Ребро зламалося.

Because the subject ребро is neuter singular.

In the past tense, Ukrainian verbs agree with the subject in gender and number:

• masculine: -в
• feminine: -ла
• neuter: -ло
• plural: -ли

So:

• він зламався = he broke / it broke
• вона зламалася = she broke / it broke
• воно зламалося = it broke
• вони зламалися = they broke

Here, ребро is a neuter noun, so the verb is зламалося.

The final -ся is the reflexive particle, which in this sentence helps give the meaning broke / got broken rather than broke something.

The dictionary form is зламатися.

That is the infinitive.
You can break the form down like this:

• з- = prefix
• лам = root related to breaking
• а-ти = infinitive ending
• -ся = reflexive particle

So:

• зламатися = to break, to get broken
• зламалося = broke / got broken

Not literally.

In sentences like this, -ся often makes the verb intransitive or middle/reflexive-like, meaning that something undergoes the action rather than does it to something else.

Compare:

• Він зламав ребро. = He broke a rib.
• Ребро зламалося. = The rib broke.

So зламалося does not usually suggest that the rib intentionally did something to itself. It simply means that the rib ended up broken.

This is very similar to English pairs like:

• I broke the glass.
• The glass broke.

Because it is the subject of the sentence.

In Ребро зламалося, the rib is the thing that broke, so it is the grammatical subject. Subjects are normally in the nominative case in Ukrainian.

So:

• ребро = nominative singular
• зламалося = verb agreeing with that subject

Even though in English the meaning may feel a bit like was broken, Ukrainian still treats ребро as the subject of an intransitive/reflexive verb here.

This is a question of aspect.

• ламатися = imperfective
• зламатися = perfective

Very roughly:

• ламатися focuses on the process, repetition, or ongoing action
• зламатися focuses on the completed result

Examples:

• Ребро ламалося. = The rib was breaking / used to break / was in the process of breaking.
  This is much less natural in many contexts unless you really want to emphasize process.
• Ребро зламалося. = The rib broke.
  This is the normal way to say the event happened and was completed.

English speakers often find aspect tricky, but here the perfective зламатися is the natural choice for a single completed event.

Usually it is closer to The rib broke.

The sentence presents the event as something that happened to the rib, without directly naming an agent.

• Ребро зламалося. = The rib broke.
• Ребро було зламане. = The rib was broken.
  This sounds more like a passive result state.

So if you just want to say that the rib ended up broken as an event, зламалося is the more natural form.

Because Ukrainian has no articles.

So ребро can mean:

• a rib
• the rib

Which one is intended depends on context.

This is normal in Ukrainian. Learners have to get used to understanding definiteness from the situation rather than from separate words like a and the.

Yes. Ukrainian word order is fairly flexible, and changing it can shift focus or emphasis.

The neutral order here is:

• Ребро зламалося.

You could also hear:

• Зламалося ребро.

This can sound more like It was the rib that broke or put more focus on the event/result.

So the basic meaning stays similar, but word order can affect what sounds new, important, or emphasized.

The usual stress is:

• ребро́
• злама́лося

So the sentence is pronounced approximately:

reh-BROH zlah-MAH-lo-sya

A rougher sound guide for English speakers:

• ре = like re in report, but shorter
• бро́ = BROH
• зла = zla
• ма́ = stressed MAH
• лося = lo-sya

Stress matters in Ukrainian, so it is worth learning the stressed syllables with new words.

No. Ребро can also mean edge or ridge in some contexts, just as rib in English can have extended meanings.

However, in a sentence like Ребро зламалося, the anatomical meaning rib is very natural if that is the context you were given.

So learners should remember:

• ребро = rib
• but it may have broader meanings depending on context

A natural way is:

• Я зламав ребро. if the speaker is male
• Я зламала ребро. if the speaker is female

Very often Ukrainian also uses a possessive idea only when needed from context. So ребро can still mean my rib if the context already makes that clear.

If you want to be more explicit, you can say:

• Я зламав собі ребро.
• Я зламала собі ребро.

This literally means something like I broke a rib to myself, but idiomatically it means I broke my rib.

You simply add не before the verb:

• Ребро не зламалося. = The rib did not break.

This is the standard way to negate verbs in Ukrainian.

The simplest way is just to use question intonation:

• Ребро зламалося? = Did the rib break?

You can also add a question word if needed, for example:

• Коли ребро зламалося? = When did the rib break?
• Як ребро зламалося? = How did the rib break?

Ukrainian often relies on intonation rather than changing word order the way English does with did.