Q: If patient has a stab wound of the thigh extending into muscle (but not bone), what is the correct code and should it be assigned to the External ISS body region or the Extremity ISS body region?

A: The correct code is 816014.1 and the injury is assigned to the External ISS body region. Although the dictionary does inclue specific codes for muscle injuries in the Extremities chapters, those codes are intended for blunt injury. Penetrating injuries to the extremity that do not include injuries to specific underlying structures such as vessels or bone should be coded using the penetrating codes and assigned to the External body region for ISS purposes. The same rule for penetrating injuries applies to other regions of the body as well, with a few exceptions as noted in the AIS 2005 dictionary in the Head and Face chapters.