How do microclimate factors affect the risk for superficial pressure ulcers: A mathematical modeling study

Evidence based synthesis for prevention of noninvasive ventilation related facial pressure ulcers

The last 2 decades have seen a growing trend towards the use of noninvasive ventilation (NIV) therapy in the management of many conditions that cause acute respiratory failure. However, there is a serious side effect that results in using these devices; the development of facial skin pressure damage, specifically pressure ulcers. This skin damage has a considerable effect on patients' quality of life, treatment adherence and patients' comfort in addition to the therapy challenges of wound care. The aim of this clinical review is to discuss the different characteristics of NIV interfaces and to provide evidence based recommendations to facilitate the selection and application of such interfaces to reduce NIV interfaces related pressure ulcers.

Technologies to monitor the health of loaded skin tissues

There are many situations where the skin and underlying soft tissues are compromised by mechanical loading in the form or pressure, or pressure in combination with shear. If sustained, this can lead to damage in the tissues particularly adjacent to bony prominences, resulting in chronic wounds. An array of bioengineering technologies have been adopted to assess the integrity of loaded soft tissues. This paper aims to review these approaches for the quantification, simulation and early detection of mechanically-induced skin damage. The review considers different measurements at the interface between the skin and support surface/medical device, involving pressure, shear, friction and the local microclimate. The potential of the techniques to monitor the physiological response of the skin to these external stimuli including biophysical measurement devices and sampling of biofluids are critically analysed. In addition, it includes an analysis of medical imaging technologies and computational modelling to provide a means by which tissue deformation can be quantified and thresholds for tissue damage defined. Bioengineering measurement and imaging technologies have provided an insight into the temporal status of loaded skin. Despite the advances in technology, to date, the translation to clinical tools which are robust and cost effective has been limited. There is a need to adapt existing technologies and simulation platforms to enable patients, carers and clinicians to employ appropriate intervention strategies to minimise soft tissue damage.

Investigating the effects of cervical collar design and fit on the biomechanical and biomarker reaction at the skin

Background

Research has shown that up to 33% of pressure ulcers (PUs) acquired in hospitals result from the application of a medical device. Cervical collars (C-collars) have been implicated in causing PUs, due to the mechanical force they apply to the skin. In order to improve our understanding of collar-related PUs, the present study aimed to assess the biomechanical, biochemical, and microclimate effects of C-collar design and fitting tension.

Methods

A cohort of 15 healthy volunteers was fit with two different C-collars according to the manufacturer guidelines. Two further collar tensions were also defined as loose and tight for each device. Each collar condition was applied for 15 minutes, with a 10 minute refractory period. Measurements at the device–skin interface included interface pressures, inflammatory biomarkers, microclimate, range of cervical motion, and comfort scores.

Results

The interface pressures at each tissue site increased monotonically with greater collar tension (p<0.01), irrespective of collar design. Biomarker analysis revealed that inflammatory cytokines (IL-1a) were elevated during collar application, with the highest increase during the tight fit condition, representing over a fourfold increase from unloaded conditions. Regardless of collar tension or type, there was an increase in temperature 1.5°C ±0.8°C compared to baseline values. Range of motion significantly decreased with greater strap tension (p<0.05), with an associated increase in discomfort.

Conclusion

The present findings revealed that increasing C-collar tensions caused elevated contact pressures at the device–skin interface, with a corresponding inflammatory response at the skin. These peak contact pressures were highest at the occiput, corresponding with reported PU locations. Devices should be designed to uniformly distribute pressures, and appropriate guidance is needed for their application.

On skin microrelief and the emergence of expression micro-wrinkles

Over the course of a life time, as a result of adaptive mechanobiological processes (e.g. ageing), or the action of external physical factors such as mechanical loading, the human skin is subjected to, and hosts complex biophysical processes. These phenomena typically operate through a complex interplay, that, ultimately, is responsible for the evolutive geometrical characteristics of the skin surface. Wrinkles are a manifestation of these effects. Although numerous theoretical models of wrinkles arising in multi-layered structures have been proposed, they typically apply to idealised geometries. In the case of skin, which can be viewed as a geometrically complex multi-layer assembly, it is pertinent to question whether the natural skin microrelief could play a significant role in conditioning the characteristics of compression-induced micro-wrinkles by acting as an array of geometrical imperfections. Here, we explore this question through the development of an anatomically-based finite strain parametric finite element model of the skin, represented as a stratum corneum layer on top of a thicker and softer substrate. Our study suggests that skin microrelief could be the dominant factor conditioning micro-wrinkle characteristics for moderate elastic modulus ratios between the two layers. Beyond stiffness ratios of 100, other factors tend to overwrite the effects of skin microrelief. Such stiffness ratio fluctuations can be induced by changes in relative humidity or particular skin conditions and can therefore have important implications for skin tribology.

