The effect of tread patterns on slip resistance of footwear outsoles based on composite materials in icy conditions.

INTRODUCTION: Falls on icy surfaces are the leading cause of injuries for outdoor workers. Footwear outsole material and geometrical design parameters are the most significant factors affecting slips-and-falls. Recently, composite materials have been incorporated into outsoles to improve traction, yet the best design parameters are not fully understood. METHOD: In this effort, based on Taguchi orthogonal array design, 27 outsole prototypes were fabricated with different tread pattern features using our patented composites and tested in a simulated winter condition. RESULTS: An analysis of variance (ANOVA) showed that surface area (p = 0.041, Contribution = 15.63%) was the only factor significantly affecting the slip-resistance of our prototypes. The best performance was observed for the maximized surface area covered by our composite material with circular and half circular plugs laid obliquely, mostly in the forefoot area. PRACTICAL APPLICATIONS: These findings suggest that some tread design features of composite-based footwear have a great role in affecting slip-resistance properties of composite-based footwear.

Biomechanical effects of different loads and constraints on finite element modeling of the humerus.

Currently, there is no established finite element (FE) method to apply physiologically realistic loads and constraints to the humerus. This FE study showed that 2 'simple' methods involving direct head loads, no head constraints, and rigid elbow or mid-length constraints created excessive stresses and bending. However, 2 'intermediate' methods involving direct head loads, but flexible head and elbow constraints, produced lower stresses and bending. Also, 2 'complex' methods involving muscles to generate head loads, plus flexible head and elbow constraints, generated the lowest stresses and moderate bending. This has implications for FE modeling research on intact and implanted humeri.

Biomechanical design optimization of distal femur locked plates: A review.

Clinical findings, manufacturer instructions, and surgeon's preferences often dictate the implantation of distal femur locked plates (DFLPs), but healing problems and implant failures still persist. Also, most biomechanical researchers compare a particular DFLP configuration to implants like plates and nails. However, this begs the question: Is this specific DFLP configuration biomechanically optimal to encourage early callus formation, reduce bone and implant failure, and minimize bone "stress shielding"? Consequently, it is crucial to optimize, or characterize, the biomechanical performance (stiffness, strength, fracture micro-motion, bone stress, plate stress) of DFLPs influenced by plate variables (geometry, position, material) and screw variables (distribution, size, number, angle, material). Thus, this article reviews 20 years of biomechanical design optimization studies on DFLPs. As such, Google Scholar and PubMed websites were searched for articles in English published since 2000 using the terms "distal femur plates" or "supracondylar femur plates" plus "biomechanics/biomechanical" and "locked/locking," followed by searching article reference lists. Key numerical outcomes and common trends were identified, such as: (a) plate cross-sectional area moment of inertia can be enlarged to lower plate stress at the fracture; (b) plate material has a larger influence on plate stress than plate thickness, buttress screws, and inserts for empty plate holes; (c) screw distribution has a major influence on fracture micro-motion, etc. Recommendations for future work and clinical implications are then provided, such as: (a) simultaneously optimizing fracture micro-motion for early healing, reducing bone and implant stresses to prevent re-injury, lowering "stress shielding" to avoid bone resorption, and ensuring adequate fatigue life; (b) examining alternate non-metallic materials for plates and screws; (c) assessing the influence of condylar screw number, distribution, and angulation, etc. This information can benefit biomedical engineers in designing or evaluating DFLPs, as well as orthopedic surgeons in choosing the best DFLPs for their patients.

A 20-Year Review of Biomechanical Experimental Studies on Spine Implants Used for Percutaneous Surgical Repair of Vertebral Compression Fractures.

A vertebral compression fracture (VCF) is an injury to a vertebra of the spine affecting the cortical walls and/or middle cancellous section. The most common risk factor for a VCF is osteoporosis, thus predisposing the elderly and postmenopausal women to this injury. Clinical consequences include loss of vertebral height, kyphotic deformity, altered stance, back pain, reduced mobility, reduced abdominal space, and reduced thoracic space, as well as early mortality. To restore vertebral mechanical stability, overall spine function, and patient quality of life, the original percutaneous surgical intervention has been vertebroplasty, whereby bone cement is injected into the affected vertebra. Because vertebroplasty cannot fully restore vertebral height, newer surgical techniques have been developed, such as kyphoplasty, stents, jacks, coils, and cubes. But, relatively few studies have experimentally assessed the biomechanical performance of these newer procedures. This article reviews over 20 years of scientific literature that has experimentally evaluated the biomechanics of percutaneous VCF repair methods. Specifically, this article describes the basic operating principles of the repair methods, the study protocols used to experimentally assess their biomechanical performance, and the actual biomechanical data measured, as well as giving a number of recommendations for future research directions.

