The most common and most likely answer to this crossword clue is the 7 letter word CENTRUM
C
E
N
T
R
U
M
More clues leading to the result CENTRUM
Buddy explains!

The straight part
We know that "acts as the back bone" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case acts as the back bone = centrum.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CENTRUM mean?
CENTRUM noun- A center.
- The central body of a vertebra; the solid piece to which the arches and some other parts are or may be attached.
- The basis or fundamental portion of one of the cranial segments, regarded as analogous to vertebrae.
- The focus or place of origin of an earthquake.