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Wednesday, February 28, 2001

Orthopaedists must learn basics of weaponry

Firearms catastrophes of accident or intention continue to make the headlines. Today's orthopaedic surgeon must be taught the basics of weaponry and penetrating injury, say authors of scientific exhibit 11, who have assembled some basic information on the subjects. They show that familiarization of ballistics predictably will influence wound treatment.

The kinetic energy theory for wounding capability (wound volume) of projectiles is: kinetic energy is proportional to 1/2 mass times velocity squared. Determinants of the wounding effects of the projectile include the velocity, mass, shape and stability of the missile, and its ability to expand or explode in the body.

The striking velocity of the missile is provided by the weapon. Low velocity weapons, e.g., 357 Magnum, 9 mm Beretta, allow a speed of the projectile of less than 2,000 feet per second (fps). The low velocity missile can pass through the body without significant soft tissue damage, leaving a small entrance and a small exit wound. By comparison, a crossbow produces a speed of only 58 meters per second. The arrow can possibly pass through the body, but often becomes impaled.

Although high velocity weapons give a speed to the projectile of greater than 2,000 fps. A 30-06 hunting rifle has this capability, however, military weapons such as the M-16 produce a speed of 3,200 fps. The pulsating temporary cavitation resulting from passage of a high velocity projectile creates a negative pressure that sucks in wound contaminants into the entrance and exit. The entrance wound is often punctate and the exit would is large.

The kinetic energy equation states that the mass does make a difference. A large missile from a low velocity weapon, particularly at close range, will cause extensive crushing in the wound. Altering the bullet structure to allow expansion once inside the body, e.g., "dum-dum" bullets, hollow-point bullets, and Short-stop® shot shell or to explode, e.g., Devastator bullets increases the wounding potential of the missile.

Treatment of extremity wounds from projectiles follow the wounding. Low energy wounds may be managed by debridement of the entrance and exit; limited antibiotics; and stabilization of the extremity. High energy wounds may require more extensive debridement with incision of both the entrance and exit wound to examine below the subfascial level for cavitation. Although removal of a bullet is not routinely advised unless it is intra-articular, bullets of the exploding variety which have not yet detonated should be removed. Surgeons should have a high index of suspicion if there is only one lead shot on X-ray and there are signs of black powder residue.

Coauthors of the study are Col. Kathleen A. McHale, MD; Cpt. Patrick Pollack, MD; and Christopher McHale, all of Walter Reed Hospital and Uniformed Services University of Health Sciences.

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Last modified 20/February/2001 by IS