У мене болить зап’ястя.

This is a very common Ukrainian pattern.

With pain, sensations, and many physical states, Ukrainian often says:

У/В + person + болить/болять + body part

So У мене болить зап’ястя is literally something like At me, the wrist hurts, but naturally it means My wrist hurts.

Using я here would not sound natural.

Мене is the genitive form of я.

The preposition у (or в) requires that form in this construction:

• я = I
• мене = me / of me / at me, depending on the structure

So in У мене болить зап’ястя, мене is there because Ukrainian expresses this idea with у + genitive.

Because the verb agrees with зап’ястя, not with мене.

The thing that hurts is зап’ястя = wrist, and it is singular, so the verb is singular too:

• болить = hurts / is hurting

If more than one thing hurt, you would normally use болять:

• У мене болять руки = My arms hurt

Here зап’ястя is in the nominative singular because it is the grammatical subject of the sentence — the thing that is hurting.

So the structure is basically:

• У мене = for me / at me
• болить = hurts
• зап’ястя = the wrist

Even if the English sentence feels like my wrist is a possessed object, Ukrainian treats the wrist as the subject of болить.

Because У мене already makes that clear.

In Ukrainian, body parts are very often expressed without a possessive adjective when the owner is obvious:

• У мене болить голова = My head hurts
• У мене болить рука = My arm hurts
• У мене болить зап’ястя = My wrist hurts

You can add моє for emphasis, but it usually is not needed:

• У мене болить моє зап’ястя — grammatical, but usually unnecessary
• Моє зап’ястя болить — possible, but more emphatic or contrastive

Yes. У and в often alternate in Ukrainian for smoother pronunciation.

So both are natural:

• У мене болить зап’ястя
• В мене болить зап’ястя

The meaning is the same. The choice often depends on sound and flow.

A rough English-friendly pronunciation is za-PYAS-tya, with the stress on я.

The apostrophe in зап’ястя is important. It shows that the consonant before it is not softened, and that я is pronounced more like ya.

So it is not pronounced as one soft blended sound after п; instead, the apostrophe keeps a clearer break before я.

Also useful stress patterns for the whole sentence are:

• мене́
• боли́ть
• зап’я́стя

Yes. Ukrainian word order is more flexible than English word order because the grammar is shown by endings and structure, not only by position.

The most neutral version is:

У мене болить зап’ястя.

But other orders are possible for emphasis, such as:

• Зап’ястя у мене болить.
• У мене зап’ястя болить.

These can sound more marked or conversational. For a learner, У мене болить зап’ястя is the best standard pattern to remember.