Development and validation of a behavioural video coding scheme for detecting mental workload in manual assembly.

Manual assembly in the future Industry 4.0 workplace will put high demands on operators' cognitive processing. The development of mental workload (MWL) measures therefore looms large. Physiological gauges such as electroencephalography (EEG) show promising possibilities, but still lack sufficient reliability when applied in the field. This study presents an alternative measure with a substantial ecological validity. First, we developed a behavioural video coding scheme identifying 11 assembly behaviours potentially revealing MWL being too high. Subsequently, we explored its validity by analysing videos of 24 participants performing a high and a low complexity assembly. Results showed that five of the behaviours identified, such as freezing and the amount of part rotations, significantly differed in occurrence and/or duration between the two conditions. The study hereby proposes a novel and naturalistic method that could help practitioners to map and redesign critical assembly phases, and researchers to enrich validation of MWL-measures through measurement triangulation. Practitioner summary: Current physiological mental workload (MWL) measures still lack sufficient reliability when applied in the field. Therefore, we identified several observable assembly behaviours that could reveal MWL being too high. The results propose a method to map MWL by observing specific assembly behaviours such as freezing and rotating parts. Abbreviations: MWL: mental workload; EEG: electroencephalography; fNIRS: functional near infrared spectroscopy; AOI: area of interest; SMI: SensoMotoric Instruments, ETG: Eye-Tracking Glasses; FPS: frames per second; BORIS: Behavioral Observation Research Interactive Software; IRR: inter-rater reliability; SWAT: Subjective Workload Assessment Technique; NASA-TLX: National Aeronautics and Space Administration Task Load Index; EL: emotional load; DSSQ: Dundee Stress State Questionnaire; PHL: physical load; SBO: Strategisch Basis Onderzoek.

Differential Interaction of the Staphylococcal Toxins Panton-Valentine Leukocidin and γ-Hemolysin CB with Human C5a Receptors.

Staphylococcus aureus is well adapted to the human host. Evasion of the host phagocyte response is critical for successful infection. The staphylococcal bicomponent pore-forming toxins Panton-Valentine leukocidin LukSF-PV (PVL) and γ-hemolysin CB (HlgCB) target human phagocytes through interaction with the complement receptors C5aR1 and C5aR2. Currently, the apparent redundancy of both toxins cannot be adequately addressed in experimental models of infection because mice are resistant to PVL and HlgCB. The molecular basis for species specificity of the two toxins in animal models is not completely understood. We show that PVL and HlgCB feature distinct activity toward neutrophils of different mammalian species, where activity of PVL is found to be restricted to fewer species than that of HlgCB. Overexpression of various mammalian C5a receptors in HEK cells confirms that cytotoxicity toward neutrophils is driven by species-specific interactions of the toxins with C5aR1. By taking advantage of the species-specific engagement of the toxins with their receptors, we demonstrate that PVL and HlgCB differentially interact with human C5aR1 and C5aR2. In addition, binding studies illustrate that different parts of the receptor are involved in the initial binding of the toxin and the subsequent formation of lytic pores. These findings allow a better understanding of the molecular mechanism of pore formation. Finally, we show that the toxicity of PVL, but not of HlgCB, is neutralized by various C5aR1 antagonists. This study offers directions for the development of improved preclinical models for infection, as well as for the design of drugs antagonizing leukocidin toxicity.

When local phytotherapies meet biomedicine. Cross-sectional study of knowledge and intercultural practices against malaria in Eastern French Guiana.