The effect of wear on slip-resistance of winter footwear with composite outsoles: A pilot study.

Falls on icy surfaces are among the top causes of injuries for workers exposed to the outdoor environment. Our recent field study showed that a new generation of winter footwear incorporating composite outsoles was able to reduce slips and falls on icy surfaces by 68% and 78%, respectively. The widespread adoption of this type of footwear may lead to substantial reductions in pain, suffering and costs of fall-related injuries. However, these composite materials are sensitive to wear and abrasion, which makes it likely that their slip-resistance performance may degrade with use. The goal of this pilot study was to determine the extent to which the slip-resistance of two types of winter footwear with composite outsoles changed as they wore down with real-world use. Seven participants were recruited for this study and were asked to walk 100K steps with their assigned footwear. Tread depth and slip-resistance performance (using the Maximum Achievable Angle test) were measured at baseline and again after each 25K-step interval up to 100K. Our results showed that the slip-resistance performance of the test footwear dropped significantly after the 75K and 100K step intervals compared to baseline. In addition, significant changes in tread depth were found after only 25K steps. These findings indicate that the performance of this type of footwear degrades relatively quickly with real-world use. Therefore, larger scale study of the slip-resistance of winter footwear with composite outsoles is needed and members of the public should be made aware of the potential loss of slip-resistance of these products.

Biomechanical analysis of fixation methods for acetabular fractures: A review.

Acetabular fractures are known as one of the most frequent types of pelvic fractures with growing frequency among elderly people. Because of this, it is important to establish the methods of repair that will produce optimal outcomes for fracture healing and joint remobilization. Open reduction and internal fixation are considered as the "gold standard" of acetabular fracture repair; however, to the best of authors' knowledge, there is no systematic review comparing different repair methods from biomechanical point of view. As such, in this review paper, we summarize the results of English language literature biomechanically focused on acetabular fracture fixation methods in the last thirty years with the aim to create a reference for clinical decision making. The selected literature within the review is broken down into categories based on type of fracture, i.e., simple or complex, and then further grouped based on fracture line orientation. Clinical recommendations and future research possibilities are also provided.

Reducing fall risk for home care workers with slip resistant winter footwear.

Falls on icy surfaces are the leading cause of occupational injuries for workers exposed to outdoor winter conditions. Slip resistant footwear has been shown to reduce the risk of falls for indoor workers but until recently, there was no accepted standard for evaluating the slip resistance of winter footwear on icy surfaces. Our team recently developed a lab-based testing protocol for measuring footwear slip resistance. This protocol, called the Maximum Achievable Angle (MAA) test, measures the steepest ice-covered slope that participants can walk up and down without experiencing a slip in a simulated winter environment. This lab-based protocol has found there is wide variability in the performance of commercially available winter footwear. In particular, we have found that a new generation of footwear that incorporates composite materials in the outsole, performs much better than most other footwear. The objective of this project was to investigate whether the footwear that performed well in our lab-based testing would reduce the risk of slips and/or falls in real-world winter conditions. One hundred and ten home healthcare workers from SE Health were recruited for this study and were asked to report their exposure to icy surfaces along with the numbers of slips and numbers of falls they experienced each week using online surveys over eight weeks in the winter. Fifty participants (the intervention group) were provided winter footwear that were among the best performing in the MAA test. The remaining sixty participants (the control group) wore their own footwear for the duration of the study. A total of 563 slips and 36 falls were reported over the eight-week data collection period. The intervention group consistently reported fewer slips (127 vs 436) and fewer falls (6 vs 30) compared to the control group. We found the slip rate in the intervention group was between 68.0% and 68.7% lower than the control group. Similarly, the fall rate was between 78.5% and 81.5% lower in the intervention group compared to the control group. These findings demonstrate that footwear that performs well in the MAA test can reduce the risk of both slips and falls in real-world winter conditions.

Effect of Exercise Training on Heart Rate Variability in Patients with Heart Failure After Percutaneous Coronary Intervention.