Comparing the effects of 3 different pressure ulcer prevention support surfaces on the structure and function of heel and sacral skin: An exploratory cross-over trial

Special support surfaces are key in pressure ulcer prevention. The aim of this study was to measure the effects of 3 different types of mattresses (reactive gel, active alternating air, basic foam) on skin properties of the sacral and heel skin after 2 hours loading. Fifteen healthy females (median age 66 years) were included. Transepidermal water loss, skin surface temperature, erythema, stratum corneum hydration, epidermal hydration, skin extensibility, elastic function, and recovery as well as skin roughness parameters were measured under controlled room conditions before loading, immediately after loading, and 20 minutes post-loading in the supine position on the different mattresses. The highest increases in transepidermal water loss, skin temperature, and erythema were observed for the foam mattress after loading, indicating higher deformation and occlusion. Cutaneous stiffness decreased in all 3 groups, indicating structural changes during loading. There was a substantial decrease of mean roughness at the heel skin in the foam group, leading to a flattening of the skin surface. Study results indicate that the type of support surface influences skin structure and function during loading. The gel and air mattress appeared to be more protective compared with the foam mattress, but the differences between the gel and air were minor.

Effects of ambient conditions on the risk of pressure injuries in bedridden patients-multi-physics modelling of microclimate

Scientific evidence regarding microclimate and its effects on the risk of pressure ulcers (PU) remains sparse. It is known that elevated skin temperatures and moisture may affect metabolic demand as well as the mechanical behaviour of the tissue. In this study, we incorporated these microclimate factors into a novel, 3-dimensional multi-physics coupled model of the human buttocks, which simultaneously determines the biothermal and biomechanical behaviours of the buttocks in supine lying on different support surfaces. We compared 3 simulated thermally controlled mattresses with 2 reference foam mattresses. A tissue damage score was numerically calculated in a relevant volume of the model, and the cooling effect of each 1°C decrease of tissue temperature was deduced. Damage scores of tissues were substantially lower for the non-foam mattresses compared with the foams. The percentage tissue volume at risk within the volume of interest was found to grow exponentially as the average tissue temperature increased. The resultant average sacral skin temperature was concluded to be a good predictor for an increased risk of PU/injuries. Each 1°C increase contributes approximately 14 times as much to the risk with respect to an increase of 1 mmHg of pressure. These findings highlight the advantages of using thermally controlled support surfaces as well as the need to further assess the potential damage that may be caused by uncontrolled microclimate conditions on inadequate support surfaces in at-risk patients.

The use of prophylactic dressings in the prevention of pressure ulcers: a literature review

Pressure ulcers pose a significant burden to both patients and health care resources. There are an increasing number of studies that have examined the use of prophylactic dressings, and their ability to redistribute pressure and protect the skin from shear and friction damage. This literature review examines six studies conducted on this controversial subject. Brindle and Wegelin ( 2012 ; Chaiken, 2012 ; Cubit et al, 2012 ; Santamaria et al, 2012) all examined the role of dressings to prevent pressure ulcers, and Call et al (2013a ; 2013b ), conducted in vitro research into the mode of dressings. Current research suggests that while further research is required, the use of prophylactic dressings have a place alongside standard measures, in helping to prevent pressure, shear and friction damage.

Efficacy and safety of a new coverlet device on skin microclimate management: a pilot study in critical care patients

OBJECTIVE

To test the effect of a new coverlet device, allowing air circulation at the body/underlying surface interface, on skin microclimate management.

METHOD

This prospective observational pilot study took place in a 15-bed university-affiliated intensive care unit. Overall, 34 mechanically ventilated patients were included. Skin humidity and temperature were monitored before and after the implementation of the tested device at the occiput, scapulas, buttocks and sacrum. Humidity and temperature were evaluated through surface skin impedance and an infra-red thermometer, respectively. Health professionals were asked to evaluate the device.

RESULTS

After implementation of the coverlet device, there was a rapid, sustained and significant decrease in skin humidity at all sites ranging from 6 % to 15 %, excluding the occiput. Skin temperature also significantly decreased from 1 % at both scapulas, but not at the other studied body sites. No side effects were observed. Health professionals reported that the device was easy and quick to install. Although they did not report a subjective improvement in skin moisture or temperature, they considered the device to be efficient.

