Bear somehow able to swallow top of dog and bone (8,5)
'bone' is the definition.
(shoulder blade is a kind of bone)
'bear somehow able to swallow top of dog' is the wordplay.
'bear' becomes 'shoulder' (both can mean to carry or take responsibility for).
'somehow' is an anagram indicator.
'to swallow' is an insertion indicator.
'top of' says to take the initial letters.
The first letter of 'dog' is 'd'.
'able' is an anagram of 'blae'.
'blae' enclosing 'd' is 'blade'.
'and' acts as a link.
(Other definitions for shoulder blade that I've seen before include "Scapula", "bone", "joint?".)