.

Following fracture, neither moderate nor aggressive intramedullary reaming seem to create any further impairment in bone flow. Following fracture and reaming, blood flow is rapidly restored, however, extensive reaming results in a delayed restoration of cortical bone blood flow. After 9 days, rich vascularized callus areas were found irrespective of the initial degree of reaming.     

海绵状、泥灰状脱钙骨基质修复骨缺损

目的探讨海绵状脱钙骨基质(DBM)和泥灰状DBM修复骨缺损的能力。方法将兔四肢长骨骨干脱脂、脱钙后制成长度为500～1000 μm的纤维状及直径为200～400μm的颗粒状DBM,并与2%明胶混合分别制成海绵状DBM和泥灰状DBM。在9只兔双侧桡骨中段做一长10mm的骨膜骨缺损,分别植入海绵状DBM和泥灰状DBM及空白对照,每组各6个缺损,术后观察6周,于4、6周时拍摄X线片,并对实验动物的大体标本、骨密度、生物力学、新生骨矿化率及病理组织学改变进行观察。结果术后4、6周X线片显示两实验组骨缺损均修复,骨髓腔完整;空白对照组无一例修复骨缺损。骨密度测量显示海绵状DBM组新生骨骨密度与正常桡骨间差异无显著性(P >0.05),但泥灰状DBM组的新生骨骨密度与正常桡骨间差异有显著性(P< 0.05)。术后6周生物力学测定显示海绵状DBM组新生骨极限压缩强度值与正常桡骨差异无显著性(P >0.05),泥灰状DBM组低于正常桡骨且差异有显著性(P< 0.05)。两实验组新生骨矿化率差异无显著性(P >0.05)。组织学观察显示两实验组中DBM绝大部分被吸收,形成板状骨骨小梁及完整的骨髓腔,塑形完整, 新生骨内可见骨单位及局部尚未完全骨化的新生骨。结论海绵状DBM和泥灰状DBM均具有诱导成骨活性和骨传导能力,使用方便,新生骨塑形完整,生物力学强度高,矿化     

Graft perforations favor osteoinduction. Studies of rabbit cortical grafts sterilized with ethylene oxide.

The healing of freeze-dried, ethylene oxide sterilized, segmental, allogenic cortical bone grafts was investigated in 15 rabbits using a 2-cm ulnar diaphyseal defect. Five different groups of bone grafts were evaluated: 1) unperforated undemineralized, 2) perforated undemineralized, 3) unperforated demineralized, 4) perforated demineralized, and 5) perforated demineralized grafts enclosed by silicone rubber (Silastic) sheets. There were 3 animals in each group. At 18 days, the study was terminated, and the implants were examined using radiographs and qualitative histologic preparations. We observed that healing of perforated demineralized bone was superior to unperforated demineralized bone, that undemineralized bone was partially sequestered in reactive lacunae, and that perforations in demineralized bone became centers of osteoinduction. Demineralized bone sterilized with ethylene oxide by this method vigorously formed new bone.     

Free radical scavenging alleviates the biomechanical impairment of gamma radiation sterilized bone tissue.

