A common type of human injury occurs when a finger or toe is smashed, such as by an inadvertent hammer blow, door slam, etc. A result of these accidents is a very painful bruise and swelling under the nail, called a subungual hematoma.
In order to relieve the swelling under the nail, the nail is perforated to permit blood or other body fluids to ooze out to relieve pressure. By directing the pooling blood out of the restricted space under the nail, several beneficial results occur. First, the pressure under the nail is relieved so that the swelling and throbbing pain is reduced. Second, discoloration of the nail is lessened. Finally, premature loss of the nail is avoided. In the prior art, the nail has been perforated by burning the nail with a red-hot wire, or by puncturing with the tip of a hypodermic needle. A problem is lack of control: the delicate tissue under the nail can also be perforated, which can lead to additional pain and worsening of the wound.
Nail boring devices (called trephinators) are known in the art. U.S. Pat. No. 6,015,418 and US Patent Application 2006/0225757 describe hand drills for drilling a pressure-relief hole in the nail (2006/0225757 also has an electrically powered drill). However, there is no provision of making sure the drill does not inadvertently puncture the tissue under the nail.
U.S. Pat. No. 5,645,554 attempts to provide depth controlling means so that the drill does not inadvertently puncture the tissue under the nail. The depth controlling means is a tube which is added to a standard drill bit. It is placed around the bit and has an internal circular side wall, which is engaged with one or more flutes of the drill. The enables the tube to move longitudinally along the drill as the tube rotates on the drill.