Me di un golpe en la rodilla. ahora la tengo (hinchar).

The correct conjugation of the verb "hinchar" that fills the blank is:

- Me di un golpe en la rodilla. Ahora la tengo hinchada.

Explanation:

The translation of the sentence is:

- I hit my knee. Now I have it swollen.

Swelling is the reaction caused by a blow or contact with an irritating substance, it is characterized by the redness of the area, pain and increased volume to the point that it is fully palpable with touch.

As in English, when after the verb "tener", which is "have" in English, another verb is used, regularly the latter is conjugated in Past Participle. In the case of the verb "hinchar" its conjugated form in Past Participle is "hinchado" or "hinchada" taking into account the gender of the noun to which it refers, as "rodilla" is a female noun, the right conjugation is "hinchada".