ETHNOPHARMACOLOGICAL RELEVANCE: In French Guiana, traditional phytotherapies are an important part of self-healthcare, however, a precise understanding of the interactions between local phytotherapies and biomedicine is lacking. Malaria is still endemic in the transition area between French Guiana and Brazil, and practices of self-treatment, although difficult to detect, have possible consequences on the outcome of public health policies. AIM OF THE STUDY: The objectives of this research were 1) to document occurences of co-medication (interactions between biomedicine and local phytotherapies) against malaria around Saint-Georges de l'Oyapock (SGO), 2) to quantify and to qualify plant uses against malaria, 3) and to discuss potential effects of such co-medications, in order to improve synergy between community efforts and public health programs in SGO particularly, and in Amazonia more broadly. MATERIALS AND METHODS: This cross-sectional study was conducted in 2017 in SGO. Inhabitants of any age and nationality were interviewed using a questionnaire (122 questions) about their knowledge and habits regarding malaria, and their use of plants to prevent and treat it. They were invited to show their potential responses on a poster illustrating the most common antimalarial plants used in the area. In order to correlate plant uses and malaria epidemiology, all participants subsequently received a medical examination, and malaria detection was performed by Rapid Diagnostic Test (RDT) and Polymerase Chain Reaction (PCR). RESULTS: A total of 1566 inhabitants were included in the study. Forty-six percent of them declared that they had been infected by malaria at least once, and this rate increased with age. Every person who reported that they had had malaria also indicated that they had taken antimalarial drugs (at least for the last episode), and self-medication against malaria with pharmaceuticals was reported in 142 cases. A total of 550 plant users was recorded (35.1% of the interviewed population). Among them 95.5% associated pharmaceuticals to plants. All plants reported to treat malaria were shared by every cultural group around SGO, but three plants were primarily used by the Palikur: Cymbopogon citratus, Citrus aurantifolia and Siparuna guianensis. Two plants stand out among those used by Creoles: Eryngium foetidum and Quassia amara, although the latter is used by all groups and is by far the most cited plant by every cultural group. Cultivated species accounts for 91.3% of the use reports, while wild taxa account for only 18.4%. CONCLUSIONS: This study showed that residents of SGO in French Guiana are relying on both traditional phytotherapies and pharmaceutical drugs to treat malaria. This medical pluralism is to be understood as a form of pragmatism: people are collecting or cultivating plants for medicinal purposes, which is probably more congruent with their respective cultures and highlights the wish for a certain independence of the care process. A better consideration of these practices is thus necessary to improve public health response to malaria.

Activation of endogenous thrombin receptors causes clustering and sensitization of epidermal growth factor receptors of swiss 3T3 cells without transactivation.

The G protein-coupled thrombin receptor can induce cellular responses in some systems by transactivating the epidermal growth factor (EGF) receptor. This is in part due to the stimulation of ectoproteases that generate EGF receptor ligands. We show here that this cannot account for the stimulation of proliferation or migration by thrombin of Swiss 3T3 cells. Thrombin has no direct effect on the activation state of the EGF receptor or of its downstream effectors. However, thrombin induces the subcellular clustering of the EGF receptor at filamentous actin-containing structures at the leading edge and actin arcs of migrating cells in association with other signaling molecules, including Shc and phospholipase Cgamma1. In these thrombin-primed cells, the subsequent migratory response to EGF is potentiated. Thrombin did not potentiate the EGF-stimulated EGF receptor phosphorylation. Thus, in Swiss 3T3 cells the G protein-coupled thrombin receptor can potentiate the EGF tyrosine kinase receptor response when activated by EGF, and this appears to be due to the subcellular concentration of the receptor with downstream effectors and not to the overall ability of EGF to induce receptor transphosphorylation. Thus, the EGF receptor subcellular localization which is altered by thrombin appears to be an important determinant of the efficacy of downstream EGF receptor signaling in cell migration.

Asymptomatic Plasmodium falciparum and vivax infection in the neighborhood of Blondin, Saint-Georges-de-l'Oyapock District, French Guiana.

