For all of us who work with human beings, our humility brings us always back to: First, do no harm. Sometimes that's hard. Sometimes we make mistakes, notice things we wish we'd known before, or had been able to handle or perform better.
Don't insist a student take a pose s/he doesn't want to do. Don't ask twice. Respect your students' body wisdom. Become unattached to that teacher/student hierarchy. Teach your students to trust themselves. That's how they'll make friends with their bodies. That's how they'll heal.
Yoga teachers can go a long way toward taking care of their students by avoiding triggering traumatic responses in those students have traumatic injuries. And you should, as part of responsible, ethical teaching practice.
The environment of the yoga class is particularly ripe for trauma triggering because of its inherently intimate nature, arising out of the integration of mind and body and the teacher's position as a leader and spiritual or physical authority, and the fact that trauma can be held in the body.