W stawie jest obrzęk.

Because w meaning in takes the locative case when it describes location.

• basic form: staw = joint
• after w for location: w stawie = in the joint

So this is a normal case change:

• staw → w stawie

If w means movement into something, it can take the accusative in other contexts, but here it means static location, so locative is used.

Stawie is locative singular.

The dictionary form is staw. Its singular cases include:

• nominative: staw
• genitive: stawu
• dative: stawowi
• accusative: staw
• instrumental: stawem
• locative: stawie
• vocative: stawie

After w meaning in, Polish uses the locative, so we get w stawie.

Jest is the 3rd person singular form of być = to be.

Here it works like there is / is in English:

• W stawie jest obrzęk. = There is swelling in the joint.

Polish often uses jest in this kind of sentence to state that something exists or is present somewhere.

You may sometimes see the verb omitted in very short notes or headlines, especially in medical writing, but in a normal full sentence jest is the standard form.

Because obrzęk is the grammatical subject of the sentence.

In a sentence like:

• W stawie jest obrzęk

the thing that is present is obrzęk, so it appears in the nominative singular.

This is similar to English existential sentences:

• There is swelling in the joint.

Even though English starts with there, the real thing being talked about is swelling. In Polish, that noun is normally in the nominative:

• obrzęk

Obrzęk is a masculine inanimate noun.

That matters because it affects agreement in other contexts. For example:

• ten obrzęk = this swelling
• duży obrzęk = a large swelling

In your sentence, it goes with:

• jest because it is singular

Polish does not have articles like English a/an and the.

So:

• staw can mean a joint or the joint
• obrzęk can mean swelling or the swelling, depending on context

In W stawie jest obrzęk, English usually needs an article or some restructuring, but Polish does not.

The exact English translation depends on context:

• There is swelling in the joint
• The joint has swelling
• There is a swelling in the joint

Yes, Polish word order is more flexible than English, but different orders can sound more or less natural depending on emphasis.

Your sentence:

• W stawie jest obrzęk.

This is a very natural way to present new information: in the joint, there is swelling.

Other possible orders include:

• Obrzęk jest w stawie.
• Jest obrzęk w stawie.

These are grammatically possible, but they may sound more marked or shift the emphasis.

A rough idea:

• W stawie jest obrzęk → neutral, natural
• Obrzęk jest w stawie → emphasizes obrzęk
• Jest obrzęk w stawie → possible, but less standard in many contexts

No. Staw can also mean pond.

So by itself, w stawie could mean:

• in the joint
• in the pond

But the context makes the meaning clear. With obrzęk meaning swelling, the medical meaning is the obvious one:

• W stawie jest obrzęk. = There is swelling in the joint.

A pond cannot realistically have obrzęk, so there is no real confusion here.

In careful spelling-based pronunciation, w is normally like English v.

But in actual Polish pronunciation, w often changes its voicing depending on the next sound. Before the voiceless s in stawie, many speakers pronounce it more like f.

So w stawie is often pronounced approximately like:

• f STA-vye

This is a normal sound change in Polish and does not affect spelling.

A simple learner-friendly guide:

• stawie ≈ STAH-vye
• obrzęk ≈ OB-zhengk or OB-zhenk depending on how precisely you render the nasal vowel

A few useful points:

• w is like English v
• ie after a consonant often sounds roughly like ye
• rz usually sounds like the zh in measure
• ę is a nasal vowel; before k it is often heard approximately as en/em plus the consonant

Stress in Polish is usually on the second-to-last syllable:

• STA-wie
• OB-rzęk

Yes, but the meaning changes.

• W stawie jest obrzęk. = There is swelling in the joint.
• W stawie są obrzęki. = There are swellings in the joint.

The singular obrzęk usually refers to the condition of swelling in a general or medical sense. The plural obrzęki would suggest multiple separate swellings, which is less likely in this exact medical phrasing.

So for a general statement about swelling being present, jest obrzęk is the more natural choice.

Yes, it sounds natural and medically standard.

Polish often uses this pattern:

• W + location + jest + noun

For example:

• W nodze jest ból. = There is pain in the leg.
• W płucu jest zmiana. = There is a lesion/change in the lung.
• W stawie jest obrzęk. = There is swelling in the joint.

It is a straightforward way to describe a finding or symptom.

Not exactly with the same meaning, and usually not in standard medical wording.

• W stawie jest obrzęk means There is swelling in the joint
• Staw jest obrzęknięty would mean The joint is swollen

Those are closely related in meaning, but they are not structured the same way.

Also, in careful medical Polish, you are more likely to hear:

• Staw jest obrzękły or
• Występuje obrzęk stawu or
• W stawie jest obrzęk

So your original sentence is a very normal noun-based medical description.