Joint operation in and on work posting (3,11)
I believe the answer is:
hip replacement
'joint operation' is the definition.
(operation to replace a joint)
'in and on work posting' is the wordplay.
'in' becomes 'hip' (both can mean fashionable).
'and' means one lot of letters go next to another.
'on' becomes 're' ('on' can be mean 'with reference to').
'work posting' becomes 'placement' (placement can mean a job posting).
'hip'+'re'+'placement'='HIP REPLACEMENT'
(Other definitions for hip replacement that I've seen before include "Joint operation" , "Inserted joint" .)