Special dressing helps to heal broken bones (6)
I believe the answer is:
splint
'bones' is the definition.
(splint bone is a kind of bone)
'special dressing' is the wordplay.
'special' becomes 'sp' (abbreviation).
'dressing' becomes 'lint' (material used for dressing wounds).
'sp'+'lint'='SPLINT'
'helps to heal broken' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for splint that I've seen before include "Support for injured arm" , "Contrivance for holding a broken bone in position" , "Brace for broken limb" , "Stick or straight object to which broken limb is fastened" , "Bone setting support" .)