Il medico controlla l'osso.

Because medico begins with m, and masculine singular nouns normally take il before most consonants:

• il medico
• il libro
• il ragazzo

You use lo before certain sounds, such as z, s + consonant, gn, ps, x, and y:

• lo studente
• lo zio
• lo psicologo

So il medico is the correct form.

The apostrophe shows elision: the final vowel of the article is dropped before a word beginning with a vowel.

Here, the full article would be lo, but before osso it becomes l':

• lo osso → l'osso

This is standard in Italian with singular articles before vowels:

• l'amico
• l'uomo
• l'osso

So l'osso means the bone.

Because osso is one of those masculine nouns that take lo in the singular when not elided.

You can see this clearly in the plural:

• singular: l'osso
• plural: le ossa when referring to bones of the skeleton in a collective sense, but gli ossi can also exist in other contexts

For the singular article, the key point is that the underlying form is lo, which becomes l' before a vowel.

So the pattern is:

• lo
  • vowel-starting masculine noun → l'

Controlla is in the present tense, third person singular, from the verb controllare.

That means it can mean:

• he checks
• she checks
• it checks
• or, depending on context, is checking

In this sentence, il medico controlla l'osso, the subject is the doctor, so controlla means the doctor checks / is checking.

Because the subject is il medico, which is third person singular: the doctor.

The verb controllare is conjugated like this in the present:

• io controllo = I check
• tu controlli = you check
• lui/lei controlla = he/she checks
• noi controlliamo = we check
• voi controllate = you all check
• loro controllano = they check

Since il medico is a singular he/she type subject grammatically, Italian uses controlla.

Not necessarily in every context, but grammatically il medico is masculine singular.

Italian often uses masculine forms as dictionary forms or default forms for professions. A female doctor can also be called il medico in some usage, especially in more formal or traditional contexts. However, you may also hear feminine forms such as:

• la medica
• sometimes la dottoressa, depending on context and nuance

For this sentence alone, il medico is grammatically masculine because of il.

Yes, but Italian is somewhat flexible.

The basic order in this sentence is:

subject + verb + object

• Il medico = subject
• controlla = verb
• l'osso = direct object

This is the most neutral and natural order in many contexts.

Italian can sometimes change word order for emphasis, for example:

• L'osso lo controlla il medico

But that is more marked and context-dependent. For a simple statement, Il medico controlla l'osso is the normal order.

You know mainly from the structure and meaning of the sentence.

In Il medico controlla l'osso:

• Il medico comes before the verb in the normal subject position
• l'osso comes after the verb in the normal object position

Also, semantically, it makes sense that the doctor checks the bone, not that the bone checks the doctor.

Italian does not rely as heavily on word endings for subject/object distinction as some other languages, so word order and context are very important.

Yes. Controllare can have several related meanings depending on context, such as:

• to check
• to examine
• to inspect
• sometimes to control in certain contexts

In a medical sentence like this, checks or examines is the most natural meaning.

So Il medico controlla l'osso could be understood as The doctor checks/examines the bone.

It is pronounced roughly like LOSS-so, with the l linked directly to the next word because of the elision.

A few useful points:

• the o in osso is a clear vowel sound
• the ss is pronounced as a strong doubled consonant in Italian
• the apostrophe does not create a pause; it just shows that the vowel of the article has dropped

So you should say it smoothly, almost as one unit: l'osso.

Because Italian does not need an auxiliary like is to form a basic present-tense sentence here.

English often distinguishes:

• The doctor checks
• The doctor is checking

Italian simple present, controlla, can cover both ideas depending on context.

So Il medico controlla l'osso is a complete sentence without any extra word for is.

Yes, Italian often drops subject pronouns, but nouns are usually kept when you want to state who is doing the action.

• Controlla l'osso by itself means He/She checks the bone or is checking the bone, depending on context.
• Il medico controlla l'osso explicitly says that the doctor is the one doing it.

So omitting the subject is possible only if the subject is already understood from context.