Undermining is measured by inserting a probe under the wound edge directed almost parallel to the wound surface until resistance is felt. The amount of undermining is the distance from the probe tip to the point at which the probe is level with the wound edge. Clock terms are also used to identify the area of undermining.
Because tunneling and undermining are not readily visible, all wounds must he thoroughly probed to identify the full extent of tissue destruction. Wounds presenting with tunnels or undermining heal more slowly than wounds without these characteristics.