Eccentric knee-flexor strength and risk of hamstring injuries in Rugby Union: A prospective study

BACKGROUND Hamstring strain injuries (HSIs) represent the most common cause of lost playing time in rugby union. Eccentric knee-flexor weakness and between-limb imbalance in eccentric knee-flexor strength are associated with a heightened risk of hamstring injury in other sports; however these variables have not been explored in rugby union. PURPOSE To determine if lower levels of eccentric knee-flexor strength or greater between-limb imbalance in this parameter during the Nordic hamstring exercise are risk-factors for hamstring strain injury in rugby union. STUDY DESIGN Cohort study; level of evidence, 3. METHODS This prospective study was conducted over the 2014 Super Rugby and Queensland Rugby Union seasons. In total, 178 rugby union players (age, 22.6 ± 3.8 years; height, 185 ± 6.8 cm; mass, 96.5 ± 13.1 kg) had their eccentric knee-flexor strength assessed using a custom-made device during the pre-season. Reports of previous hamstring, quadriceps, groin, calf and anterior cruciate ligament injury were also obtained. The main outcome measure was prospective occurrence of hamstring strain injury. RESULTS Twenty players suffered at least one hamstring strain during the study period. Players with a history of hamstring strain injury had 4.1 fold (RR = 4.1, 95% CI = 1.9 to 8.9, p = 0.001) greater risk of subsequent hamstring injury than players without such history. Between-limb imbalance in eccentric knee-flexor strength of ≥ 15% and ≥ 20% increased the risk of hamstring strain injury 2.4 fold (RR = 2.4, 95% CI = 1.1 to 5.5, p = 0.033) and 3.4 fold (RR = 3.4, 95% CI = 1.5 to 7.6, p = 0.003), respectively. Lower eccentric knee flexor strength and other prior injuries were not associated with increased risk of future hamstring strain. Multivariate logistic regression revealed that the risk of re-injury was augmented in players with strength imbalances. CONCLUSION Previous hamstring strain injury and between-limb imbalance in eccentric knee-flexor strength were associated with an increased risk of future hamstring strain injury in rugby union. These results support the rationale for reducing imbalance, particularly in players who have suffered a prior hamstring injury, to mitigate the risk of future injury.

WNT16 influences bone mineral density, cortical bone thickness, bone strength, and osteoporotic fracture risk

We aimed to identify genetic variants associated with cortical bone thickness (CBT) and bone mineral density (BMD) by performing two separate genome-wide association study (GWAS) meta-analyses for CBT in 3 cohorts comprising 5,878 European subjects and for BMD in 5 cohorts comprising 5,672 individuals. We then assessed selected single-nucleotide polymorphisms (SNPs) for osteoporotic fracture in 2,023 cases and 3,740 controls. Association with CBT and forearm BMD was tested for ~2.5 million SNPs in each cohort separately, and results were meta-analyzed using fixed effect meta-analysis. We identified a missense SNP (Thr>Ile; rs2707466) located in the WNT16 gene (7q31), associated with CBT (effect size of -0.11 standard deviations [SD] per C allele, P = 6.2×10-9). This SNP, as well as another nonsynonymous SNP rs2908004 (Gly>Arg), also had genome-wide significant association with forearm BMD (-0.14 SD per C allele, P = 2.3×10-12, and -0.16 SD per G allele, P = 1.2×10-15, respectively). Four genome-wide significant SNPs arising from BMD meta-analysis were tested for association with forearm fracture. SNP rs7776725 in FAM3C, a gene adjacent to WNT16, was associated with a genome-wide significant increased risk of forearm fracture (OR = 1.33, P = 7.3×10-9), with genome-wide suggestive signals from the two missense variants in WNT16 (rs2908004: OR = 1.22, P = 4.9×10-6 and rs2707466: OR = 1.22, P = 7.2×10-6). We next generated a homozygous mouse with targeted disruption of Wnt16. Female Wnt16-/- mice had 27% (P<0.001) thinner cortical bones at the femur midshaft, and bone strength measures were reduced between 43%-61% (6.5×10-13<P<5.9×10-4) at both femur and tibia, compared with their wild-type littermates. Natural variation in humans and targeted disruption in mice demonstrate that WNT16 is an important determinant of CBT, BMD, bone strength, and risk of fracture. © 2012 Zheng et al.

