Ring-shaped structures in ulna damage (6)

I believe the answer is:

annuli

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'ring-shaped structures' is the definition.
Although both the answer and definition are plural nouns, I can't see how they can define each other.

'in ulna damage' is the wordplay.
'damage' indicates an anagram (I've seen 'damaged' mean this).
'in'+'ulna'='inulna'
'inulna' is an anagram of 'ANNULI'.

Can you help me to learn more?

(Other definitions for annuli that I've seen before include "round these parts" , "Ring-shaped objects" , "Areas between two concentric circles" .)

I've seen this clue in the Sydney Morning Herald.

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