Study of the incidence of lacerations caused by blunt trauma

Status:

completed 04/2025

Aims:

Lacerations are open wounds to the superficial soft tissues, caused by blunt trauma to the body and resulting in the tissue layers tearing open. They are common in everyday life, for example as a result of falls, collision with objects or accidents in sports and at work. A laceration occurring at the workplace results in interruption of the work, consultation of a doctor, and a period possibly lasting several weeks until the wound has fully healed, during which a risk of inflammation also exists.

In 2018, lacerations constituted the second most common cause of workplace injury (20.4%), and the most common cause of injury in children’s daycare centres and during home/family childcare (35.8%). Nevertheless, little is known at present of the mechanism by which lacerations occur. In particular, no reliable body of data exists by which the severity of an injury could be estimated.

The objective of the project was to develop valid models for soft tissue exposed to blunt trauma. Such models enable computer-aided (finite element) simulations to be used for more detailed analysis of the mechanism by which an injury leads to formation of a laceration. The hypothesis of the research was as follows: the skin is torn open by the distension occurring during an impact as a result of the soft tissue being compressed against the underlying bone orthogonally to the force acting upon it. The formation of lacerations thus also depends on the behaviour of the deeper layers of soft tissue. In particular, the severity of injury was to be analysed in consideration of a number of influencing factors and anthropometric details. A database was thereby to be produced by which the severity of lacerations in a range of scenarios could be assessed. When implemented in preventive measures, this was to lead in the long term to a reduction in the severity of injuries.

Activities/Methods:

The project began with a comprehensive presentation of a number of aspects of lacerations. In particular, a survey was conducted of literature concerning the structure and material behaviour of the tissue layers involved (skin, fat, muscles). Based on this survey, material models for the individual tissue types were developed and implemented in a computer-aided (finite element) simulation environment.

In the course of the project, material models for skin, adipose tissue and muscle tissue were developed. These were then validated and optimized iteratively in simple load cases including tension (uniaxial, biaxial), compression (uniaxial) and shear, and also in complex load cases (drop tests). The anisotropic behaviour of skin was also taken into account. A total of over 450 real drop-tube tests were carried out on substitute tissue from animals. Together with data from the literature, these tests served as the basis for validating the material models. The preliminary study involving the drop-tube experiments was published in IFA Report 4/2023.

For skin, a failure model was also developed, based on the maximum principal strain. The models were then validated in a number of load scenarios in a multi-stage process. The results were validated against experimental data from the literature. Gaps in the data were filled by the use of ex-vivo tests on pig tissue. Over a thousand simulations have been carried out for extensive testing of both the material models and the failure model.

The models were used in a number of different simulation setups for systematic study of how various factors influence the mechanism by which lacerations occur. The risk of injury was visualized by the use of human models in typical scenarios. In addition, a database was created that can be used to assess the risk of laceration injuries at accident black spots.

Results:

A sensitivity study was conducted the scope of which included examination of the influence of the design parameters of the furniture, the boundary conditions of the accident scenario, and aspects of the injured person’s body on the incidence of lacerations. The body-related aspects (tissue thickness, bone structure and strength and the orientation of the Langer’s lines, i.e. tension lines in the skin) differ from one part of the body to another and according to the age of the study cohorts; the focus of these initial studies lay on children aged three. The velocities and masses involved are determined by the accident scenario. Two parameters relating to the furniture can be identified that can also be influenced in the context of preventive measures. These are, firstly, the edge radius, and secondly, the material (metal, wood, plastics) of which the furniture is made. Seven series of simulations serving as examples were carried out to examine the influence on a combination of skin and adipose tissue. Tissue samples with edge radii of between 2 mm and 60 mm were studied. The studies of the influence show that the maximum principal strain decreases with increasing radius. Depending on the boundary conditions, the difference between an edge radius of 2 mm and 10 mm is associated with a reduction of up to 20%. Decreasing strengths of the materials also cause a reduction in the skin’s maximum principal strain; however, this effect is less pronounced with a smaller radius, for example of 2 mm vs. 10 mm. More precise conclusions can be derived from the created database or can be calculated in the future with respect to the specific application scenario in question with use of the models developed. In addition, a THUMS human model (Total HUman Model for Safety, developed by the Toyota Motor Corporation and Toyota Central R&D Labs., Inc.) of a three-year-old child was used to visualize the accident scenario, a fall in which the forehead hit an item of furniture.

Other body regions (e.g. the shin) and other age groups can now also be examined in greater detail in further simulations. The models developed to date are not yet able to demonstrate failure in the deeper layers; this could constitute a future extension of the models. The results have been presented to the DGUV’s Subcommittee Children’s daycare facilities and daycare, and are to be given consideration when the relevant rules and regulations are revised.

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