Joint nurse rolled that Keef regularly inhales (4)
I believe the answer is:
knee
'joint nurse' is the definition.
'knee' can be an answer for 'joint' (I've seen this in another clue). I'm not certain of the 'nurse' bit.
'rolled that keef regularly inhales' is the wordplay.
'rolled' says the letters should be written in reverse (letters roll back).
'that' becomes 'en' (I can't explain this - if you can you should give a lot more credence to this answer).
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'inhales' is an insertion indicator (inserted letters are inhaled).
The alternate letters of 'keef' are 'ke'.
'en' backwards is 'ne'.
'ne' going inside 'ke' is 'KNEE'.
Can you help me to learn more?
(Other definitions for knee that I've seen before include "for going on begging" , "Leg bender" , "Hinge joint" , "Where the femur meets the tibia" , "Technical name for this joint is genu" .)