CONCLUSION

Although limited by its design, this pilot study suggests a good efficacy of the studied device on skin microclimate management. Further data are warranted to test the clinical implications of our findings.

Skin Microstructure is a Key Contributor to Its Friction Behaviour

Due to its multifactorial nature, skin friction remains a multiphysics and multiscale phenomenon poorly understood despite its relevance for many biomedical and engineering applications (from superficial pressure ulcers, through shaving and cosmetics, to automotive safety and sports equipment). For example, it is unclear whether, and in which measure, the skin microscopic surface topography, internal microstructure and associated nonlinear mechanics can condition and modulate skin friction. This study addressed this question through the development of a parametric finite element contact homogenisation procedure which was used to study and quantify the effect of the skin microstructure on the macroscopic skin frictional response. An anatomically realistic two-dimensional image-based multilayer finite element model of human skin was used to simulate the sliding of rigid indenters of various sizes over the skin surface. A corresponding structurally idealised multilayer skin model was also built for comparison purposes. Microscopic friction specified at skin asperity or microrelief level was an input to the finite element computations. From the contact reaction force measured at the sliding indenter, a homogenised (or apparent) macroscopic friction was calculated. Results demonstrated that the naturally complex geometry of the skin microstructure and surface topography alone can play as significant role in modulating the deformation component of macroscopic friction and can significantly increase it. This effect is further amplified as the ground-state Young's modulus of the stratum corneum is increased (for example, as a result of a dryer environment). In these conditions, the skin microstructure is a dominant factor in the deformation component of macroscopic friction, regardless of indenter size or specified local friction properties. When the skin is assumed to be an assembly of nominally flat layers, the resulting global coefficient of friction is reduced with respect to the local one. This seemingly counter-intuitive effect had already been demonstrated in a recent computational study found in the literature. Results also suggest that care should be taken when assigning a coefficient of friction in computer simulations, as it might not reflect the conditions of microscopic and macroscopic friction one intends to represent. The modelling methodology and simulation tools developed in this study go beyond what current analytical models of skin friction can offer: the ability to accommodate arbitrary kinematics (i.e. finite deformations), nonlinear constitutive properties and the complex geometry of the skin microstructural constituents. It was demonstrated how this approach offered a new level of mechanistic insight into plausible friction mechanisms associated with purely structural effects operating at the microscopic scale; the methodology should be viewed as complementary to physical experimental protocols characterising skin friction as it may facilitate the interpretation of observations and measurements and/or could also assist in the design of new experimental quantitative assays.

Soft silicone foam dressing is more effective than polyurethane film dressing for preventing intraoperatively acquired pressure ulcers in spinal surgery patients: the Border Operating room Spinal Surgery (BOSS) trial in Japan

Preventing intraoperatively acquired pressure ulcers (IAPUs) in patients undergoing spinal surgery in the prone position using a Relton-Hall frame is challenging. We investigated the efficacy of soft silicone foam dressings in preventing IAPUs. A prospective dual-center sham study was conducted among patients undergoing elective spinal surgery in a general hospital and a university hospital in Japan. The incidence of IAPUs that developed when soft silicone foam dressings and polyurethane film dressings were used was compared on two sides in the same patient. IAPUs developed on the chest in 11 of 100 patients (11%). Polyurethane film dressings were associated with a significantly higher rate of IAPUs than soft silicone foam dressings (11 versus 3, P = 0·027). A multivariate logistic regression analysis revealed that a diastolic blood pressure of <50 mmHg (P = 0·025, OR 3·74, 95% confidence interval [CI] 1·18-13·08) and the length of surgery (by 1 hour: P = 0·038, OR 1·61, 95% CI 1·03-2·64) were independently associated with the development of IAPUs. The use of soft silicone foam dressings reduced the risk of IAPUs (P = 0·019, OR 0·23, 95% CI 0·05-0·79) and was more effective than film dressings for preventing IAPUs in spinal surgery patients.

An evaluation of fluid immersion therapy for the prevention of pressure ulcers

BACKGROUND

Individuals with impaired mobility can spend prolonged periods on support surfaces, increasing their risk of developing pressure ulcers. Manufacturers have developed mattresses to maximise contact area. The present study evaluated both the biomechanical and physiological responses to lying postures on a Fluid Immersion Simulation mattress.

