Medica dicit femur et crus intra paucos dies bene sanescere posse.

The main verb is dicit = says.

It is singular because its subject is medica = the female doctor.
Even though femur et crus refers to two things, those words belong to the infinitive clause after dicit, not to the main clause.

So the structure is:

• Medica dicit = The doctor says
• femur et crus ... sanescere posse = that the thigh and lower leg can heal

Latin usually does not use a separate word for that after verbs of saying, thinking, knowing, and so on.

Instead, it often uses the accusative-and-infinitive construction:

• dicit = she says
• femur et crus ... posse = the thigh and lower leg to be able...

That sounds unnatural in English, so we translate it with that:

• The doctor says that the thigh and lower leg can heal well within a few days.

So that is understood from the grammar, not from a separate Latin word.

They are the subjects of the infinitive in indirect statement, so grammatically they are accusative.

However, both femur and crus are neuter singular nouns, and in Latin the nominative and accusative singular of neuter nouns are often the same.

So:

• femur can be nominative or accusative singular
• crus can be nominative or accusative singular

Here they are accusative because they depend on dicit in the indirect statement.

Because posse often takes another infinitive with it.

• posse = to be able
• sanescere = to heal / get better / recover

Together, sanescere posse means:

• to be able to heal
• more naturally in English here, can heal

So after dicit, Latin gives the whole idea in infinitive form: femur et crus ... sanescere posse.

Because medica is the feminine form, meaning female doctor or female physician.

• medicus = a male doctor
• medica = a female doctor

So the sentence specifically tells us that the speaker or subject is a woman.

Intra is a preposition that takes the accusative and means within or inside.

So:

• intra = within
• dies = days (accusative plural here)
• paucos = few (accusative plural masculine, agreeing with dies)

Together:

• intra paucos dies = within a few days

A learner may also notice that dies belongs to the fifth declension, which is why its forms look a little different from first- or second-declension nouns.

Bene is an adverb, and it modifies sanescere.

So it tells us how the healing happens:

• sanescere = to heal / recover
• bene sanescere = to heal well

It does not describe posse directly; it describes the healing itself.

Because sanescere usually means to become healthy, to get better, or to heal up. It is an intransitive idea: the body part itself recovers.

By contrast:

• sanare usually means to heal something, in a more transitive sense
• sanari would mean to be healed

Here the idea is that the femur and lower leg recover, so sanescere is a very natural choice.

• femur = thigh
• crus = lower leg, often the part from the knee downward; depending on context, it can sometimes be translated more broadly as leg

So the sentence refers to two different parts of the leg, not to the whole leg as one unit.

Latin word order is much more flexible than English word order, because the endings show the grammatical relationships.

This sentence is arranged quite naturally:

• Medica first: the topic or subject
• dicit early: the main action
• then the content of what she says
• sanescere posse at the end: the verbal idea of the indirect statement

A different order could still be grammatical, but this order is clear and straightforward.

Because Latin is referring to one thigh and one lower leg.

Latin often uses the singular for individual body parts when one of each is meant. So this does not mean thighs and legs in general; it means a particular thigh and a particular lower leg, probably belonging to one patient.