Questo osso è rotto.

The sentence breaks down like this:

• Questo = this
• osso = bone
• è = is
• rotto = broken

So the structure is:

• demonstrative + noun + verb + adjective

In other words, questo osso is the subject, è is the verb, and rotto describes the condition of the bone.

Because osso is masculine singular, and questo has to agree with it.

The basic forms are:

• questo = masculine singular
• questa = feminine singular
• questi = masculine plural
• queste = feminine plural

So:

• questo osso = this bone
• questa gamba = this leg

Agreement is very important in Italian.

Because questo already works like this in English and normally takes the place of an article.

So Italian says:

• questo osso = this bone

not:

• il questo osso

That would be incorrect in standard Italian.

The accent is important because è and e are different words:

• è = is
• e = and

So the accent helps you distinguish them in writing.

It also reflects pronunciation: è is pronounced with an open e sound.

Because rotto has to agree with osso, which is masculine singular.

Compare:

• Questo osso è rotto = masculine singular
• Questa gamba è rotta = feminine singular
• Questi denti sono rotti = masculine plural
• Queste ossa sono rotte = feminine plural

So the ending changes depending on the noun it describes.

It is originally the past participle of rompere (to break), but here it is being used like an adjective.

So in this sentence, rotto describes the state of the bone: it is in a broken condition.

This is very common in Italian. Many past participles can function as adjectives:

• La porta è chiusa = The door is closed
• Il vetro è rotto = The glass is broken

Yes, you may also see quest'osso before a vowel.

Before singular nouns beginning with a vowel, questo/questa is often shortened to quest':

• quest'uomo
• quest'amica
• quest'osso

So quest'osso è rotto is also possible. If you are unsure, it is useful to recognize both forms.

A rough guide is:

KWEH-sto OS-so eh ROT-to

A few important points:

• questo starts with a kw sound: kweh-
• osso has a double s
• rotto has a double t
• è is pronounced like an open e

The doubled consonants matter in Italian, so osso and rotto should be pronounced more strongly than a single s or t.

Rotto is perfectly understandable and natural in everyday language.

However, for a bone, Italians may also use fratturato, which is more specific or medical:

• Questo osso è rotto = everyday, plain language
• Questo osso è fratturato = more medical/technical

So rotto is fine, but fratturato is more precise in a medical context.

This is a useful question because osso has an irregular plural pattern.

You may see:

• ossi
• ossa

Very roughly:

• ossa is often used for bones of the body collectively
• ossi is often used for individual bones or in other contexts

For many learners, the most useful form to recognize first is:

• le ossa = the bones

So:

• Queste ossa sono rotte = These bones are broken

This is a slightly advanced point, but it is worth knowing because osso does not behave like a completely regular noun.