Externalised locking compression plate as an alternative to the unilateral external fixator: a biomechanical comparative study of axial and torsional stiffness.

OBJECTIVES: External fixators are the traditional fixation method of choice for contaminated open fractures. However, patient acceptance is low due to the high profile and therefore physical burden of the constructs. An externalised locking compression plate is a low profile alternative. However, the biomechanical differences have not been assessed. The objective of this study was to evaluate the axial and torsional stiffness of the externalised titanium locking compression plate (ET-LCP), the externalised stainless steel locking compression plate (ESS-LCP) and the unilateral external fixator (UEF). METHODS: A fracture gap model was created to simulate comminuted mid-shaft tibia fractures using synthetic composite bones. Fifteen constructs were stabilised with ET-LCP, ESS-LCP or UEF (five constructs each). The constructs were loaded under both axial and torsional directions to determine construct stiffness. RESULTS: The mean axial stiffness was very similar for UEF (528 N/mm) and ESS-LCP (525 N/mm), while it was slightly lower for ET-LCP (469 N/mm). One-way analysis of variance (ANOVA) testing in all three groups demonstrated no significant difference (F(2,12) = 2.057, p = 0.171).There was a significant difference in mean torsional stiffness between the UEF (0.512 Nm/degree), the ESS-LCP (0.686 Nm/degree) and the ET-LCP (0.639 Nm/degree), as determined by one-way ANOVA (F(2,12) = 6.204, p = 0.014). A Tukey post hoc test revealed that the torsional stiffness of the ESS-LCP was statistically higher than that of the UEF by 0.174 Nm/degree (p = 0.013). No catastrophic failures were observed. CONCLUSION: Using the LCP as an external fixator may provide a viable and attractive alternative to the traditional UEF as its lower profile makes it more acceptable to patients, while not compromising on axial and torsional stiffness.Cite this article: B. F. H. Ang, J. Y. Chen, A. K. S. Yew, S. K. Chua, S. M. Chou, S. L. Chia, J. S. B. Koh, T. S. Howe. Externalised locking compression plate as an alternative to the unilateral external fixator: a biomechanical comparative study of axial and torsional stiffness. Bone Joint Res 2017;6:216-223. DOI: 10.1302/2046-3758.64.2000470.

Cannulated versus non-cannulated cancellous screw fixation for femoral neck fractures: a synthetic bone biomechanical study.

PURPOSE: To compare the compressive strength of cannulated versus non-cannulated cancellous screws for undisplaced femoral neck fractures in synthetic bones. METHODS: 18 synthetic proximal femurs simulating an AO B1 valgus impacted femoral neck fracture in osteoporotic bone were used. The fracture angles were between 55º and 63º (Pauwels grade 2). Fixation was made using 6.5-mm non-cannulated screws (n=6), 6.5-mm cannulated screws (n=6), or 7.3-mm cannulated screws (n=6). A custom-built jig was designed to guide the insertion of the screws in an identical triangular configuration. Screws were tightened by a single operator using a torque-measuring screwdriver. The femoral head was subjected to progressive axial loading at 5 mm/min. The load to failure and displacement were recorded. RESULTS: The 3 groups did not differ significantly except that the load to failure was higher in the construct with 6.5-mm non-cannulated screws than that with 6.5-mm cannulated screws (1222 N vs 1008 N, p=0.003). CONCLUSION: The compressive strength of a synthetic bone hip fracture model fixed with non-cannulated screws was higher than that of cannulated screws of the same diameter.

The development of silk fibroin scaffolds using an indirect rapid prototyping approach: morphological analysis and cell growth monitoring by spectral-domain optical coherence tomography.

