Pressure distribution on the anatomic landmarks of the knee and the effect of kneepads

This study examines stress transmitted to anatomic landmarks of the knee (patella, combined patella tendon and tibial tubercle) while in static kneeling postures without kneepads and while wearing two kneepads commonly worn in the mining industry. Ten subjects (7 male, 3 female) simulated postures utilized in low-seam mines: kneeling in full flexion; kneeling at 90° of knee flexion; and kneeling on one knee while in one of three kneepad states (no kneepads, non-articulated kneepads, and articulated kneepads). For each posture, peak and mean pressure on the anatomic landmarks of the knee were obtained. The majority of the pressure was found to be transmitted to the knee via the combined patellar tendon and tibial tubercle rather than through the patella. While the kneepads tested decreased the maximum pressure experienced at the combined patellar tendon and tibial tubercle, peak pressures of greater than 25 psi were still experienced over structures commonly injured in mining (e.g. bursa sac - bursitis/Miner’s Knee). The major conclusion of this study is that novel kneepad designs that redistribute the stresses at the knee across a greater surface area and to other regions of the leg away from key structures of the knee are needed.     

Task-specific postures in low-seam underground coal mining

The objective of this study was to determine low-seam mine worker exposure to various postures as they pertain to job classifications and job tasks. Sixty-four mine workers from four low-seam coal mines participated. The mine workers reported the tasks they were required to complete and the two postures they used most frequently to perform them. They were provided with a schematic of postures from which to select. The two postures reported most frequently were identified for each task along with the job classification of the workers performing the tasks. Of the 18 tasks reported, over two thirds were performed by at least two different job classifications and over one third were performed by four or more job classifications. Across tasks, the postures used appeared to vary greatly. However, when grouped by job classification, the most frequently reported posture across all job classifications was kneeling near full flexion. Operating the continuous miner was associated with frequent squatting and was likely used because it affords great mobility, allowing operators to move quickly to avoid hazards. However, for environments with a restricted vertical height such as low-seam mining, the authors recommend squatting be avoided as data demonstrates that large amounts of femoral rollback and high muscle activity for the extensors when performing lateral lifts in this posture. Kneeling near full flexion was reported as the most frequently used posture by all job classifications and was likely due to the fact that it requires the least amount of muscle activity to maintain and has reduced pressures at the knee. However, the authors recommend this posture be avoided when performing lateral lifting tasks. Like squatting, kneeling near full flexion results in increased femoral rollback and may increase the stresses applied to the meniscus. Unlike lateral lifting, maintaining a static posture results in knee loading and muscle activity such that the mine worker should consider kneeling near full flexion and sitting on their heels. Although kneeling near full flexion is associated with injuries, there are benefits to this posture that are realized when statically kneeling (minimal muscle activity, allows worker to maintain an upright torso in low heights, and decreased loading at the knee). However, cartilage is avascular and nourished by synovial fluid. Therefore, one should frequently rotate between postures, assuming a more upright kneeling posture when possible and frequently fully flexing and extending the knee allowing nutrients to the cartilage.Relevance to industryIn 2009, over one fourth of underground coal mines that produced coal in the United States were considered low seam with an average working height of <109.2 cm (MSHA, 2009) restricting workers to their knees. Data exists regarding the biomechanical implications of kneeling postures and demonstrates the possibility of detrimental consequences to varying degrees for each posture. With each posture posing a different level of exposure to musculoskeletal disorder risk factors, it is essential to determine the postures mine workers use to perform their job tasks and how their postural options are restricted by the low-seam underground mining environment.     

