Fresh hopes rest on son getting replacement arms perhaps (10)
I believe the answer is:
prostheses
'replacement arms perhaps' is the definition.
I can't judge whether this definition defines the answer.
'fresh hopes rest on son' is the wordplay.
'fresh' indicates anagramming the letters (a fresh re-ordering of the letters).
'on' means one lot of letters goes inside another (as in clothing 'on' a person).
'son' becomes 's' (genealogical abbreviation for son).
'hopes'+'rest'='hopesrest'
'hopesrest' with letters rearranged gives 'prosthees'.
'prosthees' enclosing 's' is 'PROSTHESES'.
'getting' acts as a link.
Can you help me to learn more?
(Another definition for prostheses that I've seen is " artificial parts".)