The most common and most likely answer to this crossword clue is the 10 letter word BOW-LEGGED
I've seen this crossword clue in The Guardian
B
O
W
-
L
E
G
G
E
D
Buddy explains!

The straight part
We know that "with mild deformity" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case with mild deformity = bow-legged.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.
Crossword Answer definitions
BOW-LEGGED adjective- Having a bowleg