Optimized elimination strategies are needed to control transmission of malaria. As part of an elimination campaign, active detection of asymptomatic Plasmodium carriers by highly sensitive methods is deemed necessary. Asymptomatic carriage leads to complex scientific, ethical, and operational issues regarding individual or collective detection and treatment. To address this issue, a crosssectional study was carried out in French Guiana to determine the prevalence of asymptomatic Plasmodium carriage during an inter-epidemic season in the whole population of a neighborhood of Saint-Georges-de-l'Oyapock, along the Brazilian border. Fifty-eight participants out of 63 residents were screened. The median age was 23.3 years (range: 2 months-72 years), with a male/female sex-ratio of 0.56. The majority of the participants (74%, N = 43/58) reported a history of malaria, 12% (N = 7/58) during the past 12 months. All rapid diagnostic tests for malaria were negative. Among the 58 participants, malaria prevalence detected by nested-PCR (Polymerase Chain Reaction) was 3.6% (N = 2/56). Two asymptomatic carriers of Plasmodium were identified: one child with Plasmodium vivax and one adult with Plasmodium falciparum. These two carriers were treated and did not develop malaria within the eight months following the diagnosis. This study confirmed the presence of asymptomatic parasitaemias outside hyperendemic areas. However, the benefits of such an active detection and patient treatment to eliminate malaria in French Guiana need to be evaluated at a larger scale.

Bone mass and comparative rates of bone resorption and formation of fibular autografts: comparison of vascular and nonvascular grafts in dogs.

The metabolic fate of whole grafts that were either vascularized or nonvascularized were compared. This study was designed to quantify and correlate changes in bone resorption, formation, and mass in orthotopic, stably fixed, weight-bearing autografts. The grafts were 8-cm segments of the fibula that were internally fixed. Fibula segments subjected to sham operations, nonvascularized autografts, and vascularized autografts were studied in 16 dogs at three months after surgery. Three months prior to surgery the dogs were labeled repeatedly over two months with 3H-tetracycline and 3H-proline. Metabolic turnover of whole grafts was evaluated by quantifying loss of 3H-tetracycline for measuring postoperative resorption of bone mineral and loss of 3H-collagen for resorption of bone collagen. Net changes in bone dry weight, calcium, and collagen per whole grafts were obtained to determine differential changes in the mineral and matrix mass. The difference in change between bone resorption and bone mass was used to determine the amount of new bone formation that had replaced the resorbed bone. Vascularized autografts lost more mass (12%), and had more bone resorption (40%) and more bone formation (28%) than sham operated and unoperated fibulas. Nonvascularized grafts lost much more bone mass (48%) because resorption was large (61%) and formation was relatively small (13%). More new bone was formed in vascularized autografts than in nonvascularized autografts. During the incorporation of bone grafts, resorption is an early and rapid process, whereas formation is a late and slow process.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of mechanical testing device variables on polymer composite femoral stem strains.

Polymer composite femoral stems do not have a well-established in vitro mechanical testing method. The objective of this study was to examine mechanical testing devices for pressfit composite stems, using finite element analysis. The goals were to examine the effects of testing device design variables (geometry, material, interface friction, embedding height and applied load angle) and to reproduce the maximum strains of the stem implanted in a femur. The stem strains were affected by design changes to the testing device. The maximum normal and interlaminar shear strains of the composite stem in the femur were not as well reproduced by the testing device as were the maximum in-plane tensile strains. Decreasing the embedding height increased the stem strains and shifted the stem failure location from the neck to the embedding height. Testing a femoral stem using a testing device with a low embedding height may be inappropriate when trying to induce neck failure, since failure may occur at the embedding height instead of in the neck. A single-material testing device of birchwood, an orthotropic material with a longitudinal stiffness in the range of bone; best simulated a femur in this study.

Reduction of patellofemoral contact forces following anterior displacement of the tibial tubercle.

Retropatellar pain often accompanies malalignment syndromes and frequently is attributed to excessive patellofemoral contact stresses. Elevation (anterior displacement) of the tibial tubercle has been recommended to relieve these conditions. The degree to which patellar contact forces are decreased and the extent to which elevation alters medial-lateral forces have not been studied directly. We performed anterior translation of the tibial tubercle in knees from cadavers and measured the effect on the magnitude of the three-dimensional patellofemoral contact force with use of a specially designed 6-degrees-of-freedom force transducer, with the natural patellar articular surface in place. Measurements were made in nine knees (average age 67 years, range 46-92 years). The resultant contact force decreased linearly with increasing tubercle elevations of as much as 2.5 cm. The average reduction per centimeter of elevation was 17% of the force measured with no elevation. Elevation of the tubercle had an inconsistent effect on the medial-lateral component of the contact force. As the elevation was increased, six knees exhibited an increase in the medial-lateral component of the contact force acting medially on the knee and three knees exhibited a decrease in this force component. The results of this study show that, while elevation of the tubercle without medialization reduced the total contact force on the patella, the medial-lateral component of this force was altered in an unpredictable way.

