Most emergency departments do not see much penetrating trauma. But it is helpful to be able to learn as much as possible from the appearance of these piercing injuries when you do see them. This post will describe the basics of reading stab wounds.

Important: This information will allow some basic interpretation of wounds. It will not qualify you as a forensics expert by any means. I do not recommend that you document any of this information in the medical record unless you have specific forensic training. You should only write things like “a wound was noted in the midepigastrium that is 2 cm in length.” Your note can and will be used in a court of law, and if you are wrong there can be significant consequences for the plaintiff or the defendant. This information is for your edification only.

1. What is the length of the wound? This does not necessarily correspond to the width of the blade. Skin stretches as it is cut, so the wound will usually retract to a length that is shorter than the full width of the blade.

2. Is the item sharp on one side or both? This can usually be determined by the appearance of the wound. A linear wound with two sharp ends is generally a two sided knife. A wound with one flat end and one sharp end is usually from a one-sided weapon. The picture below shows a knife wound with one sharp side.

3. Is there a hilt mark? This can usually be detected by looking for bruising around the wound. The picture below shows a knife wound with a hilt mark.

4. What is the angle? If both edges are symmetric, the knife went straight in. If one surface has a tangential appearance, then the knife was angled toward that side. You can approximate the direction of entry by looking at the tangential surface of the wound edge. In this example, the blade is angling upward toward the right.

5. How deep did it go? You have no way of knowing unless you have the blood stained blade in your possession. And yes, it is possible for the wound to go deeper than the length of the knife, since the abdominal wall or other soft tissues can be pushed inwards during the stab.

The algorithm for evaluating a stab to the anterior abdomen includes a number of different techniques for evaluation. In some cases where the chance of entry into the abdomen is thought to be low probability, endoscopic exploration can be used. What if a full thickness stab is detected, but the surgeon is able confirm that no abdominal injuries are present? Should the stab defect be closed?

There is no good data that tells us the incidence of ventral hernia from stab wounds. We do know that 10mm endoscopic port sites and larger can be the source of a ventral hernia and possible bowel obstruction after laparoscopic surgery, so it stands to reason (but be careful) that the same thing could happen with larger stabs. So why not close them?

A number of commercial devices have been developed for port site closure during endoscopic surgery (Carter Thomason Closure System, Cooper Surgical; Endo Close, Covidien). A group in Tokyo published a description of the technique using the former device to close the fascial defect of a self-inflicted stab wound.

Bottom line: This is an interesting use for a device used for closing more controlled stab wounds (surgical port sites) in less controlled ones. It seems fair to extrapolate our current experience from laparoscopic surgery to trauma in this case. I would be very interested to hear from anyone who is currently using this technique.

Reference: A quick and easy closure technique for abdominal stab wound after diagnostic laparoscopy. J Trauma 72(5):1448-1449, 2012.

As part of a thorough history and physical on any trauma patient, we typically ask “How big was the knife you were stabbed with?” and “How deep did it go?”

Unfortunately, the answers you typically will get are “This big!” while they hold their hands at least 3 feet apart, and “All the way, doc!”

These answers are not very helpful, so it is not really of much use to ask the questions. The “how big” question is not helpful at all, because a long knife may barely penetrate, and a paring knife can make it all the way into the heart.

This leaves the “how deep” question. There are two ways to determine the answer. If the paramedics or police bring the weapon in, you can carefully examine it (taking proper care to preserve forensic evidence) and see if there is a blood line extending from the tip. This will show the maximum depth of penetration.

The second way is to examine the wound, either by local wound exploration or using CT.

Helpful hint: You can’t tell how large (wide) the blade is by looking at the wound. The elastic nature of the skin causes it to stretch as it is being cut during the stab. When the knife is removed, the resulting laceration will always be less wide than the blade.