Endlessly lucky Ken rolled joint (7)
I believe the answer is:
knuckle
'joint' is the definition.
(joint in the hand)
'endlessly lucky ken rolled' is the wordplay.
'endlessly' means to remove the last letter.
'rolled' is an anagram indicator.
'lucky' with its last letter taken off is 'luck'.
'luck'+'ken'='luckken'
'luckken' with letters rearranged gives 'KNUCKLE'.
(Other definitions for knuckle that I've seen before include "Joint (of veal or pork?)" , "& 22 Down Yield to pressure" , "A finger-joint" , "Part of the finger" , "Bunch of fives" .)