METHODS

Seventeen healthy participants were recruited to evaluate the mattress during three prescribed settings of immersion (high, medium and low). Parameters reflecting biomechanical and physiological responses, and the microclimate were monitored during three postures (supine, lateral and high-sitting) over a 90minute test session. Transcutaneous oxygen and carbon dioxide gas responses were categorised according to three criteria and data were compared between each condition.

FINDINGS

Results indicated that interface pressures remained consistent, with peak sacral values ranging from 21 to 27mmHg across all immersion settings and postures. The majority of participants (82%) exhibited minimal changes in gas tensions at the sacrum during all test conditions. By contrast, three participants exhibited decreased oxygen with increased carbon dioxide tensions for all three immersion settings. Supine and high sitting sacral microclimate values ranged between 30.1-30.6°C and 42.3-44.5% for temperature and relative humidity respectively. During lateral tilt there was a reduction of 1.7-2.5°C and 3.3-5.3% in these values. The majority of participants reported high comfort scores, although a few experienced bottoming out during the high-sitting posture at the high immersion setting.

INTERPRETATION

Fluid Immersion Simulation provides an intelligent approach to increase the support area. Further research is required to provide evidence based guidance on the use of personalised support surfaces.

Investigating the effects of strap tension during non-invasive ventilation mask application: a combined biomechanical and biomarker approach

Non-invasive ventilation is commonly used for respiratory support. However, in some cases, mask application can cause pressure ulcers to specific features of the face, resulting in pain and reduced quality of life for the individual. This study investigated the effects of mask strap tension on the biomechanical and biomarker responses at the skin interface. Healthy participants (n = 13) were recruited and assigned two different masks in a random order, which were fitted with three strap conditions representing increments of 5 mm to increase tension. Masks were worn for 10 minutes at each tension followed by a 10-minute refractory period. Assessment at the device–skin interface included measurements of pressures at the nose and cheeks, temperature and humidity, a selection of inflammatory cytokine concentrations collected from sebum and scores of comfort. The results indicated significantly higher interface pressures at the bridge of the nose compared to the cheeks for both masks (p < 0.05), with nasal interface pressures significantly increasing with elevated strap tension (p < 0.05). One inflammatory cytokine, IL-1α, increased following mask application at the highest tension, with median increases from baselines ranging from 21 to 33%. The other cytokines revealed a less consistent trend with strap tension. The participants reported statistically greater discomfort during elevated strap tension. Temperature and humidity values under the mask were elevated from ambient conditions, although no differences were observed between mask type or strap tension. The bony prominence on the bridge of the nose represented a vulnerable area of skin during respiratory mask application. This study has shown that mask strap tension has a significant effect on the pressure exerted on the nose. This can result in discomfort and an inflammatory response at the skin surface. Further studies are required to investigate respiratory mask application for appropriate individuals with comorbidities.

Thermoelastic modelling of the skin at finite deformations

The modelling and computation of the coupled thermal and mechanical response of human skin at finite deformations is considered. The model extends current thermal models to account for thermally- and mechanically-induced deformations. Details of the solution of the highly nonlinear system of governing equations using the finite element method are presented. A representative numerical example illustrates the importance of considering the coupled response for the problem of a rigid, hot indenter in contact with the skin.

Automatic limb identification and sleeping parameters assessment for pressure ulcer prevention

Pressure ulcers (PUs) are common among vulnerable patients such as elderly, bedridden and diabetic. PUs are very painful for patients and costly for hospitals and nursing homes. Assessment of sleeping parameters on at-risk limbs is critical for ulcer prevention. An effective assessment depends on automatic identification and tracking of at-risk limbs. An accurate limb identification can be used to analyze the pressure distribution and assess risk for each limb. In this paper, we propose a graph-based clustering approach to extract the body limbs from the pressure data collected by a commercial pressure map system. A robust signature-based technique is employed to automatically label each limb. Finally, an assessment technique is applied to evaluate the experienced stress by each limb over time. The experimental results indicate high performance and more than 94% average accuracy of the proposed approach.

