The most common and most likely answer to this crossword clue is the 1 letter word R
R
More clues leading to the result R
- State of old thoroughfare more manageable, so some say
- Aye!
- Cardinal’s misinformation swallowed by wealthy target of Brexit?
- I DJ and I am in pub getting over arthritis treatment
- Agatha Christie’s distinct characters assembled in government building
- R
- 24 ORPINE/VICTIM
- Regularly in day they replace English with bull, ultimately
- Dish seen when hobbits and orcs get together in retirement
- Sweetheart, in essence, reveals vulgar quality
Buddy explains!

The straight part
We know that "arthritis treatment" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case arthritis treatment = r.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.