Enhanced chondrogenesis of human nasal septum derived progenitors on nanofibrous scaffolds

Topographical cues can be exploited to regulate stem cell attachment, proliferation, differentiation and function in vitro and in vivo. In this study, we aimed to investigate the influence of different nanofibrous topographies on the chondrogenic differentiation potential of nasal septum derived progenitors (NSP) in vitro. Aligned and randomly oriented Ploy (L-lactide) (PLLA)/Polycaprolactone (PCL) hybrid scaffolds were fabricated via electrospinning. First, scaffolds were fully characterized, and then NSP were seeded on them to study their capacity to support stem cell attachment, proliferation and chondrogenic differentiation. Compared to randomly oriented nanofibers, aligned scaffolds showed a high degree of nanofiber alignment with much better tensile strength properties. Both scaffolds supported NSP adhesion, proliferation and chondrogenic differentiation. Despite the higher rate of cell proliferation on random scaffolds, a better chondrogenic differentiation was observed on aligned nanofibers as deduced from higher expression of chondrogenic markers such as collagen type II and aggrecan on aligned scaffolds. These findings demonstrate that electrospun constructs maintain NSP proliferation and differentiation, and that the aligned nanofibrous scaffolds can significantly enhance chondrogenic differentiation of nasal septum derived progenitors

Analysis of focal adhesion turnover: A quantitative live-cell imaging example

Recent advances in optical and fluorescent protein technology have rapidly raised expectations in cell biology, allowing quantitative insights into dynamic intracellular processes like never before. However, quantitative live-cell imaging comes with many challenges including how best to translate dynamic microscopy data into numerical outputs that can be used to make meaningful comparisons rather than relying on representative data sets. Here, we use analysis of focal adhesion turnover dynamics as a straightforward specific example on how to image, measure, and analyze intracellular protein dynamics, but we believe this outlines a thought process and can provide guidance on how to understand dynamic microcopy data of other intracellular structures.

Biceps femoris architecture and strength in athletes with a prior ACL reconstruction

Purpose To determine if limbs with a history of anterior cruciate ligament (ACL) injury reconstructed from the semitendinosus (ST) display different biceps femoris long head (BFlh) architecture and eccentric strength, assessed during the Nordic hamstring exercise, compared to the contralateral uninjured limb. Methods The architectural characteristics of the BFlh were assessed at rest and at 25% of a maximal voluntary isometric contraction (MVIC) in the control (n=52) and previous ACL injury group (n=15) using two-dimensional ultrasonography. Eccentric knee-flexor strength was assessed during the Nordic hamstring exercise. Results Fascicle length was shorter (p=0.001; d range: 0.90 to 1.31) and pennation angle (p range: 0.001 to 0.006: d range: 0.87 to 0.93) was greater in the BFlh of the ACL injured limb when compared to the contralateral uninjured limb at rest and during 25% of MVIC. Eccentric strength was significantly lower in the ACL injured limb than the contralateral uninjured limb (-13.7%; -42.9N; 95% CI = -78.7 to -7.2; p=0.021; d=0.51). Fascicle length, MVIC and eccentric strength were not different between the left and right limb in the control group. Conclusions Limbs with a history of ACL injury reconstructed from the ST have shorter fascicles and greater pennation angles in the BFlh compared to the contralateral uninjured side. Eccentric strength during the Nordic hamstring exercise of the ACL injured limb is significantly lower than the contralateral side. These findings have implications for ACL rehabilitation and hamstring injury prevention practices which should consider altered architectural characteristics.

Direct shear testing on unsaturated silty soils to investigate the effects of drying and wetting on shear strength parameters at low suction

A modified conventional direct shear device was used to measure unsaturated shear strength of two silty soils at low suction values (0 ~ 50 kPa) that were achieved by following drying and wetting paths of soil water characteristic curves (SWCCs). The results revealed that the internal friction angle of the soils was not significantly affected by either the suction or the drying wetting SWCCs. The apparent cohesion of soil increased with a decreasing rate as suction increased. Shear stress-shear displacement curves obtained from soil specimens subjected to the same net normal stress and different suction values showed a higher initial stiffness and a greater peak stress as suction increased. A soil in wetting exhibited slightly higher peak shear stress and more contractive volume change behavior than that of soil in drying at the same net normal stress and suction.

