There are several avenues that can be taken here....
"Heather Mills is serious about getting to work and making sure one of her legs doesn't wobble around and accidentally hits somebody in the audience."
When I have a wobbly leg, I generally put a matchbook under it to steady it
"Heather says has a spare leg in case her prosthetic limb breaks while she is performing "
Does she carry other spare bodyparts in case of a failure?, wear and tear?
"Heather, 39, the estranged wife of Paul McCartney, is reportedly already struggling after suffering blisters on her partly-amputated leg as a result of grueling training sessions."
Now here is where we can create stump pus jokes, I'm sure this will be a valuable source for jokes and mirthmaking.