Upset at repetitive strain injury in ankle bones (5)
I believe the answer is:
tarsi
'ankle bones' is the definition.
(I've seen this before)
'upset at repetitive strain injury' is the wordplay.
'upset' says the letters should be written backwards.
'repetitive strain injury' becomes 'rsi' (this might be a standard abbreviation which I don't know about).
'at' reversed gives 'ta'.
'ta'+'rsi'='TARSI'
'in' is the link.
Can you help me to learn more?
(Other definitions for tarsi that I've seen before include "Bones of the ankles and heels" , "Parts of skeleton" , "collections of bones?" , "parts of leg" , "Foot bones" .)