Ŝi etendos la kubuton, krom se la tendeno doloros.

The ending -os marks the future tense in Esperanto.

• etendos = will extend
• doloros = will hurt / will be painful

Esperanto verb endings are very regular:

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

So this sentence is talking about something that will happen in the future.

The -n marks the direct object.

In Ŝi etendos la kubuton:

• Ŝi = she, the subject
• etendos = will extend
• la kubuton = the elbow, the thing being extended

So kubuto becomes kubuton because it receives the action.

This -n ending is one of the most important parts of Esperanto grammar.

Esperanto often uses the definite article with body parts when the owner is already clear from context.

So Ŝi etendos la kubuton naturally means She will extend her elbow, not some random elbow.

This is similar to how some other languages handle body parts. In English, we often prefer her elbow, but in Esperanto la kubuton is very normal when the possessor is obvious.

You could say ŝian kubuton, but it is often unnecessary unless you want to emphasize ownership.

Krom se means unless.

Literally, it is something like except if:

• krom = apart from / except
• se = if

So:

• Ŝi etendos la kubuton, krom se la tendeno doloros.
• She will extend the elbow, unless the tendon hurts.

This is a very common and useful expression in Esperanto.

That is a very good question, because Esperanto and English handle this differently.

In Esperanto, if the meaning is future, it is very normal to use the future tense in both parts:

• Ŝi etendos...
• ...krom se la tendeno doloros.

In English, subordinate clauses after if, when, unless, and similar words often use the present tense even when the meaning is future:

• unless the tendon hurts

So the Esperanto future doloros is correct and natural here, even though English would usually not say will hurt.

Yes. Dolori means to hurt / to be painful.

So la tendeno doloros means:

• the tendon will hurt
• the tendon will be painful

This is a normal Esperanto pattern. The painful body part can be the subject.

Compare:

• Mia kapo doloras. = My head hurts.
• La genuo doloras. = The knee hurts.

So la tendeno doloros is perfectly natural.

The article la often appears when the speaker means a specific, identifiable thing.

Here, la tendeno probably refers to the relevant tendon connected with that elbow in the situation being discussed. Even if it has not been mentioned before, it can still be understood as a specific tendon known from context.

Without la, tendeno would sound more general, like a tendon.

So la tendeno fits the idea of a particular tendon that matters in this situation.

Yes. Esperanto word order is fairly flexible, especially because the -n ending helps show what is the object.

You could also say:

• Krom se la tendeno doloros, ŝi etendos la kubuton.

That means the same thing: Unless the tendon hurts, she will extend the elbow.

The original version puts the main action first. The reordered version puts the condition first. Both are grammatical.

The base form is etendi, which means to extend or to stretch out.

Here it is used transitively: someone extends something.

• etendi la brakon = extend the arm
• etendi la kubuton = extend the elbow

Strictly speaking, in English people often say extend the arm rather than extend the elbow, but Esperanto can express the joint movement this way, especially in a medical or physical-exercise context.

It sounds somewhat medical, instructional, or physical-therapy-related, mainly because of words like:

• kubuto = elbow
• tendeno = tendon
• etendi = extend

In ordinary conversation, people might choose simpler phrasing depending on the situation. But grammatically, the sentence is completely normal Esperanto.

It would fit well in contexts like:

• exercise instructions
• rehabilitation advice
• anatomy explanations
• medical descriptions