To date, naturally derived biomaterials are rarely used in advanced tissue engineering (TE) methods despite their superior biocompatibility. This is because these native materials, which consist mainly of proteins and polysaccharides, do not possess the ability to withstand harsh processing conditions. Unlike synthetic polymers, natural materials degrade and decompose rapidly in the presence of chemical solvents and high temperature, respectively. Thus, the fabrication of tissue scaffolds using natural biomaterials is often carried out using conventional techniques, where the efficiency in mass transport of nutrients and removal of waste products within the construct is compromised. The present study identified silk fibroin (SF) protein as a suitable material for the application of rapid prototyping (RP) or additive manufacturing (AM) technology. Using the indirect RP method, via the use of a mould, SF tissue scaffolds with both macro- and micro-morphological features can be produced and qualitatively examined by spectral-domain optical coherence tomography (SD-OCT). The advanced imaging technique showed the ability to differentiate the cells and SF material by producing high contrasting images, therefore suggesting the method as a feasible alternative to the histological analysis of cell growth within tissue scaffolds.

Effects of frozen storage temperature on the elasticity of tendons from a small murine model.

The basic mechanism of reinforcement in tendons addresses the transfer of stress, generated by the deforming proteoglycan (PG)-rich matrix, to the collagen fibrils. Regulating this mechanism involves the interactions of PGs on the fibril with those in the surrounding matrix and between PGs on adjacent fibrils. This understanding is key to establishing new insights on the biomechanics of tendon in various research domains. However, the experimental designs in many studies often involved long sample preparation time. To minimise biological degradation the tendons are usually stored by freezing. Here, we have investigated the effects of commonly used frozen storage temperatures on the mechanical properties of tendons from the tail of a murine model (C57BL6 mouse). Fresh (unfrozen) and thawed samples, frozen at temperatures of -20°C and -80°C, respectively, were stretched to rupture. Freezing at -20°C revealed no effect on the maximum stress (σ), stiffness (E), the corresponding strain (ε) at σ and strain energy densities up to ε (u) and from ε until complete rupture (up). On the other hand, freezing at -80°C led to higher σ, E and u; ε and up were unaffected. The results implicate changes in the long-range order of radially packed collagen molecules in fibrils, resulting in fibril rupture at higher stresses, and changes to the composition of extrafibrillar matrix, resulting in an increase in the interaction energy between fibrils via collagen-bound PGs.

Enzymatic degradation of nitriles by Klebsiella oxytoca.

Klebsiella oxytoca, isolated from cyanide-containing wastewater, was able to utilize many nitriles as sole source of nitrogen. The major objective of this study was to explore the ability of K. oxytoca to utilize some nitriles and then further evaluate the pathways of transformation of cyanide compounds by K. oxytoca. Results from this study indicate that succinonitrile and valeronitrile were the most optimal sources of nitrogen for the growth of K. oxytoca. The biodegradation of acetonitrile proceeded with the formation of acetamide followed by acetic acid. The production of ammonia was also detected in this biodegradation experiment. Similar results were observed in the propionitrile biodegradation experiments. Collectively, this study suggests that the breakdown of acetonitrile or propionitrile by this bacterium was via a two-step enzymatic hydrolysis with amides as the intermediates and organic acids plus with ammonia as the end products.

The influence of gripping techniques on the tensile properties of tendons.

Gripping is a major challenge faced in the tensile testing of tendons. As soft and aqueous materials, tendons are prone to slip and experience premature failure during mechanical testing. Several gripping methods were attempted and evaluated, including serrated jaw, sandpaper, frozen ends, and air-dried ends. It was found that 1 kN pneumatic grips (Shimadzu Company) lined with cardboard provided an adequate grip without perceptible slip and damage to the tendons. It was found that using the pneumatic grips with cardboard lining the stress concentration at the grip-specimen interface reduced substantially. An analysis of specimens that failed at the grip-specimen interface versus those that failed at mid-substance shows that there was no significant difference in their tensile properties.

Patellar resection during total knee arthroplasty: effect on bone strain and fracture risk.

