Bones of foot on broken stair (5)
I believe the answer is:
tarsi
'bones of foot' is the definition.
'tarsi' can be an answer for 'bones' (bones of the foot). I'm not certain of the 'of foot' bit.
'broken stair' is the wordplay.
'broken' indicates an anagram.
'stair' with letters rearranged gives 'TARSI'.
'on' is the link.
Can you help me to learn more?
(Other definitions for tarsi that I've seen before include "collections of bones?" , "Foot bones" , "Ankle bones" , "Parts of skeleton" , "parts of leg" .)