Breakdown of Если щиколотка болит, лучше посидеть дома и не идти на долгую прогулку.
Questions & Answers about Если щиколотка болит, лучше посидеть дома и не идти на долгую прогулку.
Both are possible.
- Если щиколотка болит = If the ankle hurts / If your ankle hurts
- Если у тебя болит щиколотка = If your ankle hurts
Russian often leaves out the possessor (my, your, his) when it is obvious from context, especially with body parts. So щиколотка болит sounds natural as a general statement or piece of advice.
Adding у тебя makes it more specifically about your ankle.
Because the subject is щиколотка, which is singular feminine.
- щиколотка болит = the ankle hurts
- ноги болят = the legs hurt
In Russian, the body part is often treated as the grammatical subject:
- Голова болит = My head hurts
- Рука болит = My arm hurts
So the verb agrees with щиколотка, not with an implied person.