Without Leo's modified boilersuits, you'd get swelling in joints (8)
I believe the answer is:
bursitis
'swelling in joints' is the definition.
The definition and answer can be both states of affairs as well as being singular nouns.
Maybe there's a link between them I don't understand?
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for bursitis that I've seen before include "Condition such as housemaid's knee" , "Inflammation of a shoulder joint" .)