BACKGROUND: This study aims to evaluate the effect of exercise training on heart rate variability (HRV) and to determine the correlation between parameters of HRV and the ejection fraction in patients with heart failure after percutaneous coronary intervention. MATERIAL AND METHODS: Fifty patients with left ventricular ejection fraction ≤ 40% undergone percutaneous coronary intervention were randomly allocated in either an exercise training (ET) group or a control group. The ET group performed exercise training for 45 minutes, three times a week for seven weeks. Patients in both groups received a leaflet for daily exercising at home. HRV parameters comprising, the standard deviation of normal R-R intervals (SDNN), the square root of the mean of the squares of successive R-R intervals differences (RMSSD) ,the percentage of successive R-R intervals differing from more than 50 ms (PNN50), using 24-hour Holter electrocardiographic monitoring was measured. RESULTS: After the intervention, the SDNN improved in the ET group (P=0.002), while changes in all remaining HRV indices were insignificant (P≥0.05). The control group showed no significant changes in any HRV parameters (P≥0.05). Changes in SDNN in the ET group were significantly different from the control group (P=0.003). At baseline, our results revealed a significant weak correlation between ejection fraction and SDNN (r =0.279, P=0.047). However, ejection fraction did not correlate significantly with RMSSD and PNN50. CONCLUSION: Exercise training is safe and feasible in post percutaneous coronary intervention patients, even in those with reduced ejection fraction. In a seven-week period, exercise training was effective in improving HRV in heart failure patients after percutaneous coronary intervention.

Slip resistance and wearability of safety footwear used on icy surfaces for outdoor municipal workers.

BACKGROUND: Outdoor workers experience high injury rates in the winter due to slipping on ice and snow. Our testing program has demonstrated that most safety footwear does not provide adequate slip-resistance and/or comfort in icy conditions. OBJECTIVE: Our objective was to determine which of the most commonly worn safety footwear available to outdoor municipal workers in Toronto, Ontario, Canada would best prevent slips on icy surfaces and which models had good wearability. METHODS: We selected 45 of the most popular types of winter footwear worn by these workers and applied our Maximum Achievable Angle (MAA) test method to rate the slip-resistance of the footwear. A ten-point rating scale was used for recording participants' perceptions of wearability. The MAA test measured the steepest ice-covered incline that participants can walk up and down without experiencing a slip. RESULTS: Of the 45 types of footwear tested, only one model achieved an MAA score of 8 degrees that exceeded our cut-off for acceptable performance set at 7 degrees. Secondary measures of performance including thermal insulation; wearability and heaviness of footwear tested were also ranked. CONCLUSION: Our results demonstrate that footwear manufactures have the opportunity to differentiate their footwear by investing in slip-resistant outsole materials.

Biomechanical Analysis Using FEA and Experiments of Metal Plate and Bone Strut Repair of a Femur Midshaft Segmental Defect.

This investigation assessed the biomechanical performance of the metal plate and bone strut technique for fixing recalcitrant nonunions of femur midshaft segmental defects, which has not been systematically done before. A finite element (FE) model was developed and then validated by experiments with the femur in 15 deg of adduction at a subclinical hip force of 1 kN. Then, FE analysis was done with the femur in 15 deg of adduction at a hip force of 3 kN representing about 4 x body weight for a 75 kg person to examine clinically relevant cases, such as an intact femur plus 8 different combinations of a lateral metal plate of fixed length, a medial bone strut of varying length, and varying numbers and locations of screws to secure the plate and strut around a midshaft defect. Using the traditional "high stiffness" femur-implant construct criterion, the repair technique using both a lateral plate and a medial strut fixed with the maximum possible number of screws would be the most desirable since it had the highest stiffness (1948 N/mm); moreover, this produced a peak femur cortical Von Mises stress (92 MPa) which was below the ultimate tensile strength of cortical bone. Conversely, using the more modern "low stiffness" femur-implant construct criterion, the repair technique using only a lateral plate but no medial strut provided the lowest stiffness (606 N/mm), which could potentially permit more in-line interfragmentary motion (i.e., perpendicular to the fracture gap, but in the direction of the femur shaft long axis) to enhance callus formation for secondary-type fracture healing; however, this also generated a peak femur cortical Von Mises stress (171 MPa) which was above the ultimate tensile strength of cortical bone.

Does High Frequency Transcutaneous Electrical Nerve Stimulation (TENS) Affect EEG Gamma Band Activity?

BACKGROUND: Transcutaneous electrical nerve stimulation (TENS) is a noninvasive, inexpensive and safe analgesic technique used for relieving acute and chronic pain. However, despite all these advantages, there has been very little research into the therapeutic effects of TENS on brain activity. To the best of our knowledge, there is no evidence on the effect of high frequency TENS on the gamma band activity. OBJECTIVE: Investigation of the effect of high frequency TENS on the electroencephalographic (EEG) gamma band activity after inducing ischemic pain in healthy volunteers is considered. MATERIAL AND METHODS: The modified version of Submaximal effort tourniquet test was carried out to induce tonic pain in 15 right-handed healthy volunteers. The high frequency TENS (150µs in duration, frequency of 100 Hz) was applied for 20 minutes. Pain intensity was assessed at using Visual Analog Scale (VAS) in two conditions (after-pain, after-TENS). EEG gamma band activity was recorded by a 19-channel EEG in three conditions (baseline, after-pain and after- TENS). The repeated measure ANOVA and paired-sample T- tests were used for data analysis. RESULTS: EEG analysis showed an increase in gamma total power after inducing pain as compared to baseline and a decrease after the application of TENS (mean±SD: .043±.029 to .088±.042 to .038±.022 µV2 ).The analysis of VAS values demonstrated that the intensity of induced pain (mean±SD: 51.53±9.86) decreased after the application of TENS (mean±SD: 18.66±10.28). All these differences were statistically significant (p<.001). CONCLUSION: The results of this study revealed that the high frequency TENS can reduce the enhanced gamma band activity after the induction of tonic pain in healthy volunteers. This finding might help as a functional brain biomarker which could be useful for pain treatment, specifically for EEG-based neurofeedback approaches.

