hi there, there is a possiblity that he may have passed the stone out in his urine. The abdominal pain
along with the low backache
also favours the passing of the stone down the ureter
. You can get a urine exam along with an x-ray KUB done for your husband and check with his previous x-ruy as to the position of the stone or you can also ask him to get an ultrasound
done to see the position of the stone and whether it is causing any obstruction. Take care.