Electromyography of the thigh muscles during lifting tasks in kneeling and squatting postures

Underground coal miners who work in low-seam mines frequently handle materials in kneeling or squatting postures. To assess quadriceps and hamstring muscle demands in these postures, nine participants performed lateral load transfers in kneeling and squatting postures, during which electromyographic (EMG) data were collected. EMG activity was obtained at five points throughout the transfer for three quadriceps muscles and two hamstring muscles from each thigh. ANOVA results indicated that EMG data for nine of 10 thigh muscles were affected by an interaction between posture and angular position of the load lifted (p < 0.001). Muscles of the right thigh were most active during the lifting portion of the task (lifting a block from the participant's right) and activity decreased as the block was transferred to the left. Left thigh muscles showed the opposite pattern. EMG activity for the majority of thigh muscles was affected by the size of the base of support provided by different postures, with lower EMG activity observed with a larger base of support and increased activity in postures where base of support was reduced (p < 0.05). Thigh EMG activity was lowest in postures with fully flexed knees, which may explain worker preference for this posture. However, such postures are also associated with increased risk of meniscal damage. STATEMENT OF RELEVANCE: Kneeling and squatting postures are sometimes used for manual lifting activities, but are associated with increased knee injury risk. This paper examines the EMG responses of knee extensors/flexors to lifting in these postures, discusses the impact of posture and kneepads on muscle recruitment and explores the implications for work in such postures.     

Peak activation of lower limb musculature during high flexion kneeling and transitional movements

Few studies have measured lower limb muscle activation during high knee flexion or investigated the effects of occupational safety footwear. Therefore, our understanding of injury and disease mechanisms, such as knee osteoarthritis, is limited for these high-risk postures. Peak activation was assessed in eight bilateral lower limb muscles for twelve male participants, while shod or barefoot. Transitions between standing and kneeling had peak quadriceps and tibialis anterior (TA) activations above 50% MVC. Static kneeling and simulated tasks performed when kneeling had peak TA activity above 15% MVC but below 10% MVC for remaining muscles. In three cases, peak muscle activity was significantly higher (mean 8.9% MVC) when shod. However, net compressive knee joint forces may not be significantly increased when shod. EMG should be used as a modelling input when estimating joint contact forces for these postures, considering the activation levels in the hamstrings and quadriceps muscles during transitions.

Practitioner Summary: Kneeling transitional movements are used in activities of daily living and work but are linked to increased knee osteoarthritis risk. We found peak EMG activity of some lower limb muscles to be over 70% MVC during transitions and minimal influence of wearing safety footwear.     

Are knee savers and knee pads a viable intervention to reduce lower extremity musculoskeletal disorder risk in residential roofers?

One factor commonly associated with musculoskeletal disorder risk is extreme postures. To lessen this risk, extreme postures should be reduced using proactive and prevention-focused methods. The effect of combinations of two interventions, knee pads and knee savers, on lower extremity kinematics during deep or near full flexion kneeling on differently sloped surfaces was analyzed. Nine male subjects were requested to keep a typical resting posture while kneeling on a sloped roofing simulator with and without knee pads and knee savers. Three-dimensional peak knee kinematics were recording using a motion capture system. The kinematic data were analyzed with a two-way—4(intervention) X 3(slope)—repeated measure analysis of variance (ANOVA). It was observed that knee pads did not alter lower extremity kinematics in a way that may reduce musculoskeletal injury risk, but they do provide comfort. Knee savers did statistically significantly reduce peak lower extremity kinematics, however these changes were small and it is uncertain if the changes will reduce musculoskeletal injury risk. This study has provided initial data that supports the use of knee savers as a potential intervention to reduce musculoskeletal disorder risk due to lower extremity joint angles on a sloped surface, nonetheless, further testing involving other musculoskeletal disorder risk factors is needed prior to a conclusive recommendation.     

Traumatogenic factors affecting the knees of carpet installers

An ergonomics analysis of carpet installation tasks was performed. The purpose was to identify and quality potential sources of biomechanical trauma that may be responsible for the high rates of knee morbidity found by previous researchers among carpet layers. Nine carpet layers were studied either at an apartment building worksite or at a training school. Results from a job analysis indicated that workers spent approximatately 75% of their time in the kneeling position using a tool called a knee-kicker to stretch and install carpet. Awkward body postures were identified from films of workers installing carpets. At the moment of impact the knee is severely flexed, subtended angles were less than 60 degrees. To obtain measures of impact force on the knee, the kicker-tool was instrumented with a load cell. Workers who executed the hardest kicks with the tool produced impact peak forces that averaged 3019 newtons (N), which is equivalent to about four times body weight. Measures from an accelerometer attached to the worker's knee showed values in ecxess of 120 m/s², which are comparable to those found during vigorous running and jumping exercises. The results imply that repetitive impact of the knee joint from the use of the knee-kicker combined with knee flexion, kneeling and squatting may be responsible for the high level of occupational knee-morbidity found among carpet layers.     

