Correlation of Stab and Incised Wounds With Sharp Instrument

In some instances, a knife may be still in the individual (Fig. 6). In rare instances, the knife tip is broken from contact with bone and is revealed on a radiograph. Analysis showing the blood of the deceased on a suspected knife ties that weapon with the observed injuries (Fig. 7). If no knife is present, then postmortem measurements of the stab wound can, in a limited way, be linked with specific dimensions of the sharp instrument inflicting the injury. The stab wound depth, length, and width approximate the length, width, and thickness, respectively, of the weapon. These measurements assist investigators who, faced with a wide array of knives in a household, are able to focus their efforts in finding a weapon. Realizing that many knives can produce the wounds observed, the pathologist can usually only comment that the appearance and configuration of the wounds are consistent with a particular weapon. In contrast, sharp-edged instruments cannot be distinguished by incised wounds of varying lengths and depths. The measurement of an incision, including its depth, does provide information regarding severity of the injury.

An impaled object is embedded in the body (46). The end of the foreign body may have been cut at the scene by emergency personnel but left in place to ensure tamponade of internal injuries (47). Radiographs document the presence and position of the object. Its removal may require forceful manipulation and sawing (46).

The correlation of knife-blade and stab-wound dimensions can be altered by a number of factors:

Fig. 5. Suicide by table saw. (A) Victim found face down, flat on table with circular saw running. (B) Vertex of skull. Several saw cuts in different directions, some penetrating brain. (C) Incised wound of neck. Severed carotid arteries (tied). (Courtesy of Dr. D. King, Regional Forensic Pathology Unit, Hamilton, Ontario, Canada.)

Fig. 5. Suicide by table saw. (A) Victim found face down, flat on table with circular saw running. (B) Vertex of skull. Several saw cuts in different directions, some penetrating brain. (C) Incised wound of neck. Severed carotid arteries (tied). (Courtesy of Dr. D. King, Regional Forensic Pathology Unit, Hamilton, Ontario, Canada.)

Fig. 6. Self-inflicted abdominal stab wound. Knife in situ.
Circular Saw Wounds Wound Pictures

• Skin elasticity: The width of the stab wound is the least important measurement because most knife blades are in the order of 1- to 2-mm thick (about 0.0625 in.). If a wound is oriented parallel to tension lines created by skin elasticity (Langer's lines), then the wound is relatively narrow. A wound oriented perpendicular to lines of elasticity gapes. The length of a gaping skin wound is shortened (Fig. 8). Such a wound requires approximation of its edges to determine a more accurate length (72). One study observed that the lengths of skin wounds on the chest, abdomen, and flanks did not reach the full width of the blades, even after approximating the gaping edges (72).

• Angle of knife relative to skin surface: Many knife blades are single-edged, i.e., one sharp cutting edge and an opposite dull noncutting edge. Typically, when a knife is inserted perpendicular to the skin surface, one point of the resulting skin wound is sharp and the other blunt, conforming to the configuration of the blade edge (Fig. 9). If the blade is inserted at an angle, then the wound lengthens and both ends become sharp one corresponding to the entry initially of the tip of the knife and the other resulting from the following sharp blade edge (Fig. 9). The least "rocked" wound length corresponds to the blade width (Fig. 10). Movement of the knife and victim causes twisting of the knife blade, relative to its entry or exit, resulting in lengthening of the wound and possible notching of one end of the skin wound (Fig. 11). Considerable twisting of the knife leads to large, irregular injuries (Fig. 12). Multiple wound tracks are possible with a single cutaneous wound, if there has been re-entry or twisting of the knife (Fig. 13; refs. 2 and 73). Hemorrhage along single and multiple tracks indicates infliction before death (Fig. 14; ref. 10). Multiple tracks indicate intent (19).

• Anatomical variation (antemortem and postmortem): The wound depth provides important information about the blade length. In general, the deepest stab is a guide to the minimum blade length. The depth of a wound track can be altered after death. The postmortem measurement of the depth of a stab wound involving the anterior surface of the heart is only an approximate estimate of the blade length of the stabbing weapon (74). The removal of the sternum during autopsy results in detachment of the anterior

Fig. 8. Measurement of stab wound length. (A) Gaping stab wound. Length of wound shortened. (B) Stab wound edges apposed manually.
Fig. 9. Multiple stab wounds on chest. Perpendicular insertion of knife—sharp and blunt ends (arrow). Angled insertion—both ends sharp (arrowheads). (Courtesy of the Office of the Chief Medical Examiner, Chapel Hill, NC.)

Fig. 10. "Rocked" knife wound. (A) Gaping single stab wound of chest (below thoracotomy incision). Length of wound caused by relative movement of victim and knife. (B) Knife used to inflict injury. Note narrow blade width. (Courtesy of the Office of the Chief Medical Examiner, Chapel Hill, NC.)

Fig. 10. "Rocked" knife wound. (A) Gaping single stab wound of chest (below thoracotomy incision). Length of wound caused by relative movement of victim and knife. (B) Knife used to inflict injury. Note narrow blade width. (Courtesy of the Office of the Chief Medical Examiner, Chapel Hill, NC.)

part of the pericardium, which causes the heart to collapse back into the thoracic cavity. This increases the distance between the anterior chest surface and heart (7 mm or about 0.25 in. in one study [74]). If the track involves the heart, consequent hemoperi-cardium also increases the distance between the chest surface and the heart wound (1 to 4 cm or about 0.5 to 1.5 in. [74]). If there is cardiac tamponade, the heart stops in systole, resulting in an apparent deeper wound at autopsy than at the time of infliction, when the heart may have been in diastole (74).