Induction of bone by a demineralized bone matrix gel: a study in a rat femoral defect model.

Demineralized bone matrix contains osteoinductive factors and stimulates filling of gaps and defects with bone; however, it is difficult to handle by itself and various preparations have been tested. Demineralized bone matrix with a gel consistency now is available for clinical use. We studied, in a femoral segment defect in the rat, the effects of rat demineralized bone matrix gel with and without a ceramic substratum. This preparation is analogous to the human demineralized bone matrix in the same carrier, used clinically for humans. One hundred adult male Fischer rats were divided into 10 experimental groups. Independent variables included the presence or absence of hydroxyapatite ceramic cylinders, the presence of demineralized bone matrix in carrier or carrier alone (glycerol), and the duration of observation (1, 2, and 4 months). Defects filled with the gel alone had significantly higher radiographic scores for host-graft union at 4 months compared with ceramic with the gel, ceramic alone, or carrier alone. Demineralized bone matrix gel significantly increased the total histologic score for host-graft union, whether ceramic was present or not, and a three-way interaction occurred among ceramic, the gel, and time. Demineralized bone matrix gel was an effective inducer of bone formation in this model. An additional substratum was not required; in fact, significantly more bone was formed in the absence of the ceramic cylinder. Neither the gel nor the ceramic were impediments to revascularization of the defect. Host-graft union was enhanced by demineralized bone matrix gel but not by the ceramic cylinder.

Torsional loads in the early postoperative period following total hip replacement.

Torques generated in one subject during the early postoperative period were measured with a telemeterized total hip component. The patient was examined during gait, stair ascent, rising from a chair, and single-limb stance. The torques were plotted against both the resultant joint contact force and the force component directed along the stem axis. During gait, the maximum torque was 35 Nm, recorded at a walking velocity of 1.7 m/sec. The peak torques during stair ascent and during rising from a seated position were found to be 23 and 15 Nm, respectively. The maximum value for torque measured in this study was 37 Nm during one attempt at single-limb stance. Comparison of plots for torque versus stem-axis component for the four activities shows that the torque increased more rapidly for chair exits than for gait up to resultant contact force values of as much as 1,000 N. For stair ascent, the same was true to values of 1,400 N. Within any given activity, the relationship between stem torque and resultant or stem-axis force showed considerable variability. These results indicate that experiments evaluating the stability of femoral components in total hip arthroplasty should incorporate a component directed along the stem axis, as well as a component normal to the plane of the prosthesis. The results also suggest that theoretical stress analysis models should consider the broad variability in the orientation of the joint force at the hip.

Telemeterized in vivo hip joint force data: a report on two patients after total hip surgery.

Two telemeterized femoral components were implanted in two patients as part of normal total hip replacement procedures. The two components were instrumented to measure the three force components directed along: (a) the neck axis, (b) transverse to the neck axis and in the plane of the prosthesis, and (c) transverse to the neck axis and perpendicular to the plane of the prosthesis. Data were collected at multiple sessions during the early postoperative period for a number of standard activities, including gait, stair climbing, rising from a chair, single leg stance, double leg stance, ipsilateral and contralateral straight leg lifts while supine, ipsilateral flexion and extension while standing, and ipsilateral abduction while standing and lying on the contralateral side. These data are summarized and compared with the published results from analytic studies and with the results from previous studies using instrumented femoral components. Peak loads for gait during the period of study were roughly 2.7 body weights (BW) when the patients walked at their normal pace. Contact forces at the hip during stationary single leg stance approximated the peak loads during gait with values ranging from 2.1 to 2.8 BW. The highest forces recorded reached values approaching 5.5 BW and occurred during periods of instability while the patient engaged in stationary single leg stance. Our in vivo data indicate that forces generated during the above activities increase in magnitude quite rapidly during the early postoperative period and that during this period the patients have the ability to perform the activities of daily living without generating the high amplitude joint contact forces suggested by the results of dynamic studies. Joint contact forces during gait were found to depend on speed, but the high absolute magnitudes predicted by model studies were not supported by the in vivo data.

