Biomechanical performance of different cable and wire cerclage configurations

Purpose

Cerclage technology is regaining interest due to the increasing number of periprosthetic fractures. Different wiring techniques have been formerly proposed and have hibernated over years. Hereby, they are compared to current cerclage technology.

Methods

Seven groups (n = 6) of different cable cerclage (Ø1.7 mm, crimp closure) configurations (one single cerclage looped once around the shells, one single cerclage looped twice, two cerclages each looped once) and solid wire cerclages (Ø1.5 mm, twist closure) (same configurations as cable cerclages, and two braided wires, twisted around each other looped once) fixed two cortical half shells of human femoral shaft mounted on a testing jig. Sinusoidal cyclic loading with constantly increasing force (0.1 N/cycle) was applied starting at 50 N peak load. Cerclage pretension (P), load leading to onset of plastic deformation (D) and load at total failure (T) were identified. Statistical differences between the groups were detected by univariate ANOVA.

Results

Double looped cables (P442N ± 129; D1334N ± 319; T2734N ± 330) performed significantly better (p < 0.05) than single looped cables (P292N ± 56; D646N ± 108; T1622N ± 171) and were comparable to two single cables (P392N ± 154; D1191N ± 334; T2675N ± 361). Double looped wires (P335N ± 49; D752N ± 119; T1359N ± 80) were significantly better (p < 0.05) than single looped wires (P181N ± 16; D343N ± 33; T606N ± 109) and performed similarly to single looped cables. Braided wires (P119N ± 26; D225N ± 55; T919N ± 197) exhibited early loss of pretension and plastic deformation.

Conclusion

Double looped cerclages provided a better fixation stability compared to a single looped cerclage. Double looped wires were comparable to a single looped cable. The use of braided wires could not be recommended mechanically.     

Fatigue performance of angle-stable tibial nail interlocking screws

Purpose

Tibial nail interlocking screw failure often occurs during delayed fracture consolidation or at early weight bearing of nailed unstable fractures, in general when high implant stress could not be reduced by other means. Is there a biomechanical improvement in long-term performance of angle stable locking screws compared to conventional locking screws for distal locking of intramedullary tibial nails?

Methods

Surrogate bones of human tibiae were cut in the distal third and distal locking of the 10 mm intramedullary tibial nail was performed with either two angle stable locking screws or two conventional locking screws in the mediolateral plane. Six specimens per group were mechanically tested under quasi-static and cyclic axial loading with constantly increasing force.

Results

Angle stable locking screw constructs exhibited significantly higher stiffness values (7,809 N/mm ± 647, mean ± SD) than conventional locking screw constructs (6,614 N/mm ± 859, p = 0.025). Angle stable locking screw constructs provided a longer fatigue life, expressed in a significantly higher number of cycles to failure (187,200 ± 18,100) compared to conventional locking screw constructs (128,700 ± 7,000, p = 0.004).

Conclusion

Fatigue performance of locking screws can be ameliorated by the use of angle stable locking screws, being especially important if the nail acts as load carrier and an improved stability during fracture healing is needed.     

Chronic Exposure to Deoxynivalenol Has No Influence on the Oral Bioavailability of Fumonisin B1 in Broiler Chickens

Both deoxynivalenol (DON) and fumonisin B₁ (FB₁) are common contaminants of feed. Fumonisins (FBs) in general have a very limited oral bioavailability in healthy animals. Previous studies have demonstrated that chronic exposure to DON impairs the intestinal barrier function and integrity, by affecting the intestinal surface area and function of the tight junctions. This might influence the oral bioavailability of FB₁, and possibly lead to altered toxicity of this mycotoxin. A toxicokinetic study was performed with two groups of 6 broiler chickens, which were all administered an oral bolus of 2.5 mg FBs/kg BW after three-week exposure to either uncontaminated feed (group 1) or feed contaminated with 3.12 mg DON/kg feed (group 2). No significant differences in toxicokinetic parameters of FB₁ could be demonstrated between the groups. Also, no increased or decreased body exposure to FB₁ was observed, since the relative oral bioavailability of FB₁ after chronic DON exposure was 92.2%.     

Phorbol 12-myristate 13-acetate, ionomycin or ouabain, and raised extracellular magnesium induce proliferation of chicken heart mesenchymal cells.

