Concretions can develop in certain parts of the body, such as in the kidneys, pancreas, ureter and gallbladder. It is common for biological concretions to be referred to as calculi or stones, especially when they are composed of mineral salts. For example, concretions formed in the biliary system are called gallstones. Those that form in the bladder are as also known as vesical calculi or bladder stones, and cystoliths. Calculi occurring in the kidney are often called kidney stones. Calculi can also occur in the ureter and are usually the result of the passage of stones originating in the kidney. Calculi are also present, for example, in salivary ducts or glands.
Lithotripsy is a popular, minimally invasive medical procedure that uses energy in various forms such as acoustic shock waves, pneumatic pulsation, electrical hydraulic shock waves, or laser beams to break up biological concretions. The force of the energy, when applied either extracorporeally or intracorporeally, usually in focused and continuous or successive bursts, comminutes a concretion into smaller fragments that may be extracted from the body or allowed to pass from the body.
There are several complications, however, which can result from lithotripsy. One problem with this procedure is that when concretions are fragmented, the fragments can become widely distributed. For example, when kidney stones are fragmented, the fragments can become widely distributed throughout the ureter and kidney. Therefore, during the procedure, it is desirable to confine the kidney stone and the resulting fragments within a constrained space. Various mechanical anti-migration backstops have been developed and involve the placement of these devices behind the kidney stone. Another approach, described in U.S. Patent Pub. No. 2005/0143678 involves the introduction of a temporary plug behind the stone, preventing the stone and its fragments from migrating further up the urethra or kidney.