Determination of stress patterns in root-filled teeth incorporating various dowel designs.

A theoretical investigation has utilized the finite element technique to analyze mechanical stress patterns in a reconstructed maxillary central incisor. A series of designs for endodontic dowel posts incorporated into prosthesis has been comparatively evaluated. For the load condition considered, the results show that minor changes in the stress patterns are produced by the post diameter, length, and taper variations considered. 1. In general, larger post diameters decrease the maximum stresses for both the cylindrical and tapered designs. Variation of diameters over a 15% range produced stress variations of about 8%. 2. The effect of post length on the highest stresses in bending was less than the diameter changes. The real effect of the length changes was to change the location of the stress concentrations that occurred at the post apex in all cases. 3. The effect of taper was found to be slight if the local tapered-post diameter was comparable to the cylindrical post diameter in the high-stress region. 4. For the load considered in this study, the tapered-post design experienced slightly higher tensile and slightly lower shear stresses than the cylindrical post. 5. Using the peak stresses in the dentin and at the dentin-post interface as a criterion, the cylindrical post with the largest diameter is the best design among those examined.

The effect of osteogenin (a bone morphogenetic protein) on the formation of bone in orthotopic segmental defects in rats.

We studied the effects of partially purified, natural osteogenin, a bone morphogenetic protein, on the formation of bone in rats. An osteoperiosteal segmental defect, eight millimeters wide, in the middle of the femoral diaphysis was created bilaterally in thirty-six adult male Fischer rats and stabilized with a polyacetyl plate and threaded Kirschner wires. One defect was filled with a cylinder of 60 per cent hydroxyapatite and 40 per cent tricalcium phosphate ceramic (pore diameter, 250 to 400 micrometers) containing 100 micrograms of partially purified bovine osteogenin, and the contralateral defect was filled with a hydroxyapatite-tricalcium ceramic cylinder without osteogenin. Eighteen animals (six animals each at one, two, and four months after the operation) were studied histologically and histomorphometrically. The implants from eighteen additional animals (six animals each at one, two, and four months after the operation) were subjected to biomechanical testing. Histomorphometry revealed that the total area of bone, the area of bone outside of the implant, and the amount of bone within the pores of the implant were all significantly (p < or = 0.05) greater in the femora that had an implant with osteogenin than in those that had an implant without osteogenin at most time-periods. The presence of osteogenin had no significant effect on the biomechanical parameters measured in this study.

The influence of surface-blasting on the incorporation of titanium-alloy implants in a rabbit intramedullary model.

The apposition of new bone to polished solid implants and to implants with surfaces that had been blasted with one of three methods of grit-blasting was studied in a rabbit intramedullary model to test the hypothesis that blasted implant surfaces support osseous integration. Intramedullary titanium-alloy (Ti-6Al-4V) plugs, press-fit into the distal aspect of the femoral canal, were implanted bilaterally in fifty-six rabbits. Four surface treatments were studied: polished (a surface roughness of 0.4 to 0.6 micrometer) and blasted with stainless-steel shot (a surface roughness of five to seven micrometers), with thirty-six-grit aluminum oxide (a surface roughness of five to seven micrometers), or with sixty-grit aluminum oxide (a surface roughness of three to five micrometers). Localized attachment of new bone to the surfaces of the blasted implants was present radiographically at twelve weeks. The total bone area was significantly affected by the level of the section (the diaphysis had a greater bone area than the proximal part of the metaphysis and the proximal part of the metaphysis had a greater bone area than the distal part of the metaphysis; p < 0.001) and the quadrant within each section (the posterior and anterior quadrants had greater bone area than the medial and lateral quadrants; p < 0.00001). The length of the bone-implant interface was significantly affected by the surface treatment (the length of the bone-implant interface for the implants that had been blasted with sixty-grit aluminum oxide was greater than the length for the polished implants; p = 0.02), the time after implantation (the interface was longer at six and twelve weeks than at three weeks; p < 0.00001), and the level of the section (the interface was longer at the diaphysis than at the proximal part of the metaphysis and longer at the proximal part of the metaphysis than at the distal part of the metaphysis; p = 0.004). Blasting of the surface of titanium-alloy implants did not have an effect on the area of bone formation around the implants, but it did significantly affect the area of bone formation on the implant and the shear strength at the bone-implant interface. The two effects were not necessarily parallel, as significantly less (p < 0.05) bone formed on implants that had been blasted with stainless-steel shot than on those blasted with aluminum grit, whereas their interface shear strengths were similar.