A comparison of training methods to increase neck muscle strength

Objective To compare two neck strength training modalities. Background Neck injury in pilots flying high performance aircraft is a concern in aviation medicine. Strength training may be an effective means to strengthen the neck and decrease injury risk. Methods The cohort consisted of 32 age-height-weight matched participants, divided into two experimental groups; the Multi-Cervical Unit (MCU) and Thera-Band tubing groups (THER), and a control (CTRL) group. Ten weeks of training were undertaken and pre-and post isometric strength testing for all groups was performed on the MCU. Comparisons between the three groups were made using a Kruskal-Wallis test and effect sizes between the MCU and the THER groups and the THER and CTRL groups were also calculated. Results The MCU group displayed the greatest increase in isometric strength (flexion 64.4%, extension 62.9%, left lateral flexion 53.3%, right lateral flexion 49.1%) and differences were only statistically significant (p<0.05) when compared to the CTRL group. Increases in neck strength for the THER group were lower than that shown in the MCU group (flexion 42.0%, extension 29.9%, left lateral flexion 26.7%, right lateral flexion 24.1%). Moderate to large effect sizes were found between the MCU and THER as well as the THER and CTRL groups. Conclusions This study demonstrated that the MCU was the most effective training modality to increase isometric cervical muscle strength. Thera-Band tubing did however, produce moderate gains in isometric neck strength

Plasma assisted surface modification of organic biopolymers to prevent bacterial attachment

Despite many synthetic biomaterials having physical properties that are comparable or even superior to those of natural body tissues, they frequently fail due to the adverse physiological reactions they cause within the human body, such as infection and inflammation. The surface modification of biomaterials is an economical and effective method by which biocompatibility and biofunctionality can be achieved while preserving the favorable bulk characteristics of the biomaterial, such as strength and inertness. Amongst the numerous surface modification techniques available, plasma surface modification affords device manufacturers a flexible and environmentally friendly process that enables tailoring of the surface morphology, structure, composition, and properties of the material to a specific need. There are a vast range of possible applications of plasma modification in biomaterial applications, however, the focus of this review paper is on processes that can be used to develop surface morphologies and chemical structures for the prevention of adhesion and proliferation of pathogenic bacteria on the surfaces of in-dwelling medical devices. As such, the fundamental principles of bacterial cell attachment and biofilm formation are also discussed. Functional organic plasma polymerised coatings are also discussed for their potential as biosensitive interfaces, connecting inorganic/metallic electronic devices with their physiological environments.

The effect of polyterpenol thin film surfaces on bacterial viability and adhesion

The nanometer scale surface topography of a solid substrate is known to influence the extent of bacterial attachment and their subsequent proliferation to form biofilms. As an extension of our previous work on the development of a novel organic polymer coating for the prevention of growth of medically significant bacteria on three-dimensional solid surfaces, this study examines the effect of surface coating on the adhesion and proliferation tendencies of Staphylococcus aureus and compares to those previously investigated tendencies of Pseudomonas aeruginosa on similar coatings. Radio frequency plasma enhanced chemical vapor deposition was used to coat the surface of the substrate with thin film of terpinen-4-ol, a constituent of tea-tree oil known to inhibit the growth of a broad range of bacteria. The presence of the coating decreased the substrate surface roughness from approximately 2.1 nm to 0.4 nm. Similar to P. aeruginosa, S. aureus presented notably different patterns of attachment in response to the presence of the surface film, where the amount of attachment, extracellular polymeric substance production, and cell proliferation on the coated surface was found to be greatly reduced compared to that obtained on the unmodified surface. This work suggests that the antimicrobial and antifouling coating used in this study could be effectively integrated into medical and other clinically relevant devices to prevent bacterial growth and to minimize bacteria-associated adverse host responses.

Platelet endothelial cell adhesion molecule 1 (PECAM-1) and its interactions with glycosaminoglycans: 2. Biochemical analyses

Platelet endothelial cell adhesion molecule 1 (PECAM-1) (CD31), a member of the immunoglobulin (Ig) superfamily of cell adhesion molecules with six Ig-like domains, has a range of functions, notably its contributions to leukocyte extravasation during inflammation and in maintaining vascular endothelial integrity. Although PECAM-1 is known to mediate cell adhesion by homophilic binding via domain 1, a number of PECAM-1 heterophilic ligands have been proposed. Here, the possibility that heparin and heparan sulfate (HS) are ligands for PECAM-1 was reinvestigated. The extracellular domain of PECAM-1 was expressed first as a fusion protein with the Fc region of human IgG1 fused to domain 6 and second with an N-terminal Flag tag on domain 1 (Flag-PECAM-1). Both proteins bound heparin immobilized on a biosensor chip in surface plasmon resonance (SPR) binding experiments. Binding was pH-sensitive but is easily measured at slightly acidic pH. A series of PECAM-1 domain deletions, prepared in both expression systems, were tested for heparin binding. This revealed that the main heparin-binding site required both domains 2 and 3. Flag-PECAM-1 and a Flag protein containing domains 1-3 bound HS on melanoma cell surfaces, but a Flag protein containing domains 1-2 did not. Heparin oligosaccharides inhibited Flag-PECAM-1 from binding immobilized heparin, with certain structures having greater inhibitory activity than others. Molecular modeling similarly identified the junction of domains 2 and 3 as the heparin-binding site and further revealed the importance of the iduronic acid conformation for binding. PECAM-1 does bind heparin/HS but by a site that is distinct from that required for homophilic binding.