A randomised controlled trial of the effectiveness of soft silicone multi-layered foam dressings in the prevention of sacral and heel pressure ulcers in trauma and critically ill patients: the border trial

The prevention of hospital acquired pressure ulcers in critically ill patients remains a significant clinical challenge. The aim of this trial was to investigate the effectiveness of multi-layered soft silicone foam dressings in preventing intensive care unit (ICU) pressure ulcers when applied in the emergency department to 440 trauma and critically ill patients. Intervention group patients (n = 219) had Mepilex(®) Border Sacrum and Mepilex(®) Heel dressings applied in the emergency department and maintained throughout their ICU stay. Results revealed that there were significantly fewer patients with pressure ulcers in the intervention group compared to the control group (5 versus 20, P = 0·001). This represented a 10% difference in incidence between the groups (3·1% versus 13·1%) and a number needed to treat of ten patients to prevent one pressure ulcer. Overall there were fewer sacral (2 versus 8, P = 0·05) and heel pressure ulcers (5 versus 19, P = 0·002) and pressure injuries overall (7 versus 27, P = 0·002) in interventions than in controls. The time to injury survival analysis indicated that intervention group patients had a hazard ratio of 0·19 (P = 0·002) compared to control group patients. We conclude that multi-layered soft silicone foam dressings are effective in preventing pressure ulcers in critically ill patients when applied in the emergency department prior to ICU transfer.

A mechanistic insight into the mechanical role of the stratum corneum during stretching and compression of the skin

The study of skin biophysics has largely been driven by consumer goods, biomedical and cosmetic industries which aim to design products that efficiently interact with the skin and/or modify its biophysical properties for health or cosmetic benefits. The skin is a hierarchical biological structure featuring several layers with their own distinct geometry and mechanical properties. Up to now, no computational models of the skin have simultaneously accounted for these geometrical and material characteristics to study their complex biomechanical interactions under particular macroscopic deformation modes. The goal of this study was, therefore, to develop a robust methodology combining histological sections of human skin, image-processing and finite element techniques to address fundamental questions about skin mechanics and, more particularly, about how macroscopic strains are transmitted and modulated through the epidermis and dermis. The work hypothesis was that, as skin deforms under macroscopic loads, the stratum corneum does not experience significant strains but rather folds/unfolds during skin extension/compression. A sample of fresh human mid-back skin was processed for wax histology. Sections were stained and photographed by optical microscopy. The multiple images were stitched together to produce a larger region of interest and segmented to extract the geometry of the stratum corneum, viable epidermis and dermis. From the segmented structures a 2D finite element mesh of the skin composite model was created and geometrically non-linear plane-strain finite element analyses were conducted to study the sensitivity of the model to variations in mechanical properties. The hybrid experimental-computational methodology has offered valuable insights into the simulated mechanics of the skin, and that of the stratum corneum in particular, by providing qualitative and quantitative information on strain magnitude and distribution. Through a complex non-linear interplay, the geometry and mechanical characteristics of the skin layers (and their relative balance), play a critical role in conditioning the skin mechanical response to macroscopic in-plane compression and extension. Topographical features of the skin surface such as furrows were shown to act as an efficient means to deflect, convert and redistribute strain-and so stress-within the stratum corneum, viable epidermis and dermis. Strain reduction and amplification phenomena were also observed and quantified. Despite the small thickness of the stratum corneum, its Young׳s modulus has a significant effect not only on the strain magnitude and directions within the stratum corneum layer but also on those of the underlying layers. This effect is reflected in the deformed shape of the skin surface in simulated compression and extension and is intrinsically linked to the rather complex geometrical characteristics of each skin layer. Moreover, if the Young׳s modulus of the viable epidermis is assumed to be reduced by a factor 12, the area of skin folding is likely to increase under skin compression. These results should be considered in the light of published computational models of the skin which, up to now, have ignored these characteristics.

Dressings as an adjunct to pressure ulcer prevention: consensus panel recommendations

The formulation of recommendations on the use of wound dressings in pressure ulcer prevention was undertaken by a group of experts in pressure ulcer prevention and treatment from Australia, Portugal, UK and USA. After review of literature, they concluded that there is adequate evidence to recommend the use of five-layer silicone bordered dressings (Mepilex Border Sacrum(®) and 3 layer Mepilex Heel(®) dressings by Mölnlycke Health Care, Gothenburg, Sweden) for pressure ulcer prevention in the sacrum, buttocks and heels in high-risk patients, those in Emergency Department (ED), intensive care unit (ICU) and operating room (OR). Literature on which this recommendation is based includes one prospective randomised control trial, three cohort studies and two case series. Recommendations for dressing use in patients at high risk for pressure injury and shear injury were also provided.

