Leading surgeon maps out muscular contraction (5)
I believe the answer is:
spasm
'muscular contraction' is the definition.
(I've seen this before)
'leading surgeon maps out' is the wordplay.
'leading' says to take the initial letters.
'out' indicates an anagram (out can mean wrong or inaccurate).
The first letter of 'surgeon' is 's'.
'maps' is an anagram of 'pasm'.
's'+'pasm'='SPASM'
(Other definitions for spasm that I've seen before include "Sudden involuntary contraction of a muscle" , "Tic, sudden contraction" , "Involuntary muscular contraction" , "cramp" , "Fit" .)