Blunt Force Trauma
Types of Trauma
An outside force can be applied with sufficient impact to cause injury to an animal. In veterinary forensic science, two common types of forces and resulting traumas are blunt force trauma (BFT) and sharp force trauma (SFT). Sharp force trauma is addressed in Chapter 8.
In agreement with Munro and Munro, the author recommends dividing the discussion and description of BFT into two successive stages: (1) the description of the wound(s) and lesions as to their nature, extent and location, and then (2) any opinion and/or conclusions that can be drawn about these injuries as their cause, and whether the cause was accidental, nonaccidental, or undetermined (Munro & Munro, 2008).
BFT is the application of an outside or external force to an animal by a non-sharp object. Ressel, Hetzel, and Ricci put forth the argument that there is a gray area between blunt and sharp force trauma but also make the very practical statement that “we apply the term blunt force trauma to all lesions caused by clearly non-sharp objects’’ (Ressel et al., 2016). The injuries from that result from BFT come from the transference of the kinetic energy from the moving object onto the body or from a moving body impacting a blunt object or a combination of the two (Gerdin, 2014). The classic equations are:
Force = Mass x Acceleration Kinetic Energy = Vi Mass x Velocity2
This transfer of energy can cause damage to the body at a macroscopic level (abrasion, contusion/ bruising, lacerations, and fractures) and at a microscopic level (cell injury and/or death). Therefore, a complete description of the effects of the trauma would include both levels.
The forces may act on the body through compression, tension, shearing, torsion, bending, or a combination of these (Gerdin, 2014). Compression pushes the tissues together, while tension pulls them apart. Bending is compression of tissue along one side, which tends to result in tension along the opposite side. Shear is a force that slides along the tissue at an angle, while torsion twists the tissue along its axis.
Although the amount of force certainly influences the extent of injuries, other factors may also be involved. These factors can include the time and surface area over which the impact occurs and the particular area of the body where the impact occurs.
The time over which the impact occurs can be a factor in at least two ways. The first is the time in which the impact is delivered to the body (i.e., the rate of impact) for a discrete incidence (Gerdin, 2014). For example, if the impact occurs over a sufficient length of time, the body may have sufficient time to stretch or otherwise adapt to the impact. In this scenario, the body may be able to absorb and dissipate the force (to a limited extent). These adaptations could minimize or at least lessen the effect of the impact to the animal’s body. An impact delivered at a faster rate would not allow the body to absorb/dissipate the force and would be more likely to result in failure of the tissue (laceration, fracture, etc.). The other consideration of time would be relevant in the case of an impact that is chronically applied to an area of the body. Common examples of this chronic impact are pressure sores seen over bony prominences of emaciated animals (Figure 7.1a,b). The amount of time the bony prominence is in contact with the hard, blunt surface (concrete floor, metal cage) may affect the depth and degree of severity of the lesions of the tissues in these regions.
The surface area over which the impact is delivered can also significantly affect the damage done to the tissue. If a strong force is applied over a relatively small surface area, the amount of transferred energy is concentrated onto fewer tissues with the potential for more catastrophic effects to those tissues than if the transferred energy is spread out to more tissues. By spreading out the energy transfer over a larger surface area, the energy transfer can be better absorbed or dissipated by the increased volume of tissues.
The area of the body impacted can vary tremendously in its ability to absorb the force from the impact. Impact to skin covering soft tissues such as muscles may not cause as extensive lesions as
Figure 7.1 (a) This emaciated dog, housed in an animal shelter for several months with little to no bedding, developed pressure sores, (b) Pressure sores also developed on the right front leg of the same dog.
the impact of the same force, duration, and surface area to skin covering bone such as the skull. In addition, some medical conditions of the animal such as brittle bone disease or connective tissue defects such as Ehlers—Danlos (Ettinger & Feldman, 2000) may affect the final outcome of the impact to the animal.
Other factors can also influence the final outcome to the animal of BFT. The site of the impact may mean the difference between the life and death of the animal. A force sufficient to fracture a femur may cause an abrasion to the skin, bruising, and hemorrhage to the subcutaneous and overlying muscles and fragmentation of the femur. Should the force impact the femur in such a way that the femoral artery is ruptured, then the impact may be fatal. The same can be said about BFT to the abdomen; the final outcome in these cases may depend not so much on the amount of force but rather on the location of the injuries caused by the force.
Studies have shown that blunt force trauma can have an effect on the coagulation abilities and processes of animals (Abelson et al., 2013; Gottlieb et al., 2017). The effect appears to be rare in animals suffering mild to minor BFT but may be significant with severe trauma (Abelson et al., 2013; Gottlieb et al., 2017). Assessment of activated partial thromboplastin time (aPTT) should be considered in the evaluation of animals suffering severe traumatic injuries, as it may be altered in animals suffering from severe BFT (Holowaychuk et al., 2014).
In the author’s training during and after veterinary school, any tear in the skin of an animal was referred to as a laceration and the term “incised wound” was rarely, if ever, used. For the sake of consistency here, the descriptions for typical lesions seen from BFT will be taken from the human medical forensic field. The most common lesions that are associated with BFT—abrasions, contusions, lacerations and fractures—are described in the following sections.
