Likely to go mad, being in need of a joint? (8)
I believe the answer is:
unhinged
I believe this clue is a double definition.
'likely to go mad' is the first definition.
(unhinged can mean mentally unstable)
'in need of a joint?' is the second definition.
(something without a hinge)
'being' is the link.
(Other definitions for unhinged that I've seen before include "Mad - hen dug in (anag)" , "Wild" , "[NUTTY]" , "Bats" , "End I hung out to be mentally unbalanced" .)