Der Arzt verbindet meinen Daumen, und mein Ellbogen fühlt sich schon besser an.

That is a very common question. Verbinden has more than one meaning.

Here it means to bandage or to dress a wound. In a medical context, ein Körperteil verbinden means to wrap or bandage that body part.

So:

• Der Arzt verbindet meinen Daumen = The doctor is bandaging my thumb

In other contexts, verbinden can also mean:

• to connect
• to join
• to link

German often uses the same verb for several related ideas, and the context tells you which meaning is intended.

Because meinen Daumen is in the accusative case.

In the first clause, Der Arzt is the subject, and meinen Daumen is the direct object — it is the thing the doctor is treating.

The masculine possessive adjective mein changes in the accusative:

• nominative masculine: mein Daumen
• accusative masculine: meinen Daumen

So:

• mein Daumen = my thumb as the subject
• meinen Daumen = my thumb as the direct object

That is why the ending becomes -en.

Because in the second clause, mein Ellbogen is the subject, not the object.

The structure is:

• mein Ellbogen = subject
• fühlt sich ... an = verb

So Ellbogen is in the nominative case, and the masculine possessive form is:

• mein Ellbogen

If it were a direct object, then you would expect:

• meinen Ellbogen

Compare:

• Mein Ellbogen tut weh. = My elbow hurts.
• Der Arzt untersucht meinen Ellbogen. = The doctor examines my elbow.

This is the verb sich anfühlen, which means to feel in the sense of to seem / to feel a certain way.

Its basic form is:

• sich anfühlen = to feel

It is:

1. reflexive: it uses sich
2. separable: the prefix an- moves to the end in a main clause

So:

• infinitive: sich anfühlen
• main clause: fühlt sich ... an

That is why the sentence looks split up:

• mein Ellbogen fühlt sich schon besser an

Literally, it is something like:

• my elbow feels itself already better on

But natural English is:

• my elbow already feels better

Not really. In this verb, sich is just part of the standard structure.

Some German verbs are reflexive even when English does not use a reflexive form. Sich anfühlen is one of them.

So you simply learn it as:

• etwas fühlt sich gut/schlecht/besser an
• something feels good/bad/better

Examples:

• Das fühlt sich gut an. = That feels good.
• Meine Hand fühlt sich taub an. = My hand feels numb.

So sich here is grammatical, not especially literal.

Here schon means already.

So:

• mein Ellbogen fühlt sich schon besser an = my elbow already feels better

It suggests an improvement has begun.

Depending on tone and context, schon can have other meanings in German, but in this sentence already is the natural meaning.

Because anfühlen is a separable verb.

Many German verbs have a prefix that separates in main clauses. In this case:

• full infinitive: sich anfühlen
• present tense main clause: fühlt sich ... an

So the conjugated part goes in the normal verb position, and the prefix goes to the end.

Compare:

• Es fühlt sich gut an.
• Mein Arm fühlt sich seltsam an.

But in an infinitive or subordinate clause, it stays together:

• Es scheint sich besser anzufühlen.
• ..., weil mein Ellbogen sich besser anfühlt.

Because both parts describe what is happening or true right now.

• Der Arzt verbindet meinen Daumen = the doctor is bandaging my thumb
• mein Ellbogen fühlt sich schon besser an = my elbow already feels better

German often uses the simple present where English might use either:

• The doctor bandages my thumb
• The doctor is bandaging my thumb

In this context, English usually prefers is bandaging, but German just uses the normal present tense.

Yes, very often German does use the definite article with body parts, especially when the owner is obvious.

For example, you might hear:

• Der Arzt verbindet mir den Daumen.

Literally this is more like:

• The doctor is bandaging the thumb for me

This structure is very idiomatic in German:

• mir = to me / for me
• den Daumen = the thumb

But meinen Daumen is also completely understandable and natural, especially if you want to be explicit.

So both patterns exist:

• Der Arzt verbindet meinen Daumen.
• Der Arzt verbindet mir den Daumen.

The sentence you were given is a bit more direct and beginner-friendly because it clearly shows whose thumb and elbow they are.

Because besser means better, which shows improvement.

The sentence is saying the elbow feels improved compared with before.

• gut = good
• besser = better

So:

• Mein Ellbogen fühlt sich gut an. = My elbow feels good.
• Mein Ellbogen fühlt sich besser an. = My elbow feels better.

With schon, the idea becomes:

• My elbow already feels better.

Yes. Ellbogen is a normal German word for elbow.

You may also see Ellenbogen, which is very common too. Both are used, though Ellenbogen is often more common in modern standard German.

So learners should recognize both:

• Ellbogen
• Ellenbogen

Both mean elbow.