Mechanisms of injuries

Injuries can arise from different mechanisms, and their causes can be diverse. Here are some common mechanisms of injury:

  1. Trauma: Trauma is one of the most common mechanisms of injury. It involves exposure to a force or impact that exceeds the capacity of the body’s tissues to resist. Examples of trauma include falls, blows, car accidents, sports injuries, or violence.
  2. Repetitive Injuries: These injuries result from repeated movements or exertion on certain parts of the body. Examples include inflammation of muscles, tendons, or joints due to repetitive movements or poor technique during a particular activity.
  3. Overuse Injuries: Overuse injuries occur when the body’s tissue becomes overworked or unable to withstand increased stress over time. Examples include stress fractures, tendinitis, or overuse muscle injuries.
  4. Heat Injuries: Extreme temperatures, such as burns from hot surfaces or frostbite from cold exposure, can also cause injury.
  5. Infection: Infection can lead to injury if pathogenic microorganisms penetrate body tissues and stimulate an inflammatory reaction. Examples include wound infections, abscesses or pneumonia.
  6. Chemical damage: Exposure to harmful chemicals can cause tissue damage, such as chemical burns or skin, eye or respiratory irritation.

It is important to note that the mechanisms of injury are diverse and can be combined in complex situations. Any injury requires careful evaluation and appropriate medical care to minimize the consequences and facilitate a speedy recovery.

Effective management of trauma victims in the out-of-hospital setting relies on the identification of injuries and potential injuries, as well as the provision of appropriate care. Unrecognized or unexpected injuries can lead to serious consequences, especially when diagnosed only after compensatory mechanisms have been exhausted. Evaluating the mechanism of injury allows suspicion to aid in the search for injuries.

To assess the mechanism of injury, knowledge of kinematics is required. Kinematics is a branch of mechanics that studies the movement of bodies regardless of the cause of that movement. Kinematics in trauma is the process of assessing the mechanism of injury caused by movement and changes in the movement of events. This process is based on several fundamental principles of physics:

Newton’s first law of motion (the law of inertia) states that an object will remain at rest or in uniform straight motion until an external force causes it to change its state.

Example: a collision with an object stops the forward movement of the vehicle. The vehicle stops, but the human body does not, until it hits the steering column, windshield, or instrument panel. The body and head stop, but the internal organs do not until they hit an obstacle or are stopped by their connective ligaments.

The law of conservation of energy explains why sudden stopping or starting results in injury because it states that energy can be transformed from one form to another, but cannot be created or destroyed. Vehicle motion is a form of energy, and when it stops or moves, that energy must be transformed into another form.

Example: during braking, the kinetic energy of a moving vehicle is converted into thermal energy. In a collision with a solid object, the motion stops abruptly and the kinetic energy is converted into mechanical energy that deforms the vehicle, the struck object, or both.

Kinetic energy depends on mass and speed (Ek = m/2 x v2). Speed ​​has a greater influence on the creation of kinetic energy. The kinetic energy of movement must be absorbed at the moment of impact. The abstraction of kinetic energy is a fundamental component of creating injuries. The type of injury also depends on the energy-absorbing tissue characteristics.

The creation of injury is also significantly dependent on the stopping path. For example, before a collision, both the vehicle and the driver inside it are moving at the same speed, but both decelerate to a stop together. The greater the deceleration, the greater the force acting on the driver’s body. The longer the stopping distance, the lower the deceleration, resulting in proportionally less injury. The inverse relationship between stopping distance and injury severity may also apply to falls. A person has a better chance of survival if they fall from the same height onto a compressed surface, such as deep snow (a compressed surface with a longer stopping distance), as opposed to falling onto a hard surface.

The basic mechanisms of energy exchange are relatively simple. When a moving object collides with a human body, or when a moving human body collides with an object, the tissues in the body are displaced, creating a cavity. This process is called cavitation and can create two types of cavities:

  1. Temporary cavities are created at the moment of impact and depend on the elasticity of the tissue.
  2. Permanent voids are also formed at the moment of impact and are caused by compression, tearing and, to some extent, stretching of the tissue.