Patellae in small knees, or after severe patellar erosion, may be vulnerable to fracture after resection during arthroplasty. The patellar remnant may be thin, while the polyethylene component has a standard thickness. Anterior patellar bone strain was measured in cadaver knees loaded via the quadriceps, from 0 to 90 degrees flexion, with the patella intact, and after resections to 16, 13 and 11 mm thick and replacement by an 8-mm-thick polyethylene component. Strain increased significantly with knee flexion with constant 500 N quadriceps tension. Resection caused significant changes from intact values in knee flexion and extension and no significant effect at 30 degrees flexion. In flexion, bending caused the anterior surface to become more convex, with high tensile bone strains. In extension, resection caused negative anterior strains, representing bending in the opposite direction, with large tensile strains on the cut posterior surface. For normal activities, such as rising from a chair (1.8 kN quadriceps tension) the patella appears safe against fracture with a minimal resection to 16 mm thick. An eroded patella resected to 11 mm thickness may be at risk of fracture with that loading.

Strain rate effect on the failure properties of tendons.

The purpose of this study is to evaluate the effect of strain rate on the failure properties of tendons. Seventy-five chicken flexor digitorum profundus (FDP) tendons were tensile tested at 15 strain rates, ranging from 0.05 to 150 per cent/s. Results showed that strain rate had little effect on the shape of the stress-strain curve. No significant change was observed in the toe region, while the slope of the linear region increased with the increase in strain rate. Generally, the ultimate tensile strength (UTS) and elastic modulus increased significantly as strain rate increased (p < 0.01), while no significant change in strain at UTS (p > 0.01) was observed. It was found the change in failure properties of tendons was not significant, with small change in strain rate.

Investigation of fixation screw pull-out strength on human spine.

For the purpose of fixation and stabilizing the spine, the pull-out strength of the screw is one of the most important factors to be considered. The material properties of the bone, coupled with the principal dimensions of the screw such as major diameter, minor diameter, pitch and purchase length, may affect the pull-out strength of the fixation screw. In this study, the effects of various factors on the bone screw pull-out strength were studied using finite element method of analysis. A three-dimensional finite element model simulating the threaded connection of bone and surgical screw was constructed. The behavior of both the bone and the screw during screw pull-out were analyzed and discussed. The effect of the screw parameters on the screw pull-out strength was also investigated. The results showed that failure of the connection was due to bone shearing which occurred along a cylindrical surface determined by the outer perimeter of the screw and penetrated length. The distribution of the shear stress along the threaded length in the bone was nearly uniform. The effect of the major diameter on the screw pull-out strength was more significant than those of the minor diameter and the pitch. The minor diameter hardly affected the pull-out strength.

Towards a splint-free repair for flexor tendon injuries.

Flexor tendon injury has long been recognised as a difficult problem to tackle in hand surgery. Loss of active motion in the digits results in significant morbidity. The increased understanding in tendon healing, role of the tendon sheath, and the development of mobilisation and repair techniques have drastically improved results of flexor tendon injuries over the last 50 years. The treatment of flexor tendon injuries is based on evidence-based medicine, where clinical problems and new concepts were first evaluated in the biomechanical and animal laboratories and clinical practice is dictated by long-term outcome results. However, current surgical repairs are not strong enough to withstand active grip during rehabilitation and patients needed a prolonged period of protected rehabilitation until tendon healing is completed. The need for a more robust repair to allow a splint-free unprotected use of the hand should be the next step forward in the approach to flexor tendon injuries.

Immunohistochemistry of advanced glycation end products in neurofilamentous axonal spheroids induced by beta-beta'-iminodipropionitrile in lower motor neurons of rat.

Chronic parenteral administration of beta-beta'-iminodipropionitrile (IDPN) in adult female rats induces large neurofilament-rich axonal spheroids (AXS) in spinal motor neurons closely resembling those AXS in early phases of amyotrophic lateral sclerosis. Immunohistochemistry of advanced glycosylation end-products (AGEs) in axonal spheroids was performed in the present study. Anti-AGE and anti-neurofilament antibodies strongly co-labeled IDPN-induced axonal spheroids, whereas motor neuron soma showed little AGE immunoreactivity. In an attempt to modify and intensify glycosylation, another group of IDPN rats was made hyperglycemic with streptozotocin after IDPN intoxication. These hyperglycemic rats showed AXS with striking AGE immunoreactivity. An additional group of rats made hyperglycemic before IDPN intoxication showed markedly diminished AXS formation, with a few small AGE-positive AXS in anterior horns. Findings suggest that AGEs are involved in neurofilament crosslinking as well as disassembly of neurofilament induced by IDPN with or without hyperglycemia. Hyperglycemia did not intensify neurofilament aggregation. Additional immunohistochemistry revealed not only aberrant phosphorylation, but also intense local production of Cu/Zn superoxide dismutase and nitrotyrosine in axonal spheroids, probably secondary to superoxide generation as a consequence of AGE production at neurofilament protein, impeding its assembly as hypothesized in motoneuron diseases.