Biological and physical properties of autogenous vascularized fibular grafts in dogs.

The biological and biomechanical properties of normal fibulae, fibulae that had had a sham operation, and both vascularized and non-vascularized autogenous grafts were studied in dogs at three months after the operation. The study was designed to quantify and correlate changes in these properties in orthotopic, stably fixed, weight-bearing grafts and to provide a baseline for additional studies of allografts. The grafts were eight centimeters long and internally fixed. The mechanical properties of the grafts were studied by torsional testing. Metabolic turnover of the grafts was evaluated by preoperative labeling of the dogs with 3H-tetracycline for resorption of bone mineral and with 3H-proline for turnover of collagen. Cortical bone area and porosity were measured. Postoperative formation of bone was evaluated by sequential labeling with fluorochrome. The vascularized grafts resembled the fibulae that had had a sham operation and those that had not had an operation with regard to the total number of osteons and the remodeling process, as measured both morphometrically and metabolically. The vascularized grafts were stronger and stiffer than the non-vascularized grafts and were not different from the bones that had had a sham operation. In contrast, the non-vascularized grafts were smaller, weaker, less stiff, and more porotic, had fewer osteons, and demonstrated increased turnover and resorption compared with the vascularized grafts, the bones that had had a sham operation, and the bones that had not been operated on.

Critical biological determinants of incorporation of non-vascularized cortical bone grafts. Quantification of a complex process and structure.

Our goal in this study was to evaluate the effects of and the interaction between the hypothesized principal determinants of the incorporation of grafts: antigenicity and treatment of the graft. We implanted fresh and frozen cortical bone grafts that were matched for both major and non-major histocompatibility complex antigens (syngeneic grafts), matched for major but not for non-major histocompatibility complex antigens (minor mismatch), and mismatched for both major and non-major histocompatibility complex antigens (major mismatch). We used a rat model with an eight-millimeter segmental defect in the femur. The construct was stabilized with a plastic plate, threaded Kirschner wires, and cerclage wires. We evaluated the grafts at one, two, and four months after implantation. We measured the immune response; assessed the incorporation of the graft with use of histological examination, biomechanical testing, and quantitative isotopic kinetics; and statistically analyzed the effects of and the interactions among three independent variables: time, the degree of matching for major histocompatibility complex antigens, and the treatment of the graft (whether it was fresh or frozen). These three independent variables had profound effects on the pattern, rate, and quality of the incorporation of the graft. Two-way and three-way interactions among these variables were also noted. Serial changes in every dependent variable were observed with time. Systemic antibody specific for donor antigens was measurable only in the serum of animals that had a major mismatch, but freezing markedly attenuated the systemic antibody response. Revascularization was profoundly affected by histocompatibility-antigen matching; the syngeneic grafts were revascularized more quickly and to a greater degree than the grafts with either a minor or a major mismatch. Freezing significantly (p < 0.001) reduced the revascularization of the syngeneic grafts but had no discernible effect on the grafts with a minor mismatch.

Telemetric force measurements across the hip after total arthroplasty.