Cultured chicken heart mesenchymal cells are proliferatively quiescent at low densities in medium containing plasma at 10%. Mitogenic hormones like epidermal growth factor and insulin-like growth factors cause these cells to proliferate very actively, as does infection with avian sarcoma viruses, erythroblastosis virus, or myelocytomatosis virus. We have found that the combination of phorbol 12-myristate 13-acetate (PMA), ionomycin or ouabain, and raised extracellular magnesium, likewise, causes these cells to proliferate very actively. Although these agents have no significant effect when acting singly, the combination of PMA at 100 ng/ml and 0.5 microM ionomycin induces a 6-fold increase in cell number at 4 days, and the combination of PMA, ionomycin, and 5.6 mM magnesium induces 12-fold multiplication. Likewise, PMA plus 1 microM ouabain induces 3-fold multiplication, whereas the combination of PMA, ouabain, and magnesium induces 6-fold multiplication. The tumor promoter PMA, like diacylglycerol released by breakdown of plasma membrane phosphatidylinositol diphosphate, is known to activate the serine- and threonine-specific intracellular enzyme kinase C. The divalent cation ionophore ionomycin is known to carry calcium into cells down an electrochemical gradient, and the Na+,K+-ATPase inhibitor ouabain appears to elevate intracellular calcium by means of a sodium-mediated exchange mechanism. Magnesium, like calcium, is known to enter cells passively down an electrochemical gradient and to be involved in the regulation of many key intracellular reactions. Our findings with PMA, ionotropes, and magnesium support a hypothesis that diacylglycerol-mediated activation of kinase C plus cellular divalent cation influx and/or mobilization, caused by the action of mitogenic hormones or the protein products of onc genes, are key events in the initiation of cell replication.     

CpG-A and CpG-B oligonucleotides differentially enhance human peptide-specific primary and memory CD8+ T-cell responses in vitro

Two distinct types of CpG oligodeoxynucleotide (ODN) have been identified that differ in their capacity to stimulate antigen-presenting cells: CpG-A induces high amounts of interferon-alpha (IFN-alpha) and IFN-beta in plasmacytoid dendritic cells (PDCs), whereas CpG-B induces PDC maturation and is a potent activator of B cells but stimulates only small amounts of IFN-alpha and IFN-beta. Here we examined the ability of these CpG ODNs to enhance peptide-specific CD8+ T-cell responses in human peripheral blood mononuclear cells (PBMCs). The frequency of influenza matrix-specific "memory" CD8+ T cells was increased by both types of CpG ODN, whereas the frequency of Melan-A specific "naive" CD8+ T cells increased on stimulation with CpG-B but not with CpG-A. The presence of PDCs in PBMCs was required for this CpG ODN-mediated effect. The expanded cells were cytotoxic and produced IFN- on peptide restimulation. Soluble factors induced by CpG-A but not CpG-B increased the granzyme-B content and cytotoxicity of established CD8+ T-cell clones, each of which was IFN-alpha/-beta dependent. In conclusion, CpG-B seems to be superior for priming CD8+ T-cell responses, and CpG-A selectively enhances memory CD8+ T-cell responses and induces cytotoxicity. These results demonstrate distinct functional properties of CpG-A and CpG-B with regard to CD8 T cells.     

Transapical mitral valved stent implantation: Enhanced survival and decreased paravalvular leakages

Background/Objectives

This study presents the recent results of transapical implantation of a new design of a mitral valved stent with up to three months follow-up.

Methods

A self-expanding re-designed mitral valved stent was implanted via transapical approach into the beating heart of eight pigs. Echocardiographic- and hemodynamic parameters were assessed before (n = 8), at 1 h (n = 8), at one month (n = 6), at two months (n = 2), and at three months (n = 1) after implantation and a cardiac CT was conducted.

Results

The stent was successfully deployed in all animals. Two animals died within the first month due to incorrect fixation force. Echocardiographic evaluation showed low gradients (3.9 ± 1.4 mm Hg and 1.9 ± 0.8 mm Hg across the valved stent and aortic valve) and a normal mitral annular plane systolic excursion (1.1 ± 0.2 cm) after one month. No paravalvular leakages (PVL) were detected after 1 h. The pulmonary artery pressure did not increase after valved stent implantation (p ≥ 0.106). The pulmonary capillary wedge pressure (PCWP) slightly increased to 16 ± 3 mm Hg after one month (p = 0.033). The left ventricular end-diastolic pressure was mildly elevated (15.8 ± 8.6 mm Hg) after one month.

Conclusions

Secure deployment and correct position of the valved stents were reproducibly achieved in the off-pump implantation procedure. No paravalvular leakages after 1 h as well as low gradients, few stent fractures and a normal longitudinal function after one month were achieved with this newly developed and well-aligned prototype. However, a number of challenges have been identified during this study and potential for improvement has been identified.