A receptor for advanced glycosylation endproducts (AGEs) is colocalized with neurofilament-bound AGEs and SOD1 in motoneurons of ALS: immunohistochemical study.

Neurofilament (NF)-bound AGEs colocalize immunochemically with SOD1 in the motoneurons of patients with ALS. Among three types of AGE receptors reported in the human brain, AGE-R1 (oligosaccharyltransferase family) and AGE-R2 (substrate of protein kinase C) have been found in neurons, while AGE-R3 is restricted to glia. The present study investigates which of these receptors may be responsible for binding AGEs in the NF conglomerates of motoneurons. Immunostaining of paraffin sections from eight ALS patients (five sporadic and three familial) and three control cases was performed with antibodies directed against R1 and R2, in parallel with those against AGEs and SOD1. The sites of AGE-R1 immunoreactivity (IR) in motoneurons were in conformity to those of NF-associated AGE and SOD1 IRs. By contrast, the IR of R2 was negative in NF conglomerates. Negative R2 IR for NF conglomerates was outlined by surrounding coarse R2 immunopositive granules in the perikaryon. No IR for R1 or R2 was found in hyaline or Bunina inclusions. There was no extraneuronal expression of IR for AGE-R1 or AGEs in microglia or astroglia around the NF accumulation. The colocalization of AGE, AGE-R1, and SOD1 at NF conglomerates in motoneurons supports the notion that AGE-mediated oxidative stress and protein aggregation may be implicated in NF conglomeration and ALS pathogenesis.

Serpin=serine protease-like complexes within neurofilament conglomerates of motoneurons in amyotrophic lateral sclerosis.

Neurofilamentous conglomerates (NfCg), as axonal spheroids or conglomerates in motoneurons, are the histopathologic hallmarks for early stages of amyotrophic lateral sclerosis (ALS). We hypothesize that NfCg may be formed by post-translational modifications of altered Nf proteins that include: (1) hyperphosphorylation, (2) glycosylation (or glycoxidation), (3) nitration, (4) ubiquitination and/or (5) crosslinking by the Ca++-dependent transglutaminase (TGase). These, as well as other changes, are predicted to be initiated or accentuated by oxidative damage. The damaged Nf proteins then activate cascades of intracellular protein degradation which include ATP-dependent ubiquitin/proteasome proteolysis. Other proteolytic systems, either Ca++-dependent or independent, may also be activated, such as serine and cysteine protease systems. These enzymes, either lysosomal or non-lysosomal may also participate in the degradation of damaged Nf proteins being balanced by their cognate inhibitors. Protein complexes formed by these protease=inhibitor systems, along with damaged Nf proteins, may accumulate within the cell bodies as neuronal inclusions, since a number of intracellular inclusions are found in motor neurons in ALS. In the current study, we investigated the involvement of serine proteases and their serpins in NfCg formation. Pairs of three serine proteases (trypsin, chymotrypsin and thrombin) and their cognate serpins (alpha1-anti-trypsin, alpha1-anti-chymotrypsin, and protease nexin I) were probed in motoneurons with their antibodies for both NfCg and inclusions. Positive immunoreactivities for all serine proteases and their cognate serpins support the contention that the imbalance of serine proteases and internalized serpins may have a role in formation of NfCg and inclusions, and hence, the pathogenesis of ALS.

Advanced glycation endproducts in neurofilament conglomeration of motoneurons in familial and sporadic amyotrophic lateral sclerosis.

