Sendi lutut Kakek sakit.

Sendi means joint, and lutut means knee. Together, sendi lutut means knee joint.

This is a common Indonesian noun pattern:

• sendi = joint
• lutut = knee
• sendi lutut = knee joint

The first noun is the main thing, and the second noun specifies what kind of thing it is.

Because Indonesian usually puts the possessor after the thing possessed.

So:

• lutut Kakek = Grandpa's knee
• sendi lutut Kakek = Grandpa's knee joint

This is very different from English, which often uses 's before the possessed noun.

Compare:

• English: Grandpa's knee
• Indonesian: lutut Kakek

Indonesian often leaves out the verb to be in simple statements.

So:

• Sendi lutut Kakek sakit literally looks like Grandpa's knee joint painful
• But it naturally means Grandpa's knee joint hurts or Grandpa's knee joint is painful

You do not normally need a word like is here.

Here, sakit means hurts, is painful, or is sore.

The word sakit can mean slightly different things depending on what it describes:

• Kakek sakit = Grandpa is sick/ill
• Lutut Kakek sakit = Grandpa's knee hurts
• Sendi lutut Kakek sakit = Grandpa's knee joint hurts

So with a body part, sakit usually means painful rather than ill.

For learners, it is easiest to think of sakit here as a stative word that works like painful / hurting.

Indonesian does not always divide words into parts of speech in exactly the same way English does. In this sentence, sakit is the predicate, so it functions like:

• is painful
• hurts

So even if a dictionary lists it as an adjective, in actual sentences it can behave a lot like a verb in English translation.

Because kinship terms in Indonesian are often capitalized when they are used like a name or a title.

So:

• kakek = grandfather, an old man, grandpa in a general sense
• Kakek = Grandpa, referring to a specific person respectfully

This is similar to English:

• my grandfather
• Grandpa

If it is just a common noun, lowercase is more normal. If it is used like a form of address or a family title, capitalization is common.

Yes, it is grammatical and understandable, but sendi lutut sounds a bit more anatomical or specific than everyday speech.

In casual conversation, people might more often say:

• Lutut Kakek sakit. = Grandpa's knee hurts.

Using sendi lutut emphasizes that the pain is in the joint, not just the knee area in general.

By itself, it does not clearly say.

Indonesian nouns usually do not mark singular vs. plural unless needed. So the sentence just tells you that Grandpa's knee joint hurts, and context decides the rest.

If you want to be more specific, you could say:

• sendi lutut kiri Kakek = Grandpa's left knee joint
• sendi lutut kanan Kakek = Grandpa's right knee joint
• kedua sendi lutut Kakek = both of Grandpa's knee joints

It depends on context.

Indonesian often leaves out words like my, the, and a when they are understood from the situation. So Kakek could be understood as:

• Grandpa
• my grandpa
• the grandfather

In family context, Kakek often naturally means Grandpa.

No, not in this sentence.

The subject is sendi lutut Kakek = Grandpa's knee joint, and sakit describes that whole noun phrase.

So the meaning is:

• Grandpa's knee joint hurts

If you wanted to say Grandpa is sick, you would say:

• Kakek sakit.