Ring Sequestrum- Plain Film

Late finding which is said to be pathognomonic of pin tract infection is "ring" sequestrum. The appearance of this finding is due to the particular geometry of a pin and pin tract. As a pin tract becomes infected, the bone immediately adjacent to the pin becomes infected first, and a certain amount of it dies. The viable bone adjacent to this infected dead bone then becomes hyperemic and becomes relatively osteopenic. The infected dead bone remains at its original density. Once the pin has been removed, if one looks directly down the pin tract with a radiograph, this cylinder of dead bone looks like a "ring".