BACKGROUND: Massive neurofilament conglomeration in motor neurons has been described to occur in the early stages of both familial and sporadic amyotrophic lateral sclerosis (ALS). Previously, neurofilament conglomerates were immunolabeled for both superoxide dismutase (SOD1) and nitrotyrosine, suggesting the potential for oxidative nitration damage to neurofilament protein by peroxynitrite. Long-lived neurofilaments may also undergo modification by advanced glycation endproducts (AGEs) with concomitant generation of free radicals, including superoxide. This radical species may then react with nitric oxide to form the potent oxidant, peroxynitrite, which in turn can nitrate neurofilament protein. Such a glycated and nitrated neurofilament protein may become resistant to proteolytic systems, forming high-molecular-weight protein complexes and cytotoxic, neuronal inclusions. MATERIALS AND METHODS: Paraffin sections containing both neurofilament conglomerates and neuronal inclusions were obtained from patients with sporadic (n = 5) and familial (n = 2) ALS and were probed with specific antibodies directed against the AGEs cypentodine/piperidine-enolone, arginine-lysine imidazole, pentosidine, and pyrraline. RESULTS: Neurofilament conglomerates, but not neuronal inclusions, were intensely immunolabeled with each of the anti-AGE antibodies tested. The immunoreactivity was selective for neurofilament conglomerates and suggested that AGEs may form inter- or intramolecular cross-links in neurofilament proteins. CONCLUSIONS: These data support the hypothesis that AGE formation affects neurofilament proteins in vivo and is associated with the concomitant induction of SODI and protein nitration in neurofilament conglomerates. AGE formation in neurofilament protein may not only cause covalent cross-linking but also generate superoxide and block nitric oxide-mediated responses, thereby perpetuating neuronal toxicity in patients with ALS.

Neuropathology of amyotrophic lateral sclerosis: new perspectives on an old disease.

Recent discoveries on linkage of the gene mutation of an enzyme, copper/zinc superoxide dismutase 1 (SOD-1), to familial amyotrophic lateral sclerosis (ALS) (which constitutes about 1% of all ALS cases) and several transgenic mouse models of ALS have shed light on potential pathogenetic processes involved in this disease. Any speculation as to the pathogenesis of ALS must reflect the unique neurobiology of motor neurons. The most distinctive aspects of motor neurons are their asymmetry, large size, and enormously elongated and thick axons. These characteristics also contribute to their vulnerability to ALS. The determinants of these unique properties are the intermediate cytoskeletal filaments, and the neurofilaments of motor neurons. This characteristic is not exclusive to motor neurons and is shared with other neurons with long axons, including some sensory neurons that are also involved in ALS. The histopathology of the early stages of ALS overwhelmingly suggests that accumulation and aggregation of neurofilaments within motor neurons is intimately related to the morphogenesis of the unique cytoplasmic inclusions, and plays a central role in the pathogenesis of the disease. Understanding of the causal relationship and the morphogenesis of inclusion bodies is critical in any attempt to reverse this complex disease process, which potentially involves the neurotoxic effects of free radicals (nitric oxide, superoxide, hydrogen peroxide, and peroxynitrite, etc) on neurofilaments. By emphasizing the unique make-up of motor neurons, this review intends to reevaluate and reinterpret the basic neuropathology of ALS in the light of recent molecular genetic-data.

Aberrant glycosylation/phosphorylation in chromatolytic motoneurons of Werdnig-Hoffmann disease.

