Actually, Zant isn't the one who injures Midna. The light spirit tries to attack Zant, but Zant surpresses the light spirit with his twilight, then curses Link. Then to show Midna that people in the normal world are the enemy, he undoes the Twilight, which reawakens the spirit, who continues it's attack, but now against Midna. Still there's a lot of manhandling and Link and Midna are severly outmatched.