Energy exchange directly depends on the tissue density (higher density tissue – more particles – more energy exchange – more damage) and the size of the impact area (which can be changed by the size of the object, its movement inside the body, fragmentation, etc.) at the point of contact between the object and human body.

Injuries caused by movement can be caused by the mechanical action of blunt or sharp forces. There are two main mechanisms of motion-induced injury:

  1. Injuries caused by the mechanical action of blunt forces: Rapid forward deceleration (e.g. vehicle collision) Sudden vertical deceleration (e.g. falls) Energy transfer from blunt objects (e.g. baseball bat)
  2. Injuries caused by the mechanical action of sharp forces: Projectiles Sharp objects (most often knives) Falls on solid objects (e.g. fences)

By examining the scene of the incident or examining the patient and those present, it is possible to assess the mechanism of injury that caused the injuries. Two key guidelines to consider are:

  1. What happened?
  2. How was the injury sustained?


Two forces are involved in the collision: tearing and compression.

Tearing occurs due to faster changes in the velocity of one organ or structure compared to the velocity of another organ or structure.

Compression results from direct pressure between organs or structures.


In vehicle collisions, including motorcycles, injuries are most often caused by blunt forces (although sharp forces or a combination of both can occur) due to rapid forward deceleration. There is a significant relationship between the severity of injuries and the change in vehicle speed (ΔV).

Examples include:

  • Vehicle-Vehicle Collision: The human body continues to move forward at the speed of the vehicle until the body comes to rest against an object inside the vehicle or outside.
  • Vehicle-pedestrian collision: The body is hit by the vehicle, and the head may hit the hood or windshield.
  • Falling from the vehicle: This happens when the passenger’s body is pushed out of the vehicle.

A more serious collision results in greater deceleration. If the speed of the vehicle decreases quickly, the body is exposed to a significant force. When a vehicle comes to an abrupt stop, as in a head-on collision, the unfastened human body continues to move at the vehicle’s speed until it is stopped abruptly by a rigid object inside the vehicle (eg, steering wheel, windshield, or dashboard). In contrast, the body stops abruptly in contact with a solid object outside the vehicle (eg another vehicle or a fixed object). During the deceleration process, temporary cavities are formed inside the human body.


In the context of falls, injuries are caused by rapid deceleration, particularly sudden vertical deceleration.

Examples of crashes include:

  • Falls from heights: Falls from elevated positions can result in serious injury due to rapid deceleration. The same principles apply, but the stopping distance varies, affecting the severity of injuries. A person has a better chance of survival if they fall from the same height onto a compressible surface, such as deep snow (a compressible surface with a longer stopping distance), as opposed to falling onto a hard surface.
  • Falls on the same level (slips and trips): Slips, trips and falls on the same level can also result in injuries. In these cases, people usually hit the ground less quickly, so the injuries are less serious.

The severity of the injury depends on the distance of the fall, the type of surface hit and the position of the body at the time of impact. Falls can cause injuries throughout the body, some of the most common being hip, wrist and forearm fractures, as well as traumatic brain injuries.


Injuries caused by the mechanical action of blunt objects include the transfer of energy from these objects to the human body. The amount of energy transferred depends on several factors, such as the size, shape and material of the object, the speed of the object, and the area of ​​impact on the body.

Examples include:

  • Baseball bat swing: A baseball bat swing transfers energy to the body. The amount of energy transferred is affected by the speed of the swing and the place of impact on the body. This can result in injuries such as fractures or contusions.
  • Falling on a step: Falling on a step can cause injury, especially if the contact of the body with the step is sudden and strong.
  • Assault with a blunt object: In cases of assault, attackers may use blunt objects, such as baseball bats, sticks, or other objects, to inflict injury on victims.

In these scenarios, energy is transferred from the blunt object to the body, causing injury. The severity and type of injuries depend on the above factors.

In summary, understanding the mechanisms of movement-related injuries is critical for healthcare, emergency responders, and safety professionals. The principles of kinematics and physics help explain how various types of injuries can occur, based on the laws of motion, energy exchange and tissue characteristics. This knowledge also helps in the assessment and treatment of traumatic injuries, ultimately improving patient care and outcomes.


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