Die kleine Wunde am Daumen tut kaum noch weh, wenn ich ruhig bleibe.

Because Wunde is a feminine noun, and here it is in the nominative singular because it is the subject of the sentence.

After die in the nominative feminine singular, the adjective takes -e:

• die kleine Wunde
• die alte Frau
• die rote Blume

So kleine is the correct weak adjective ending here.

Wunde is in the nominative case.

You can tell because it is the thing doing the action in the sentence grammatically — it is the subject of tut weh:

• Die kleine Wunde tut weh.

Even though a wound is not actively “doing” something in a real-world sense, it is still the grammatical subject of the verb.

Am is a contraction of an dem.

• an + dem = am

Here, dem Daumen is dative singular, because an is being used in a location sense: the wound is on/by the thumb, not moving toward it.

So:

• die Wunde am Daumen = the wound on the thumb

This is very common in German:

• am Tisch = at the table
• am Fenster = by the window
• am Arm = on the arm

Because am already tells you that the noun is in the dative here.

Since am = an dem, the article must be dem, not den.

• dem Daumen = dative singular
• den Daumen = accusative singular

If you said an den Daumen, that would usually suggest motion toward the thumb, not location at/on the thumb.

German often uses wehtun to express that something hurts.

The basic verb is:

• wehtun = to hurt, to cause pain

In a normal main clause, it splits:

• Die Wunde tut weh.

That is because it behaves like a separable verb in this use:

• tun is the conjugated part
• weh goes to the end of the clause

Compare:

• Mein Kopf tut weh.
• Der Rücken tut weh.

Because in a main clause with a conjugated form of wehtun, the verb is split:

• tut goes to the normal verb position
• weh goes to the end

So:

• Die Wunde tut weh.

This is similar to separable verbs such as:

• Ich stehe auf.
• Er kommt an.

With wehtun, you will often see:

• Es tut weh.
• Mein Bein tut noch weh.

Kaum noch means something like hardly any more or barely still.

The two words work together:

• kaum = hardly / barely
• noch = still / any more, depending on context

So kaum noch weh tun means the pain is now very slight compared with before.

Compare:

• Es tut noch weh. = It still hurts.
• Es tut kaum weh. = It hardly hurts.
• Es tut kaum noch weh. = It hardly hurts any more.

That last one strongly suggests improvement over time.

Because noch adds the idea of continuing from before until now.

Without noch:

• Es tut kaum weh.
  This just says the pain is slight.

With noch:

• Es tut kaum noch weh.
  This suggests it used to hurt more, but now it barely still hurts.

So noch gives the sentence a clear change-over-time feeling.

Both could make sense in some contexts, but bleibe is more natural here.

bleiben means to remain / stay, so:

• wenn ich ruhig bleibe = if/when I stay still / remain calm / keep still

Here it suggests a continued state: as long as I do not move around or agitate the thumb, the wound hardly hurts.

By contrast:

• wenn ich ruhig bin

can also mean when I am calm/quiet, but it often sounds more like describing your state in general rather than emphasizing remaining that way.

In this sentence, bleibe fits the idea better.

It most likely means still or not moving much here, though ruhig can also mean calm.

German ruhig has a wider range than English calm. Depending on context, it can mean:

• calm
• quiet
• still
• steady
• relaxed

In this sentence, because it is about a thumb wound, ruhig bleiben probably means something like:

• keep still
• don’t move around too much
• stay calm and physically quiet

So the exact nuance depends on context.

Because wenn introduces a subordinate clause, and in German subordinate clauses, the conjugated verb usually goes to the end.

So:

• wenn ich ruhig bleibe

Structure:

• wenn = subordinating conjunction
• ich = subject
• ruhig = predicate adjective/adverbial
• bleibe = verb at the end

This is one of the most important German word-order rules.

Compare:

• wenn ich müde bin
• weil er keine Zeit hat
• dass sie heute kommt

It can be understood as either if or when, depending on the context.

German wenn is often used for:

1. repeated or general situations = when
2. conditions = if

In this sentence, it is a bit conditional:

• if I keep still, it hardly hurts any more

But English when I keep still could also work, depending on the intended meaning.

So wenn is natural here because the sentence expresses a condition linked to a situation.

Because ruhig is not directly describing a noun here. It is a predicative adjective, used with bleiben.

In German, predicative adjectives do not take adjective endings:

• Ich bin müde.
• Sie bleibt ruhig.
• Das ist gut.

But when an adjective comes before a noun, it does take an ending:

• die ruhige Stimme
• ein müder Mann
• das gute Wetter

So:

• ich bleibe ruhig = correct
• ich bleibe ruhige = incorrect

The infinitive is wehtun.

Examples:

• Die Wunde tut weh.
• Die Wunde hat wehgetan.
• Die Wunde wird wehtun.

In everyday writing and speech, you may often see it treated as one verb in infinitive forms, but split in a finite main clause:

• wehtun → infinitive
• tut weh → present tense main clause

Yes, absolutely.

• die kleine Wunde am Daumen = the small wound on the thumb
• die kleine Wunde an meinem Daumen = the small wound on my thumb

The original sentence is more general and slightly more compact. Adding meinem makes the possession explicit.

Both are natural; the choice depends on how specific the speaker wants to be.