• Degree of applied force: The width of a knife blade progressively decreases as it tapers toward its point. If a knife is inserted superficially only to the depth of its tapered segment, then the cutaneous wound length is less than the maximum blade width. Forcefully thrusting the knife into the chest or abdomen can result in a wound depth that exceeds the knife blade length. Because the knife is inserted its full length, secondary blunt trauma injuries can be seen around the cutaneous wound, corresponding to the so-called hilt of the knife (i.e., handle, hand guard, or device for fixing the open blade; see Fig. 15 and ref. 75). In a study of 74 deaths resulting from stabbing, only 5 cases having a hilt mark were observed (76). Thrust impact injury describes firm surfaces, other than the hilt of the knife (e.g., the edge of the hand holding the knife) causing marks on the skin (3). Individuals sustaining self-inflicted wounds can brace a knife by various means (e.g., leaning forward while grasping a knife, hammering a knife to the hilt; see Fig. 16 and ref. 9).

° The assessment of the degree of force required to penetrate the body is difficult to ascertain because of variables such as the sharpness of the weapon, the velocity at the moment the body is struck, the amount and nature of clothing worn, and the type of tissue penetrated (77-79). The sharpness of the tip of the weapon is considered

Fig. 11. Multiple stab wounds. Inferior wound "notched" (arrow) owing to twisting of knife blade. (Courtesy of the Office of the Chief Medical Examiner, Chapel Hill, NC.)

Fig. 12. Multiple stab wounds of different sizes. Large wound resulting from considerable twisting of knife blade. (Courtesy of the Office of the Chief Medical Examiner, Chapel Hill, NC.)

Fig. 13. Homicide. (A) Single stab wound on back. (B) Wound track continued into apex of right lower lobe of lung (arrow). (C) Multiple tracks at base of right lower lobe (arrows) indicating multiple insertions through same stab wound.
Fig. 14. Infanticide. Multiple stab wounds. (A) Stab wound, right neck. (B) Posterior neck dissection. Wound track extended into cervical spinal cord (autopsy arrowhead). Hemorrhage along track indicates victim was alive when wound inflicted.
Stab Wound Sharp Edge Blunt Edge
Fig. 15. "Hilt" mark caused by forceful thrusting of knife. Depth of wound exceeded length of blade. (A) Single stab wound of chest. Note two linear bruises (arrows) on either side of wound. (B) Bruises were caused by edges of wooden handle of knife that was forcefully thrust into victim.

the most important factor in allowing penetration. The pressure exerted by a single finger can be enough (77-79). A blunt tip requires more pressure and increases the possibility of associated blunt trauma injuries. Except for bone and calcified cartilage, skin has the greatest resistance to penetration. Once the skin is penetrated, little force is needed to penetrate further (77,78,80). Regional differences in penetrability exist (77). For example, the intercostal spaces are penetrated more easily than the upper abdomen because the tissues are more tightly stretched. Others have observed, using cadavers and amputation specimens, that there is significant resistance when muscle is penetrated (79,81).

° For a knife held either against the skin surface (stationary) or up to 15 cm (6 in.) away, 0.5 to 3 kg (1.1-6.6 lb) of pressure (0.5-3 N of force) is required to penetrate chest and abdominal skin (15,77,78). Knight observed the abdominal wall of an average-sized cadaver, when leaned forward 10 cm (4 in.) onto a firmly held knife, was easily penetrated supporting the scenario of "running onto" a knife (77). Green found that the skin of cadavers was also easily stabbed when a knife was held 15 cm (6 in.) away and suddenly pushed from behind (the "accidental stumble" [78]). A case report described a 42-yr-old man who committed suicide with a dagger (2.72 kg or 6 lb), which fell freely from a height of 10 cm (4 in.), penetrated the chest, and pierced the lung to a depth of about 12 cm (4.75 in. [15]). More force is generated when a knife is moving. Greater mean terminal velocity and energy are generated in overarm stabs compared with underarm stabs (82,83). Stabs inflicted perpendicular to the skin surface generate more force than angled thrusts (80).

° Instruments with pointed tips can penetrate fabric, when held by one hand, but pressure from both hands is required when using a less sharp object (e.g., screwdriver

Fig. 16. Stabbing suicide. (A) Victim braced knife against wall. Note faint gray marks (arrows), adjacent to blood spatter, from metal transfer from handle of knife. (B) Knife in body. Note gray metal at the end of the handle of knife.

[84]). A blunt weapon can injure skin without penetrating fabric, which can embed in the wound. Cuts with frayed edges imply a blunt or serrated weapon, but blood can bind fibers, causing edges to appear "neat." Green observed that pressure of 2 to 3 kg (4.4 to 6.6 lb), using a sharp weapon, could penetrate clothing (78).

° More effort may be required to remove a knife from a body (up to 15 kg or 33 lb of pressure in clothed cadavers [78]). This has implications regarding intent, if more than one wound is present (78). On the other hand, large forces were not required to remove a sharp blade from pig skin (79).

• Medical care: Prolonged hospitalization means wounds heal (Fig. 17). Medical interventions (e.g., thoracotomy) alter and create wounds (e.g., chest tube insertion; see Figs. 17 and 18). The pathologist must obtain accurate information from the medical record and clinical team to confidently assess the injuries observed.

Was this article helpful?

0 0

Post a comment