Mechanical characterization of structurally porous biomaterials built via additive manufacturing: experiments, predictive models, and design maps for load-bearing bone replacement implants.

Porous biomaterials can be additively manufactured with micro-architecture tailored to satisfy the stringent mechano-biological requirements imposed by bone replacement implants. In a previous investigation, we introduced structurally porous biomaterials, featuring strength five times stronger than commercially available porous materials, and confirmed their bone ingrowth capability in an in vivo canine model. While encouraging, the manufactured biomaterials showed geometric mismatches between their internal porous architecture and that of its as-designed counterpart, as well as discrepancies between predicted and tested mechanical properties, issues not fully elucidated. In this work, we propose a systematic approach integrating computed tomography, mechanical testing, and statistical analysis of geometric imperfections to generate statistical based numerical models of high-strength additively manufactured porous biomaterials. The method is used to develop morphology and mechanical maps that illustrate the role played by pore size, porosity, strut thickness, and topology on the relations governing their elastic modulus and compressive yield strength. Overall, there are mismatches between the mechanical properties of ideal-geometry models and as-manufactured porous biomaterials with average errors of 49% and 41% respectively for compressive elastic modulus and yield strength. The proposed methodology gives more accurate predictions for the compressive stiffness and the compressive strength properties with a reduction of the average error to 11% and 7.6%. The implications of the results and the methodology here introduced are discussed in the relevant biomechanical and clinical context, with insight that highlights promises and limitations of additively manufactured porous biomaterials for load-bearing bone replacement implants. STATEMENT OF SIGNIFICANCE: In this work, we perform mechanical characterization of load-bearing porous biomaterials for bone replacement over their entire design space. Results capture the shift in geometry and mechanical properties between as-designed and as-manufactured biomaterials induced by additive manufacturing. Characterization of this shift is crucial to ensure appropriate manufacturing of bone replacement implants that enable biological fixation through bone ingrowth as well as mechanical property harmonization with the native bone tissue. In addition, we propose a method to include manufacturing imperfections in the numerical models that can reduce the discrepancy between predicted and tested properties. The results give insight into the use of structurally porous biomaterials for the design and additive fabrication of load-bearing implants for bone replacement.

Cross-cultural measurement invariance of the Revised Child Anxiety and Depression Scale across 11 world-wide societies.

BACKGROUND: In order to compare estimates by one assessment scale across various cultures/ethnic groups, an important aspect that needs to be demonstrated is that its construct across these groups is invariant when measured using a similar and simultaneous approach (i.e., demonstrated cross-cultural measurement invariance). One of the methods for evaluating measurement invariance is testing for differential item functioning (DIF), which assesses whether different groups respond differently to particular items. The aim of this study was to evaluate the cross-cultural measurement invariance of the Revised Child Anxiety and Depression Scale (RCADS) in societies with different socioeconomic, cultural, and religious backgrounds. METHODS: The study was organised by the International Child Mental Health Study Group. Self-reported data were collected from adolescents residing in 11 countries: Brazil, Bulgaria, Croatia, Indonesia, Montenegro, Nigeria, Palestinian Territories, the Philippines, Portugal, Romania and Serbia. The multiple-indicators multiple-causes model was used to test the RCADS items for DIF across the countries. RESULTS: Ten items exhibited DIF considering all cross-country comparisons. Only one or two items were flagged with DIF in the head-to-head comparisons, while there were three to five items flagged with DIF, when one country was compared with the others. Even with all cross-culturally non-invariant items removed from nine language versions tested, the original factor model representing six anxiety and depressive symptoms subscales was not significantly violated. CONCLUSIONS: There is clear evidence that relatively small number of the RCADS items is non-invariant, especially when comparing two different cultural/ethnic groups, which indicates on its sound cross-cultural validity and suitability for cross-cultural comparisons in adolescent anxiety and depressive symptoms.