La kuracisto klarigas la diagnozon de la artiko.

The -n ending marks the direct object in Esperanto.

In La kuracisto klarigas la diagnozon de la artiko:

• La kuracisto = the doctor → the subject, the one doing the action
• klarigas = explains
• la diagnozon = the diagnosis → the thing being explained

So diagnozo becomes diagnozon because it is receiving the action of explains.

This -n ending is called the accusative ending.

Because kuracisto is the subject, not the direct object.

Esperanto usually marks:

• subject: no -n
• direct object: -n

So:

• La kuracisto = the doctor does the explaining
• la diagnozon = the diagnosis is what gets explained

Even if the word order changed, the -n would still help show what role the noun has.

Kuracisto means doctor.

It can be broken down like this:

• kuraci = to treat medically, to cure
• -ist- = a person professionally associated with something
• -o = noun ending

So kuracisto is literally something like a medical practitioner or someone who treats.

This is very typical Esperanto word-building.

Klarigas means explains.

It comes from:

• klara = clear
• klarigi = to make clear, to explain
• -as = present tense

So klarigas means is explaining or explains.

In Esperanto verb endings are very regular:

• -as = present
• -is = past
• -os = future
• -us = conditional
• -u = command / jussive
• -i = infinitive

So klarigas is simply the present-tense form.

Because klaras and klarigas mean different things.

• klara = clear
• klaras = is clear
• klarigi = to make clear, to explain
• klarigas = explains / makes clear

So:

• La diagnozo klaras = The diagnosis is clear.
• La kuracisto klarigas la diagnozon = The doctor explains the diagnosis.

The suffix -ig- often means to cause or make something become something.

So klarigi literally means to make clear.

De la artiko means of the joint.

The preposition de often shows a relationship like:

• possession
• origin
• source
• association
• “of” in a broad sense

Here la diagnozo de la artiko means the diagnosis of the joint, or more naturally in English, the diagnosis concerning the joint.

So the phrase tells us what the diagnosis is about.

Because la is the Esperanto word for the, and it does not change form.

So:

• la kuracisto = the doctor
• la diagnozon = the diagnosis
• la artiko = the joint

Unlike English, Esperanto has only one definite article: la.

It does not change for:

• gender
• number
• case

Even when the noun gets -n, the article stays la:

• la diagnozo
• la diagnozon

No. Esperanto has no indefinite article.

So:

• kuracisto can mean a doctor or just doctor, depending on context
• la kuracisto specifically means the doctor

In your sentence, la kuracisto refers to a specific doctor, and la artiko refers to a specific joint.

Yes, Esperanto word order is fairly flexible, because endings help show grammatical roles.

For example, these would still be understandable:

• La kuracisto klarigas la diagnozon de la artiko.
• La diagnozon de la artiko klarigas la kuracisto.

Because diagnozon has -n, it remains the object.

That said, the most neutral and common order is subject–verb–object, which is exactly what your sentence uses.

Because de usually attaches naturally to the noun phrase before it here.

So:

• la diagnozon de la artiko = the diagnosis of the joint

That whole chunk acts as the object of klarigas.

It would be strange to understand klarigas de la artiko as a unit, because klarigi does not normally take de in that way.

So the structure is:

• La kuracisto = subject
• klarigas = verb
• la diagnozon de la artiko = object phrase

Yes. Literal of the joint is fine for understanding the grammar, but English may prefer something a little more natural depending on context, such as:

• the diagnosis of the joint
• the joint’s diagnosis
• the diagnosis concerning the joint
• the diagnosis related to the joint

Esperanto de is often broader than English of, so the best English wording depends on what meaning is intended.

A helpful approximation is:

lah koo-ra-TSIS-toh kla-REE-gahs lah dee-ag-NOH-zohn deh lah ar-TEE-koh

A few useful points:

• c is always like ts
• g is always hard, as in go
• z is like English z
• stress is usually on the second-to-last syllable

So:

• kuracisto → ku-ra-CIS-to
• klarigas → kla-RI-gas
• diagnozon → di-ag-NO-zon
• artiko → ar-TI-ko

The main endings to notice are:

• -o = noun
• -on = noun + accusative
• -as = present-tense verb

In this sentence:

• kuracist-o = doctor
• diagnoz-o-n = diagnosis + object marker
• artik-o = joint
• klarig-as = explains

This regular system is one of the biggest advantages of Esperanto: once you know the endings, sentence structure becomes much easier to read.