I got one of those from Coppull(actually,i usually get one EVERY time i go to Coppull).The cure is:
1) Hobble around for 3 weeks muttering about 'never hurting this much BITD'
2) Keep children,animals and Dwarves away from the knee.
3) Buy a pair of race pants and watch as the next time you fall off,they shred at the knee and it costs you £40(but no blood).
Hope it works