Translation:They are the only ones that know how my knee is.
in another comment section somebody said that you use el and la (la rodilla), which is translated as my knee, because it is automatically assumed that it is yours. this was also done so far in all the correct answers DL accepted, so can somebody explain to me, why "mi rodilla" is necessary here? Thank you in advance
Danilo, in those other examples, the subject of the sentence is the same person whose body parts are being talked about, so with no possesive adjective like, mi, su, tu, it is automatically assumed that the body part belongs to the subject. However in this sentence, the subject is they and the knee belongs to me, so I must use the possessive adjective, otherwise it would refer to their knee, which is too weird, even for DL :-)
I tried to translate by listening only to the audio and thought the sentence had a quesa (que saben) somewhere. I hope this inability to differentiate between words when spoken in a regular pace goes away with time, any tips people? :D ( ( Besides regular practice of course :) )