The most common and most likely answer to this crossword clue is the 7 letter word KNUCKLE
I've seen this crossword clue in Financial Times
K
N
U
C
K
L
E
Buddy explains!

The straight part
We know that "joint" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case joint = knuckle.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does KNUCKLE mean?
KNUCKLE noun- Any of the joints between the phalanges of the fingers.
- (by extension) A mechanical joint.
- A cut of meat.
- The curved part of the cushion at the entrance to the pockets on a cue sports table.
- The kneejoint of a quadruped, especially of a calf; formerly used of the kneejoint of a human being.
- The joint of a plant.
- A convex portion of a vessel's figure where a sudden change of shape occurs, as in a canal boat, where a nearly vertical side joins a nearly flat bottom.
- A contrivance, usually of brass or iron, and furnished with points, worn to protect the hand, to add force to a blow, and to disfigure the person struck; a knuckle duster.
- The rounded point where a flat changes to a slope on a piste.
- To apply pressure, or rub or massage with one's knuckles.
- To bend the fingers.
- To touch one's forehead as a mark of respect.
- To yield.