ESWL is for the treatment of kidney stones that can block the flow of urine from the kidney causing pain and sometimes infection. A shock wave is focused on your kidney using X-Ray guidance. In order to transmit the shock wave through the skin, a rubber diaphragm is placed against your side and covered with a special gel. This does not require a surgical incision in the skin but there may be bruising on the skin surface where the shock waves enter the body.