Some luck needed in joint (4)
I believe the answer is:
knee
'joint' is the definition.
(I know that knee is a type of ginglymus)
'some luck needed in' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'KNEE' can be found hidden inside 'luck needed in'.
(Other definitions for knee that I've seen before include "Genuflector?" , "middle part of leg" , "Leg hinge" , "It jerks reactively" , "This is capped by the patella" .)