Sailor’s useless ankle or heel bone (6)

I believe the answer is:

tarsus

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'bone' is the definition.
(I've seen this before)

'sailor's useless' is the wordplay.
'sailor's' becomes 'tar's' (term for a sailor).
'useless' becomes 'us' (abbreviation for unserviceable).
'tars'+'us'='TARSUS'

'ankle or heel' acts as a link.
This may not be correct. Some or all of it may be part of another bit of the clue.

Can you help me to learn more?

(Other definitions for tarsus that I've seen before include "Birthplace of St Paul" , "biblical city" , "Group of bones" , "ancient Turkish city" , "Arrangement of bones" .)

I've seen this clue in The Times.

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