The effects of a simulated occupational kneeling exposure on squat mechanics and knee joint load during gait

Occupational kneeling is associated with an increased risk for tibiofemoral knee osteoarthritis. Forces on the knee in the kneeling posture, as well as the greater incidence of meniscus tears among workers, likely contribute to the increased risk. We hypothesise that an additional mechanism may contribute – altered neuromuscular control due to prolonged high knee flexion. Forty participants (20 male, 20 female) completed an evaluation of gait and squatting before, immediately following, and 30 min following a 30 min simulated occupational kneeling exposure. An increase in the peak external knee adduction moment and a delay in vastus medialis activation onset during walking were observed post-kneeling, as well as increased frontal plane knee motion during squatting. This was the first investigation to find changes in high flexion transitions as a result of kneeling. Greater frontal plane knee motion may increase the risk for meniscal tears, and subsequently, knee osteoarthritis.

Practitioner Summary: A 30 min simulated occupational kneeling exposure resulted in small but significant gait changes. The greatest effect was on frontal plane knee movement during squatting, which is especially relevant to occupations requiring frequent kneeling/squatting. This increased motion may indicate an increased risk of injury, which supports a link to knee osteoarthritis.     

Data mining using clinical physiology at discharge to predict ICU readmissions

Patient readmissions to intensive care units (ICUs) are associated with increased mortality, morbidity and costs. Current models for predicting ICU readmissions have moderate predictive value, and can utilize up to twelve variables that may be assessed at various points of the ICU inpatient stay. We postulate that greater predictive value can be achieved with fewer physiological variables, some of which can be assessed in the 24 h before discharge. A data mining approach combining fuzzy modeling with tree search feature selection was applied to a large retrospectively collected ICU database (MIMIC II), representing data from four different ICUs at Beth Israel Deaconess Medical Center, Boston. The goal was to predict ICU readmission between 24 and 72 h after ICU discharge. Fuzzy modeling combined with sequential forward selection was able to predict readmissions with an area under the receiver-operating curve (AUC) of 0.72 ± 0.04, a sensitivity of 0.68 ± 0.02 and a specificity of 0.73 ± 0.03. Variables selected as having the highest predictive power include mean heart rate, mean temperature, mean platelets, mean non-invasive arterial blood pressure (mean), mean spO2, and mean lactic acid, during the last 24 h before discharge. Collection of the six predictive variables selected is not complex in modern ICUs, and their assessment may help support the development of clinical management plans that potentially mitigate the risk of readmission.     

Effects of posture on dynamic back loading during a cable lifting task

This study evaluated spinal loads associated with lifting and hanging heavy mining cable in a variety of postures. This electrical cable can weigh up to 10 kg per metre and is often lifted in restricted spaces in underground coal mines. Seven male subjects performed eight cable lifting and hanging tasks, while trunk kinematic data and trunk muscle electromyograms (EMGs) were obtained. The eight tasks were combinations of four postures (standing, stooping, kneeling on one knee, or kneeling on both knees) and two levels of cable load (0 N or 100 N load added to the existing cable weight). An EMG-assisted model was used to calculate forces and moments acting on the lumbar spine. A two-way split-plot ANOVA showed that increased load (p < 0.05) and changes in lifting posture (p < 0.05) independently affected trunk muscle recruitment and spinal loading. The increase in cable load resulted in higher EMG activity of all trunk muscles and increased axial and lateral bending moments on the spine (p < 0.05). Changes in posture caused more selective adjustments in muscle recruitment and affected the sagittal plane moment (p < 0.05). Despite the more selective nature of trunk EMG changes due to posture, the magnitude of changes in spinal loading was often quite dramatic. However, average compression values exceeded 3400 N for all cable lifting tasks.     

