Kidneys and uterus are two separate organs and there is no relation between the two. Your doctor must be saying this because often stress during a surgery can precipitate renal colic (pain) attacks. Kidney stones are of four types: calcium oxalate stones, struvite stones, uric acid stones or cystine stones. Potassium citrate is used for the treatment of stones. I would suggest you to get an evaluation done from a urologist to determine the type of stone. Treatment modes include Extracorporeal Shock Wave Lithrotripsy (ESWL), uteroscopic stone removal and percutaneoud nephrolithotomy.
Then you can go in for hysterectomy uterus also.
I hope it helps. Take care and regards.