By Dr. Jeffrey Peng, MD · Published March 5, 2026 · 6 min read Watch the Full Video If you have been told you have knee arthritis, your doctor likely used an X-ray to assess the severity of your condition. The most widely used classification tool for this purpose is the Kellgren-Lawrence (KL) grading system , which rates knee osteoarthritis on a scale from 0 to 4. A grade of 0 indicates no signs of osteoarthritis, while a grade of 4 represents severe, bone-on-bone arthritis