What kind of injuries might allow tetanus to enter the body?

Any broken skin: Tetanus spores require only access to an open wound (cut or puncture)to begin the process of growth and elaboration of the toxin of tetanus. The nastier and dirtier the wound, the more likely you are to find tetanus a factor. As long as the skin is not broken, concern is minimal.

Penetrating: Any injury where the skin is broken can allow the tetanus toxoid in the body. Most likely is an injury in an enviroment where animals have been present, but can occur anywhere.