Systematic review of the use of prophylactic dressings in the prevention of pressure ulcers

This systematic review considers the evidence supporting the use of prophylactic dressings for the prevention of pressure ulcer. Electronic database searches were conducted on 25 July 2013. The searches found 3026 titles and after removal of duplicate records 2819 titles were scanned against the inclusion and exclusion criteria. Of these, 2777 were excluded based on their title and abstract primarily because they discussed pressure ulcer healing, the prevention and treatment of other chronic and acute wounds or where the intervention was not a prophylactic dressing (e.g. underpads, heel protectors and cushions). Finally, the full text of 42 papers were retrieved. When these 42 papers were reviewed, 21 were excluded and 21 were included in the review. The single high-quality randomised controlled trial (RCT) and the growing number of cohort, weak RCT and case series all suggest that the introduction of a dressing as part of pressure ulcer prevention may help reduce pressure ulcer incidence associated with medical devices especially in immobile intensive care unit patients. There is no firm clinical evidence at this time to suggest that one dressing type is more effective than other dressings.

Modeling the Effects of Moisture-Related Skin-Support Friction on the Risk for Superficial Pressure Ulcers during Patient Repositioning in Bed

Patient repositioning when the skin is moist, e.g., due to sweat or urine may cause skin breakdown since wetness increases the skin-support coefficient of friction (COF) and hence also the shear stresses that are generated in the skin when the patient is being moved. This everyday hospital scenario was never studied systematically however. The aim of this study was to simulate such interactions using a biomechanical computational model which is the first of its kind, in order to quantitatively describe the effects of repositioning on the pathomechanics of moisture-related tissue damage. We designed a finite element model to analyze skin stresses under a weight-bearing bony prominence while this region of interest slides frictionally over the support surface, as occurs during repositioning. Our results show, expectedly, that maximal effective stresses in the skin increase as the moisture-contents-related COF between the skin and the mattress rises. Interestingly however, the rise in stresses for a wet interface became more prominent when the skin tissue was stiffer – which represented aging or diabetes. This finding demonstrates how the aged/diabetic skin is more fragile than a young-adult skin when repositioning in a moist environment. The modeling used herein can now be extended to test effects of different moisturizers, creams, lubricants, or possibly other interventions at the skin-support interface for testing their potential in protecting the skin from superficial pressure ulcers in a standard, objective, and quantitative manner.

Microclimate and development of pressure ulcers and superficial skin changes

This study aims to evaluate the microclimate and development of pressure ulcers and superficial skin changes. A prospective cohort study was conducted in an acute care ward in Indonesia. Risk factors for pressure ulcers and superficial skin changes were identified based on the Bergstrom Braden conceptual model. Microclimate data were collected every 3 days for 15 days while the development of pressure ulcers and superficial skin changes was observed every day. Pressure ulcers and superficial skin changes were developed in 20 of the 71 participants. Total mean difference in skin temperature was higher for patients with pressure ulcers and superficial skin changes (0·9 ± 0·6°C) compared with controls (0·6 ± 0·8°C) (P = 0·071). Binary logistic regression predictor values for pressure ulcers and superficial skin changes were 0·111 for type of sheet and 0·347 for Braden Scale results. In conclusion, difference in skin temperature seems to be a predictor for pressure ulcer development and superficial skin changes, while synthetic fibre sheets are able to maintain a beneficial microclimate.

Modeling mechanical strains and stresses in soft tissues of the shoulder during load carriage based on load-bearing open MRI

Shoulder strain is a major limiting factor associated with load carriage. Despite advances in backpack designs, there are still reports of shoulder discomfort, loss of sensorimotor functions, and brachial plexus syndrome. The current study is aimed at characterizing mechanical loading conditions (strains and stresses) that develop within the shoulder's soft tissues when carrying a backpack. Open MRI scans were used for reconstructing a three-dimensional geometrical model of an unloaded shoulder and for measuring the soft tissue deformations caused by a 25-kg backpack; subsequently, a subject-specific finite element (FE) model for nonlinear, large-deformation stress-strain analyses was developed. Skin pressure distributions under the backpack strap were used as reference data and for verifying the numerical solutions. The parameters of the model were adjusted to fit the calculated tissue deformations to those obtained by MRI. The MRI scans revealed significant compression of the soft tissues of the shoulder, with substantial deformations in the area of the subclavian muscle and the brachial plexus. The maximal pressure values exerted by a 25-kg load were substantial and reached ∼90 kPa. In the muscle surrounding the brachial plexus, the model predicted maximal compressive strain of 0.14 and maximal tensile strain of 0.13, which might be injurious for the underlying neural tissue. In conclusion, the FE model provided some insights regarding the potential mechanisms underlying brachial plexus injuries related to load carriage. The large tissue deformations and pressure hotspots that were observed are likely to result in tissue damage, which may hamper neural function if sustained for long time exposures.