Effects of posture on dynamic back loading during a cable lifting task

This study evaluated spinal loads associated with lifting and hanging heavy mining cable in a variety of postures. This electrical cable can weigh up to 10 kg per metre and is often lifted in restricted spaces in underground coal mines. Seven male subjects performed eight cable lifting and hanging tasks, while trunk kinematic data and trunk muscle electromyograms (EMGs) were obtained. The eight tasks were combinations of four postures (standing, stooping, kneeling on one knee, or kneeling on both knees) and two levels of cable load (0 N or 100 N load added to the existing cable weight). An EMG-assisted model was used to calculate forces and moments acting on the lumbar spine. A two-way split-plot ANOVA showed that increased load (p<0.05) and changes in lifting posture (p<0.05) independently affected trunk muscle recruitment and spinal loading. The increase in cable load resulted in higher EMG activity of all trunk muscles and increased axial and lateral bending moments on the spine (p<0.05). Changes in posture caused more selective adjustments in muscle recruitment and affected the sagittal plane moment (p<0.05). Despite the more selective nature of trunk EMG changes due to posture, the magnitude of changes in spinal loading was often quite dramatic. However, average compression values exceeded 3400 N for all cable lifting tasks.     

Where Does the Mouse Go? An Investigation into the Placement of a Body-Attached TouchPad Mouse for Wearable Computers

We investigated the effects of placement of a TouchPad input device on a user's body for the control of a wearable computer. This study involved 25 subjects performing selection tasks with a TouchPad mouse while wearing a wearable computer on their back and using a head-mounted display. Each subject performed the tasks in 27 different combinations of four postures (sitting, kneeling, standing and prone) and seven different placements of the TouchPad mouse on the subject's body (forearm, thigh by 2, torso by 2, and upper arm by 2). We measured the time and error rate to complete the selection of a circular target. The results for the effects due to posture showed that there were similar time effects for sitting, standing and kneeling. When examining the effects resulting from mouse position, the front of the thigh was shown to be the best position of the mouse. When the posturing and mouse position conditions were combined, the results indicated that the thigh front mouse position would be most appropriate for sitting, kneeling and standing postures, and the forearm mouse position would be best for the prone position.     

Study on the variation of peak isometric strength and EMG activity in static field-simulated lifting postures

Peak isometric strength was measured from 10 adult Indian construction workers in eight different field-simulated (FS) postures. This peak-strength data in these FS postures were compared with symmetric postures. In symmetric postures, the vertical load positions were kept the same as FS postures and the points of force exertion were fixed at 40 cm distance in front of the subject. From both symmetric and FS static strength data, it was shown that the maximum peak strength occurred at medium vertical height level and decreased with both increase and decrease of the vertical height level. The maximum and minimum peak strengths were obtained in different FS postures as 222.85±61.15 N and 85.65±19.89 N, respectively. It was observed that the lifted weight in the field was 12.0 kg, which corresponds to 54.54% and 137.3% (i.e. >100%) of these maximum and minimum peak-strength values. This result indicated the prevalence of high risk factors in the field. During this study, surface EMGs from four different muscles (i.e. trapezius, external oblique, rectus abdominis and erector spinae) were collected while exerting the peak isometric strength. From ANOVA analysis, it was shown that the erector spinae and trapezius activities were significantly (p⩽0.05) related to the peak-strength value, whereas external oblique and rectus abdominis activities were not. It was also observed that RMS of erector spinae activity increases with ipsi-lateral increase of asymmetry angle along with the decrease in maximum static peak-strength level in FS postures.Relevance to industryThe peak static strength and EMG activities were measured in FS postures to highlight the potential risk factors in building construction industry. This study was conducted on adult female building construction workers, where the female construction workers were not well represented in the literature. Moreover, from this study, it is very clear that the actual field postures are of more complex in nature than the simulation studies, as mentioned in earlier studies.     

