English to Spanish Medical Medical: Instruments

Hola, necesito ayuda para entender esta frase:

"With traditional dilators that do not have directional functionality, how does the surgeon determine if their dilator is posterior or anterior to the nerve? What is the danger being posterior to the nerve?
They can’t. If a surgeon were posterior to the nerve and retracts anteriorly, they will stretch and damage the nerve."

¡Gracias!