Some work needed in joint (4)
I believe the answer is:
knee
'joint' is the definition.
(knee is a kind of joint)
'some work needed in' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'KNEE' can be found hidden inside 'work needed in'.
(Other definitions for knee that I've seen before include "Genuflector?" , "Joint of the body" , "Hinge between the thigh and the shin" , "One bent in genuflection" , "This is capped by the patella" .)