Modeling of the condyle elements within a biomechanical knee model

The development of a computational multibody knee model able to capture some of the fundamental properties of the human knee articulation is presented. This desideratum is reached by including the kinetics of the real knee articulation. The research question is whether an accurate modeling of the condyle contact in the knee will lead to reproduction of the complex combination of flexion/extension, abduction/adduction, and tibial rotation observed in the real knee. The model is composed by two anatomic segments, the tibia and the femur, whose characteristics are functions of the geometric and anatomic properties of the real bones. The biomechanical model characterization is developed under the framework of multibody systems methodologies using Cartesian coordinates. The type of approach used in the proposed knee model is the joint surface contact conditions between ellipsoids, representing the two femoral condyles, and points, representing the tibial plateau and the menisci. These elements are closely fitted to the actual knee geometry. This task is undertaken by considering a parameter optimization process to replicate experimental data published in the literature, namely that by Lafortune and his coworkers in 1992. Then kinematic data in the form of flexion/extension patterns are imposed on the model corresponding to the stance phase of the human gait. From the results obtained, by performing several computational simulations, it can be observed that the knee model approximates the average secondary motion patterns observed in the literature. Because the literature reports considerable inter-individual differences in the secondary motion patterns, the knee model presented here is also used to check whether it is possible to reproduce the observed differences with reasonable variations of bone shape parameters. This task is accomplished by a parameter study, in which the main variables that define the geometry of condyles are taken into account. It was observed that the data reveal a difference in secondary kinematics of the knee in flexion versus extension. The likely explanation for this fact is the elastic component of the secondary motions created by the combination of joint forces and soft tissue deformations. The proposed knee model is, therefore, used to investigate whether this observed behavior can be explained by reasonable elastic deformations of the points representing the menisci in the model.     

Passive single chip wireless microwave pressure sensor

A novel micromachined passive wireless pressure sensor is presented. The device consists of a tuned circuit operating at 10 GHz fabricated on to a SiO₂ membrane, supported on a silicon wafer. A pressure difference across the membrane causes it to deflect so that an antenna circuit detunes. The circuit is remotely interrogated to read off the sensor data wirelessly. The chip area is 5 mm × 4 mm and the membrane area is 2 mm² with a thickness of 4 μm. Two on-chip passive resonant circuits were investigated: a meandered dipole and a zigzag antenna. Both have a physical length of 4.25 mm. The sensors show a shift in their resonant frequency in response to changing pressure of 10.28–10.27 GHz for the meandered dipole, and 9.61–9.58 GHz for the zigzag antenna. The sensitivities of the meandered dipole and zigzag sensors are 12.5 kHz/mbar and 16 kHz/mbar respectively.     

Piezoresistive TiB2/silicone rubber composites for circuit breakers

Piezoresistive composites with high hardness and conductivity are required for circuit breakers for multi-cycle operation under large current flow. Based on the simulation results for the mechanical behavior of piezoresistive composites, we developed piezoresistive composites with conductive TiB₂ ceramic materials and silicone rubber. TiB₂ up to 70 vol.% was embedded into the polymer matrix without any mechanical deterioration while the electrical resistance was decreased with increasing TiB₂ content. Piezoresistive composites with 70 vol.% TiB₂ particles exhibited a resistance of 1.7 Ω at a pressure of 1.1 MPa. A circuit breaker with the fabricated piezoresistive composites acted as a switch with a response time of around 2 ms.     

Critical pressure for capillary valves in a Lab-on-a-Disk: CFD and flow visualization

Capillary valves are used as pressure barriers to control flow sequencing in microfluidic devices. Influence of valves height on liquid flow pattern and critical pressure are studied through flow visualization and CFD predictions (Gambit® 2.2.30 and FLUENT® 6.2.16). Both hydrophilic and hydrophobic walls are studied. Results show that the surface tension plays a major role in the liquid progress through the microchannel/valve and also in the valve filling process. Critical pressure varies linearly with the valve hydraulic diameter in the range 0.91 < D_h < 3.5 [mm] according to: P = 14.14 · D_h + 47.42 [Pa].     

