Lying with a bend in the backbone (6)
I believe the answer is:
supine
'lying' is the definition.
(I've seen this before)
'a bend in the backbone' is the wordplay.
'a bend' becomes 'u' (a U-bend is a kind of bend - pipe under sink).
'in' indicates putting letters inside.
'the backbone' becomes 'spine' ('spine' can be a synonym of 'backbone').
'u' put inside 'spine' is 'SUPINE'.
'with' acts as a link.
(Other definitions for supine that I've seen before include "Unresisting" , "Inert; on one's back" , "Lying face upwards, indolent" , "Laid-back" , "Flat on one's back" .)