Chromatolytic motor neurons (cMN) in Werdnig-Hoffmann disease (WHD) were investigated in both spinal anterior horns and hypoglossal nuclei with both immuno- and lectin-histochemistry in six cases (3-9 months; two female and four male) of clinically typical WHD. Most characteristic findings from lectin-histochemistry were central accumulation of N-linked glycopeptides and marked general paucity of O-linked glycopeptides in cMN. Phosphorylated intermediate filaments, developmentally regulated cytoskeletons and cell adhesion molecules were abundant at the periphery of cMN, as visualized with immunohistochemistry. Both N-linked and O-linked glycoproteins were reciprocally absent or scarce at the peripheral zone of cMN. This intriguing phenomenon provided the basis for postulating the pathogenesis of WHD. The reciprocal ('yen-yang') dissociation of phosphorylation and glycosylation of neurofilament proteins was only seen with phosphorylated neurofilaments and seen only in cMN, not in the control or surrounding unaffected motoneurons. The central accumulation of N-linked glycopeptides was in contrast with peripheral absence of O-GlcNAc-linked glycopeptides which would normally be expected to colocalize with phosphorylated neurofilaments. Both O-glycosylation and phosphorylation are considered essential for assembly and network of neurofilaments. Aberrant O-glycosylation and dissociation of O-glycosylation/phosphorylation would not only cause a defect in neurofilament assembly but also neuron-glia adhesion (via a molecule such as Ng-CAM), causing a failure of lower motoneurons to synapse homophilically with the upper motoneurons and also a failure to adhere heterophilically to glia, resulting in the histopathologic tetrad ((i) central chromatolysis, (ii) empty-cell beds, (iii) migratory motoneurons and (iv) glial bundles of spinal roots) typical of WHD.

Role of SOD-1 and nitric oxide/cyclic GMP cascade on neurofilament aggregation in ALS/MND.

A number of free radicals such as superoxide and nitric oxide may cause damage to motor neurons but the exact mechanism remains to be elucidated. A potent free radical, peroxynitrite, is readily formed from superoxide and nitric oxide, which captures superoxide three times faster than SOD-1. Peroxynitrite may nitrate tyrosine residues of light neurofilaments (NF-I), thereby altering NF assembly and causing NF accumulation in motor neurons. To test this hypothesis we have probed the massive NF aggregates which are histopathological hallmarks of ALS/MND with immunohistochemistry. We investigated localization of reaction products related to SOD-1, nitric oxide synthase (NOS) and cyclic GMP activities. Our studies show colocalization of NF aggregates with SOD-1/b-NOS/calmodulin /citrulline/cGMP and nitrotyrosine in upper motor neuron conglomerates (Cgl) and lower motor neutron axonal spheroids (Axs). This strongly supports the notion that peroxynitrite deranges NF phosphorylation and assembly, by nitrating tyrosine residues in NF-L. Impaired phosphorylation of NF subunits, either at NF-I or at NF-H, may affect the slow axonal transport culminating in proximo-distal accumulation of NF and slowly progressive motoneuron death.

Colocalization of NOS and SOD1 in neurofilament accumulation within motor neurons of amyotrophic lateral sclerosis: an immunohistochemical study.

Peroxynitrite, formed from nitric oxide and superoxide, may affect neurofilament assembly and cause neurofilament accumulation in motoneurons. This hypothesis may reconcile the mutations of two genes: superoxide dismutase-1 in some patients with familial amyotrophic lateral sclerosis, and the gene for the heavy neurofilament in some patients with sporadic amyotrophic lateral sclerosis previously reported. We found colocalization of superoxide dismutase-1 and nitric oxide synthase in the foci of neurofilament accumulation as 'conglomerates' in upper motor neurons and 'axonal spheroids' in lower motor neurons. In addition, all the specific molecules related to the reactions, including calmodulin, 3', 5'-cyclic guanosine-monophosphate, citrulline, and nitrotyrosine were found strongly immunopositive in the site of neurofilament accumulation. Our data support the view that the neurofilament aggregates are tightly linked with superoxide dismutase-1 and nitric oxide synthase activities. Both enzymes may focally contribute to peroxynitrite formation at light neurofilament, which is rich in both tyrosine and arginine residues and hence considered as the vulnerable site for nitrotyrosine formation. Nitrotyrosine is known to inhibit phosphorylation and if it impairs phosphorylation of neurofilament subunits, either light or heavy, may alter the slow axonal transport culminating in proximo-distal accumulation of NF and slowly progressive motoneuron death.

Inclusion body myositis.

IBM remains a poorly understood form of idiopathic inflammatory myopathy, although great progress in the areas of clinical recognition and pathophysiology have been made recently. The question of whether therapy can favorably influence short- and/or long-term outcome is still unanswered. Several recent reports suggest some possibility of at least slowing progression with immunosuppressive therapy. Long-term therapeutic trials with goals that include stabilization, rather than improvements in strength, are urgently needed.