Hee is how Rainbow Dash hurts her wing in My Little Pony: Iron Mare.

(We see Cloudsdale)

(We zoom in)

(We see many Pegasi flying around)

(We then see Rainbow Dash relaxing)

(We then hear Soarin and Spitfire hauling supplies back to the academy]

Soarin: Steady. Steady.

(Suddenly, a wheel runs over a big lump causing the supplies to topple in Soarin's direction)

(Seeing this, Rainbow pushes him out of the way and the supplies fall on top of her wing)

Spitfire and Soarin: Rainbow!

(They rush her over to the hospital)

(Later, Rainbow wakes up in a hospital bed)

Twilight Sparkle: Rainbow, you're alright?

Rainbow Dash: