Can knee and hip pain be related?

Yes: Yes. A painful knee can cause you to stand and walk in a different motion and angle causing hip pain.

Radiated pain : Inflammation and pain that comes from the hip can radiate to the knee. The knee pain coming from the hip often is a dull pain or aching pain that is difficult to locate precisely.

Somewhat: One does not cause the other, tho if u have arthritis generally in many joints it is not uncommon 2 have both. Having knee pain can very well b related. I have had patients present with knee pain only and have neg x-rays & xam , i would always x-ray their hips & would find some very severe hip disease on that side. Also pedi with knee pain always do hip eval. Not common but not rare either.

Yes: Anytime there is one joint involved, the adage is check the joint above and the joint below for issues. Many time these are also involved in pain issues. So your ankle/foot and hip are closely linked to the knee.