Breakdown of Es necesario flexionar la rodilla.
ser
to be
la rodilla
the knee
necesario
necessary
flexionar
to bend (a joint), to flex
Questions & Answers about Es necesario flexionar la rodilla.
Why do we use the infinitive flexionar here instead of the subjunctive?
You are right that Es necesario que... (It is necessary that...) triggers the subjunctive. However, we only use the subjunctive when specifying who needs to do the action. Because there is no que and this is a general statement applying to anyone, we just use the infinitive flexionar immediately after the impersonal phrase Es necesario.
Why does the sentence use la rodilla (the knee) instead of a possessive word like su or tu (your)?
In Spanish, it is the standard rule to use definite articles (el, la, los, las) instead of possessive adjectives (mi, tu, su) when talking about body parts. The context usually makes it clear whose body part it is, or in this case, it refers generally to anyone's knee.
Could I use doblar instead of flexionar to say "bend"?
Yes! Doblar is the everyday word for bending anything, including body parts (doblar la rodilla). Flexionar literally means to flex, and it is frequently used in fitness, medical, or anatomical contexts when talking about joints.
Why is necesario in the masculine form if la rodilla is feminine?
The word necesario is not describing the knee. It is part of the impersonal expression Es necesario (It is necessary). Because the "it" in this structure doesn't refer to a specific masculine or feminine noun, Spanish always defaults to the masculine singular form for the adjective.