Point to plain disorder of the backbone (6)
I believe the answer is:
spinal
'of the backbone' is the definition.
(I've seen this before)
'point to plain disorder' is the wordplay.
'point' becomes 's' (South).
'to' means one lot of letters go next to another.
'disorder' is an anagram indicator (a disordered version of the letters).
'plain' anagrammed gives 'pinal'.
's'+'pinal'='SPINAL'
(Other definitions for spinal that I've seen before include "affecting the back?" , "of a vital column" , "Of the vertebrae" , "Member of dock family with edible stems" , "Type of column" .)