A telemeterized total hip prosthesis was implanted in one patient and force-data were obtained. Thirty-one days postoperatively, the magnitude of the joint-contact force during double-limb stance was 1.0 times body weight. During ipsilateral single-limb stance the joint-contact force was 2.1 times body weight, and during the stance phase of gait the peak force typically was 2.6 to 2.8 times body weight, with the resultant force located on the anterosuperior portion of the ball. During stair-climbing, the force was 2.6 times body weight. At peak loads, the angle between the resultant force and the axis of the neck was 30 to 35 degrees and that between the resultant force and the plane of the prosthesis was 20 degrees. During stair-climbing or straight-leg raising, the out-of-plane orientation of the resultant force increased substantially. These data provide information concerning the forces that must be sustained by prosthetic hip joints during a number of common activities of daily living within the first month after implantation. The results also provide insight into the progression of early recovery and demonstrate the variety of forces that are generated during this period.

A dynamic optimization technique for predicting muscle forces in the swing phase of gait.

The muscle force sharing problem was solved for the swing phase of gait using a dynamic optimization algorithm. For comparison purposes the problem was also solved using a typical static optimization algorithm. The objective function for the dynamic optimization algorithm was a combination of the tracking error and the metabolic energy consumption. The latter quantity was taken to be the sum of the total work done by the muscles and the enthalpy change during the contraction. The objective function for the static optimization problem was the sum of the cubes of the muscle stresses. To solve the problem using the static approach, the inverse dynamics problem was first solved in order to determine the resultant joint torques required to generate the given hip, knee and ankle trajectories. To this effect the angular velocities and accelerations were obtained by numerical differentiation using a low-pass digital filter. The dynamic optimization problem was solved using the Fletcher-Reeves conjugate gradient algorithm, and the static optimization problem was solved using the Gradient-restoration algorithm. The results show influence of internal muscle dynamics on muscle control histories vis a vis muscle forces. They also illustrate the strong sensitivity of the results to the differentiation procedure used in the static optimization approach.

Comparison of damage accumulation measures in human cortical bone.

Elastic modulus degradation, strength reduction, and energy dissipation have traditionally been the properties of choice to monitor the damage process in cortical bone. However, these properties only provide limited insight into the damage process given the complex mechanical nature of bone. In the current study, alternative measures of the damage process were investigated for machined human cortical bone specimens loaded under torsion. Seventy-two bone specimens from 6 human femurs were subjected to a series of torsional relaxation cycles in which damage was induced during a single relaxation cycle and the effects of damage on the elastic, yield, viscous, and failure properties were determined from pre- and post-damage relaxation cycles. The results revealed that degradation of all torsion properties exhibited a significant twist magnitude effect. However, the yield stress and strain, the relaxation rate, and the total relaxation exhibited 5-10 fold greater degradation than both strength and modulus, when residual strength tests were conducted at high shear strain rates. For the loading conditions examined in this study, the results indicated that the relaxation and yield properties of cortical bone are more sensitive to shear damage accumulation and better measures of the damage process than either strength or modulus. Further, the results reveal an important interaction between damage and the viscous behavior of bone which provides new insight into the effects of damage on bone mechanical properties.

The biomechanical behavior of healing canine radii and ribs.

An experimental study and accompanying theoretical study of the biomechanics of healing canine ribs and radii have been conducted. Biomechanical behavior of the healing bones was determined experimentally by whole bone structural tests in four point bending. The experimental results indicated that the non-weight-bearing ribs regained bending stiffness more rapidly than bending stiffness, while the weight-bearing radii regained bending stiffness more rapidly than bending strength. These differences were not found to correlate with differences in overall callus biochemistry, but physical examinations of the bone suggested that differences in callus morphological details between the two bone types might offer an explanation. Utilizing a theoretical model, a parameter study of the influence of callus geometry and morphology on bending behavior was conducted. The results of the parameter study demonstrate that the experimentally observed variations in the amount and distribution of callus materials and in bone geometry can produce the qualitative biomechanical differences measured experimentally. The results of the parameter study also demonstrate that bending stiffness must be used with caution as a healing criterion since it does not necessarily reflect structural strength.