In inguinal hernia repair surgery, does injury to the cremaster muscle/s usually occurs?

Not injury...: The cremasteric fibers that run along the spermatic cord are occasionally divided to gain better access to the hernia sac and allow a better hernia repair. Sometimes, the sac is adherent to the cord structures, also requiring division of the cremasterics, which is generally of little clinical consequence.

Yes, because: It is inherent part of surgery, especially if it is indirect type of inguinal hernia. Cremaster muscle injury usually is of little if any clinical significance. Ask your surgeon to explain to you with a diagram, because it is difficult to explain without drawing a picture.