What Causes Grinding And Cracking Feeling In Left Foot?

HI DOCTOR,MY PROBLEM IS BONES GRINDING AND CRACKING IN LEFT FOOT.I HAVE HAD PAIN FOR A COUPLE OF YEARS ON THE TOP OF MY FOOT, IT'S OSTEOARTHRITIS, HAVE HAD A CORTISONE INJECTION NEARLY THREE MONTHS AGO,I THEN NOTICED A GRINDING AND CRACKING FEELING IN MY FOOT,WHAT COULD THIS BE AND IS IT SERIOUS ? MANY THANKS DES DONNELLY