The knee pain issue has come up before with Iodine supplementation.
I also had increased knee pain and still do if I overdo the Lugol's... in the left knee. I back off, it goes away.
Kidney sensitivity has also been noted. Olree states that Iodine has an influence on the urinary bladder and is necessary for the essential amino acid glutamine; also apparently prominent in the gastrointestinal tract. Could be all connected.