In 1985 I did something bad to my knee. I heard it crack and an elongated crunching sound and I couldn’t move my leg more than a few inches. A local GP said it was rheumatism and sent me for physio. For weeks this went on and I was eventually in such severe pain I took a second opinion. Thankfully the second doctor sent me for tests including an Arthogram X-ray. These tests found a shattered cartilage where it had broken into four pieces and fallen to the back of the knee. This needed an immediate operation. Some medical people need training in common sense.