Terminal sterilization of bone allografts by gamma radiation is often essential prior to their clinical use to minimize the risk of infection and disease transmission. While gamma radiation has efficacy superior to other sterilization methods it also impairs the material properties of bone allografts, which may result in premature clinical failure of the allograft. The mechanisms by which gamma radiation sterilization damages bone tissue are not well known although there is evidence that the damage is induced via free radical attack on the collagen. In the light of the existing literature, it was hypothesized that gamma radiation induced biochemical damage to bone's collagen that can be reduced by scavenging for the free radicals generated during the ionizing radiation. It was also hypothesized that this lessening of the extent of biochemical degradation of collagen will be accompanied by alleviation in the extent of biomechanical impairment secondary to gamma radiation sterilization. Standardized tensile test specimens machined from human femoral cortical bone and specimens were assigned to four treatment groups: control, scavenger treated-control, irradiated and scavenger treated-irradiated. Thiourea was selected as the free radical scavenger and it was applied in aqueous form at the concentration of 1.5 M. Monotonic and cyclic mechanical tests were conducted to evaluate the mechanical performance of the treatment groups and the biochemical integrity of collagen molecules were assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The native mechanical properties of bone tissue did not change by thiourea treatment only. The effect of thiourea treatment on mechanical properties of irradiated specimens were such that the post-yield energy, the fracture energy and the fatigue life of thiourea treated-irradiated treatment group were 1.9-fold, 3.3-fold and 4.7-fold greater than those of the irradiated treatment group, respectively. However, the mechanical function of thiourea treated and irradiated specimens was not to the level of unirradiated controls. The damage occurred through the cleavage of the collagen backbone as revealed by SDS PAGE analysis. Irradiated specimens did not exhibit a noteworthy amount of intact alpha-chains whereas those irradiated in the presence of thiourea demonstrated intact alpha-chains. Results demonstrated that free radical damage is an important pathway of damage, caused by cleaving the collagen backbone. Blocking the activity of free radicals using the scavenger thiourea reduces the extent of damage to collagen, helping to maintain the mechanical strength of sterilized tissue. Therefore, free radical scavenger thiourea has the potential to improve the functional life-time of the allograft component following transplantation.     

Cytotoxic effects exerted by polyarylsulfone dialyser membranes depend on different sterilization processes

Polyarylsulfone group is one of the most important polymeric materials used in the biomedical field, due to its excellent properties, such as good thermal, chemical, and mechanical stability. There are three important polyarylsulfone polymers, all of which have excellent electrical properties: polysulfone (PSu), polyarylsulfone (PAS) and polyarylethersulfone (PAES). All these polymers have excellent creep, radiation and high temperature resistance. In this study, we aimed to determine the effect of three sterilization processes (steam, ethylene oxide and gamma rays) on cytotoxicity of polyarylsulfone dialysis membranes. Ten long-term dialysis patients and ten age-matched healthy controls were enrolled in our study. We analysed (1) serum effect on cultured endothelial cell viability using MTT assay and (2) lipid peroxidation assessed by serum malondialdehyde (MDA) formation at the beginning (T0), the middle (T2) and the end (T4) of haemodialysis (HD) session. Our results clearly showed that steam-sterilized membranes improve endothelial cell viability when compared to ethylene oxide or gamma rays-sterilized ones. Moreover, there is a increased generation of MDA in patients sera during HD session. The serum MDA concentration was about 3, 6 and 10 times higher, respectively, for steam, ethylene oxide and gamma rays sterilization procedures when compared to the MDA amount in healthy subject sera. We concluded that using steam instead of ethylene oxide or gamma rays for sterilization may improve the biocompatibility of polyarylsulfone membranes.     

Influence of pins configuration to balance of general transversal stability in long bone fractures external fixation

Biomechanical features of long bones indicate that external fixation of long bone fractures have to be balanced according to general transversal stability as more as possible. The aim of this work was to investigate the influence of orientation pins to the general transversal stability of external fixation of fractures of long bones. In this study we have used the model of fractured long bone made of wood which was treated by Mitkovic external fixator with 4 pins, in 3 different situations: (1) all pins are in one axial plane, (2) each 2 pins are in 2 axial planes with angle distances of 60 degrees, (3) each 2 pins are in 2 axial planes wich are normal to each other. Means of relations of measured movements of long bone model fragments during the use of perpendicular force from 2 directions, normal to each other, after grouping of results in 3 grous: 0.17, 0.46 and 0.72. Statistical analyses showed that the differences between each of 3 grous were significant (p < 0.05). It can be concluded that it is better if pins are oriented in different axial planes, with pretension that both planes are normal to each other, during external fixation of long bone fractures.