Tetanus is a very serious bacterial infection that is caused by a bacteria that lives in the soil and that often contaminates rusty surfaces, like a rusty nail. The lay term for tetanus infection is 'lockjaw' because in the late stages of tetanus all of the muscles seize up and become stiff. Once tetanus progresses to this stage, it is very difficult to treat and is often fatal.
For this reason, it is always recommended that whenever you have an injury
caused by a rusty nail or other dirty object you go to see your doctor
right away. Fortunately the incidence of tetanus is very low, because most of us have been vaccinated against it. Therefore, the typical intervention that your primary care doctor
will perform when you have an injury like this is revaccinate you against tetanus just to ensure that you stay protected and that the tetanus infection is prevented.
When you go to see your doctor, they will also be able to see if there is an local skin infection around the area where you stepped on the nail. If so, they will probably give you a course of oral antibiotics to help clear it up.
Get in to see your doctor right away!