Abrasions

An abrasion can be defined as an injury to the skin in which the epidermis has been partially or completely removed by friction against a rough surface or has been destroyed by compression (DiMaio & DiMaio, 2001; Ressel et al., 2016) (Figure 7.2). In some cases, the damage extends into the superficial dermal layer as well. Abrasions can be caused by blows, falls, dragging, scratching,

Figure 7.2 During a hoarding investigation, this abrasion was documented on the caudal surface of the leg of a dog.

rubbing, chafing, and/or indentation of the skin at the entry of a puncture wound (Figure 7.3a,b). Abrasions can be found in conjunction with other lesions such as contusions and lacerations.

Antemortem abrasions tend to be reddish brown, moist or scabbed, with blurred or indistinct margins, and may show evidence of an inflammatory reaction on histopathological examination. Healed abrasions do not show scarring (DiMaio & DiMaio, 2001). Postmortem abrasions tend to be yellow, translucent, dry surface without a scab, with sharp or well-demarcated edges and no evidence of inflammatory reaction on microscopic examination.

Depending on the angle of impact of the object with the body, abrasions can be subdivided into three categories: scrape, imprint, or contact and pattern (Ressel et al., 2016).

Scrape (or Brush) Abrasions

A scrape abrasion occurs when the object contacts the body at an angle other than 90 degrees (Ressel et al., 2016). One type of scrape abrasion, called a scratch, is caused by a pointed object moving across the skin at an angle. A typical example in veterinary medicine is a scratch by a toenail or tooth from another animal. In non-haired or lightly haired skin, if the object strikes the skin at an acute angle, it may tend to push and pile up skin cells. In these cases, the direction of the scratch can be determined as the starting point is denuded of cells, but the end point has the pile of cells where the object stopped contacting the skin (Munro & Munro, 2008). DiMaio contends that this directionality is more theoretical than practical (DiMaio & DiMaio, 2001).

As animals are often covered in hair, the hair coat of animals may diffuse the force of the scratch. Examination of the hair coat may show broken hair shafts. Because the object is moving across the hair and skin at an angle, the shape and size of the lesion may not necessarily correlate with the size and shape of the object (Gerdin, 2014).

A wide scratch abrasion may be called a graze. This type of abrasion can be associated with sliding and friction when the body tends to slide across a surface or an object slides across a large section of skin. One of the most common grazes in veterinary medicine is road rash from an animal being hit by a vehicle and sliding across the pavement. Another type of graze from friction would be the lesion caused by a collar, harness, or ligature rubbing with force and friction against the skin. These lesions should be examined closely for associated debris from the ground or pavement, or fibers from the object. Depending on the force of the friction, these pieces may be found embedded into the dermis (DiMaio & DiMaio, 2001; Gerdin, 2014; Merck, 2013).

If a scrape abrasion extends into the dermis, bleeding or fluid seepage may occur. When the fluid dries, it leaves a reddish-brown scab (DiMaio & DiMaio, 2001; Gerdin, 2014).

Figure 7.3 (a) Abrasion documented on the face of a dog. (b) All photographs should be made with and without a scale.

Impact (Contact) Abrasions

Impact abrasions occur when the blunt object impacts the animal perpendicularly (DiMaio & DiMaio, 2001; Ressel et al., 2016). The force impacts the body such that the tissue underneath the object is crushed. The location of the impact dictates the injury from this type of force. A dense hair coat may dissipate the force such that there is no visible lesion to the skin. If the site of impact is over a bony prominence such as the zygomatic arch or skull, an abrasion may be visible. If the site is over an area with underlying tissue such as muscle or bone, then the impact may produce a mixed trauma such as abrasion, contusion, and/or fracture of underlying bone.

Pattern Abrasions

A pattern abrasion is one in which the shape of the object can be determined by the impression it leaves on the body. The hair coat of animals tends to dissipate the impact of the object, although a distinct pattern might be visible in areas of bare skin or sparse hair coat. Depending on the object impacting the body, shaving the hair coat may reveal the pattern abrasion. A pattern abrasion can also be a scrape or impact type of abrasion. Ressel and Ricci (2016) describe how nail abrasions are the most common pattern abrasion in animals: circular nail marks from primates, crescent marks from human nails, and narrow elongated mark from canids. Their case material suggests that felids and birds of prey leave abrasions with lacerations or puncture wounds.