Twitch follows fractured tibia, on medication (10)
I believe the answer is:
antibiotic
'medication' is the definition.
(antibiotic is a kind of medication)
'twitch follows fractured tibia on' is the wordplay.
'twitch' becomes 'tic' (tic is a kind of twitch).
'follows' says to put letters next to each other.
'fractured' indicates anagramming the letters.
'tibia'+'on'='tibiaon'
'tibiaon' anagrammed gives 'antibio'.
'tic' after 'antibio' is 'ANTIBIOTIC'.
(Other definitions for antibiotic that I've seen before include "Medication" , "Remedy" , "Infection treatment" , "Medicine destroying micro-organisms" , "Substance that destroys bacteria" .)