Platelet endothelial cell adhesion molecule 1 (PECAM-1) and its interactions with glycosaminoglycans: 1. Molecular modeling studies

Platelet endothelial cell adhesion molecule 1 (PECAM-1) has many functions, including its roles in leukocyte extravasation as part of the inflammatory response and in the maintenance of vascular integrity through its contribution to endothelial cell−cell adhesion. PECAM-1 has been shown to mediate cell−cell adhesion through homophilic binding events that involve interactions between domain 1 of PECAM-1 molecules on adjacent cells. However, various heterophilic ligands of PECAM-1 have also been proposed. The possible interaction of PECAM-1 with glycosaminoglycans (GAGs) is the focus of this study. The three-dimensional structure of the extracellular immunoglobulin (Ig) domains of PECAM-1 were constructed using homology modeling and threading methods. Potential heparin/heparan sulfate-binding sites were predicted on the basis of their amino acid consensus sequences and a comparison with known structures of sulfate-binding proteins. Heparin and other GAG fragments have been docked to investigate the structural determinants of their protein-binding specificity and selectivity. The modeling has predicted two regions in PECAM-1 that appear to bind heparin oligosaccharides. A high-affinity binding site was located in Ig domains 2 and 3, and evidence for a low-affinity site in Ig domains 5 and 6 was obtained. These GAG-binding regions were distinct from regions involved in PECAM-1 homophilic interactions.

Experimental studies on web crippling strength of hollow flange channels under EOF and IOF load cases

LiteSteel beam (LSB) is a hollow flange channel made from cold-formed steel using a patented manufacturing process involving simultaneous cold-forming and dual electric resistance welding. LSBs are currently used as floor joists and bearers in buildings. However, there are no appropriate design standards available due to its unique hollow flange geometry, residual stress characteristics and initial geometric imperfections arising from manufacturing processes. Recent research studies have focused on investigating the structural behaviour of LSBs under pure bending, predominant shear and combined actions. However, web crippling behaviour and strengths of LSBs still need to be examined. Therefore, an experimental study was undertaken to investigate the web crippling behaviour and strengths of LSBs under EOF (End One Flange) and IOF (Interior One Flange) load cases. A total of 23 web crippling tests were performed and the results were compared with the current AS/NZS 4600 and AISI S100 design standards, which showed that the cold-formed steel design rules predicted the web crippling capacity of LSB sections very conservatively under EOF and IOF load cases. Therefore, suitably improved design equations were proposed to determine the web crippling capacity of LSBs based on experimental results. In addition, new design equations were also developed under the Direct Strength Method format. This paper presents the details of this experimental study on the web crippling behaviour and strengths of LiteSteel beams under EOF and IOF load cases and the results.

Impact resistance and evaluation of retained strength on geotextiles

Over the last few decades, geotextiles have progressively been incorporated into geotechnical applications, especially in the field of coastal engineering. Geotextile materials often act as separator and a filter layer between rocks laid above and subgrade beneath. This versatile material has gradually substituted traditional granular materials because of its ease of installation, consistent quality and labour costefficiency. However, geotextiles often suffer damage during installation due to high dynamic bulk loading of rock placement. This can degrade geotextiles' mechanical strength. The properties considered in this paper include the impact resistance and retained strength of geotextiles. In general, the greater the impact energy applied to geotextiles, the greater the potential for damage. Results highlight the inadequacy of using index derived values as an indicator to determine geotextile performance on site because test results shows that geotextiles (staple fibre (SF) and continuous filament (CF)) with better mechanical properties did not outperform lower mechanical strength materials. The toughest CF product with a CBR index value of 9696N shows inferior impact resistance compared to SF product with the least CBR strength (2719N) given the same impact energy of 9.02 kJ. Test results also indicated that the reduction of strength for CF materials were much greater (between 20 and 50%) compared to SF materials (between 0 and 5%) when subjected to the same impact energy of 4.52 kJ.