We've got two five-year-old cats, full siblings from the same litter,
who have never lived apart... until the last few weeks.

The female came in one day with a broken leg (no other sign of injury --
we reckon she probably jumped short and fell out of a tree) and had to
be rushed off to have the leg set and bound up. We were told we had to
keep her in a cage for six weeks, and loaned a large contraption by the
vet.

The moment her brother set eyes on her with a bandaged leg inside this
cage in the kitchen, he hissed at her and refused to come into the house
at all, or even to eat from a bowl left on the back doorstep. After 24
hours we had to admit defeat and banish cat and cage out of sight
upstairs, since he's a wanderer who is quite capable of deciding to up
sticks and move elsewhere if his home is invaded by strange cat-monsters
from outer space...

As a result, he has had free reign over the entire territory, house and
garden, for six weeks, and shown no sign of missing his sister at all --
in the old days, they used to get worried when one or the other failed
to turn up, and go looking and calling.

This week the bandage finally came off, and the invalid was allowed out
of her cage, and after a day or so allowed to roam the entire house. But
every time they meet, her brother hisses or growls at her, backs away
and occasionally takes a swipe -- despite the fact that when they first
saw other, her reaction was to run towards him with a little chirrup of
greeting.

After several days' supervised time together, they now seem to be
capable of remaining in the same room, e.g. to feed, without active
signs of hostility, but whenever the female makes friendly overtures she
gets the same rude reaction. This evening, he walked past in the
corridor, carefully sniffed her rear, and *then* hissed -- having
apparently first made sure it was addressed to the right cat!

Any theories as to the psychology of what is going on, and how we can
'reintegrate' these two adult cats?