If your father in law believe in alternative treatment may use magnetotherapy treatment;
1. Place south pole of med. power magnet touching knee for half an hour twice a day for one month.
with mustered oil charged with south pole,twice a day regularly.
3. Drink water charged with med. power magnet ,both poles ,4 time a day regularly
hope get releif from pain.
repot after one month.
note ;- feel free to contact for detail n magnets if required.