Length of tunnel
Undermining is when a wound diameter is wider at its base (deep in the wound) than at the wound's skin edge.
For example, the hole in the skin may be 5mm, but the base of the wound cavity is 10mm. Tunneling is when the wound tracks under the skin to another opening in the skin or to a deeper cavity. Tunnels are sometimes referred to as a "sinus" or "tract".
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