Just watching Benidorm ER & a person trying to use a pair of Crutches, why don't they use a device similar to a Roller Skate / Small skateboard for the injured leg /foot?
So that the injured leg can hurtle off, out of control, until the good leg has equal damage to the hurt one.
Then you could use two roller skates.
Oh. Let me think a minute.....
Most hospital physio departments now have these TWR. I have used one several times following operations on my ankle when I couldn't use crutches because I had tendonitis in the other leg. Very good for getting around.
http://www.walk-aid.co.uk/