Minimally restrictive interconnected bone structures (4)
I believe the answer is:
ribs
'minimally restrictive interconnected bone structures' is the definition.
'ribs' can be an answer for 'structures' (rib is a kind of structure). I'm not sure about the 'minimally restrictive interconnected bone' bit.
'bone structures' is the wordplay.
'bone' becomes 'rib' (rib is a kind of bone).
'structures' becomes 's' (this could be a standard abbreviation I've not previously seen).
'rib'+'s'='RIBS'
(Other definitions for ribs that I've seen before include "Arched bones extending from the spine" , "Teases (informal)" , "Curved bones around the chest" , "Is making fun of" , "Chest bones, tasty when spare" .)