Postural, epidemiological and biomechanical analysis of luggage handling in an aircraft luggage compartment

Loading and unloading of luggage in an aircraft luggage compartment is carried out manually in uncomfortable working position. In this study, the loading work was analysed by surveying musculoskeletal symptoms, by recording the working postures and techniques at work, and by simulating the loading work in a mock-up of a DC-9 aircraft compartment. Low back, knees and shoulders were exposed to mechanical load in luggage handling. Video recordings were used to analyse posture and work technique. In the simulated luggage compartment in the laboratory, ground reaction forces, intra-abdominal pressure (IAP) and electromyography (EMG) signals from back and shoulder muscles were recorded simultaneously. Loading in sitting, squatting and kneeling were the postures that were used the most often. Unloading was generally less stressful than loading, involving less static work. Handling time was shortest when kneeling but knee symptoms were dominant. Lateral ground reaction forces and EMG activity from trapezius were highest when sitting, and IAP peaks were greatest when squatting. Thus each posture had major, though differing, disadvantages and a radical redesign of the DC-9 luggage compartment was clearly indicated.     

Development of an automation system to evaluate the three-dimensional oxygen distribution in wastewater biofilms using microsensors

In this paper the authors describe the development of an automation system applicable to environmental biofilm studies. The automation system controls a combined oxygen microsensor to measure the three-dimensional dissolved oxygen distribution in a wastewater biofilm sample. The biofilm is sampled from a rotating biological contactor in a municipal wastewater treatment plant. The automation system consists of a data acquisition system, a motion control system, and a computer program. The combined oxygen microsensor consists of a sensing electrode, a reference electrode, a guard cathode, an oxygen permeable membrane, and an electrolyte solution. The automation system allows the acquisition and storage of data from 4000 measurements from the microsensor and the precise positioning of the microsensor in order to measure 100 dissolved oxygen profiles in a 1000 μm × 1000 μm biofilm area. The three-dimensional profile shows that the dissolved oxygen concentration in the biofilm sample is highly heterogeneous and it revealed “pockets” of dissolved oxygen in deep sections of the biofilm sample. The automation system and the combined oxygen microsensor were proven to be tools that improve the quantity and quality of experimental results needed to understand important functions in biofilms used in wastewater treatment.     

Experimental study and thermodynamic modelling of the B-Fe-Mn ternary system

This work is focused on an experimental study of phase equilibria in the B-Fe-Mn ternary system combined with a CALPHAD theoretical analysis with the aim of creating a reliable theoretical thermodynamic dataset for calculation of the phase diagram of the ternary system. Boron is modelled as an interstitial element in all solid solutions of Fe and Mn. In the experimental study, B-Mn-Fe alloys were prepared and heat-treated at 873 K for 90 days/2160 h and at 1223 K for 60 days/1440 h. Following heat treatment, the phase equilibria and composition of the coexisting phases were determined using scanning electron microscopy and X-ray diffraction analysis. The experimental results obtained, together with experimental results collected from the literature, were used in the optimization of the thermodynamic parameters by using the CALPHAD method. The result of this work is an optimized thermodynamic dataset for the B-Fe-Mn ternary system allowing the phase diagram and thermodynamic properties to be calculated.     

Thermodynamic study of the cerium–cadmium system

Cadmium vapor pressures were determined over Ce–Cd samples by an isopiestic method. The measurements were carried out in the temperature range from 690 to 1080 K and over a composition range of 48–85 at% Cd. From the vapor pressures thermodynamic activities of Cd were derived for all samples at their respective sample temperatures, and partial molar enthalpies of Cd were obtained from the temperature dependence of the activities. With these partial molar enthalpies the Cd activities were converted to a common temperature of 823 K. By means of a Gibbs–Duhem integration Ce activities were calculated, using a corresponding literature value for the two-phase field (CeCd₁₁+L) as integration constant. Finally integral Gibbs energies were calculated for the composition range 48–100 at% Cd with a minimum value of −37 kJ g-atom⁻¹ at 823 K in the phase CeCd. Phase boundaries of the intermetallic compounds CeCd, CeCd₂, Ce₁₃Cd₅₈, and CeCd₁₁ were estimated from the vapor pressure measurements and from SEM analyses.