I think the big, rather hard lump of a third knee is a hematoma. My knee was bruised pretty badly, and I think this is how it healed. I know it will eventually break down and be reabsorbed into my body, but for now, it's just a weird blob. I still don't know what the rough, crackling feeling on the surface is. Often inflammation can feel this way, but I would think inflammation would affect my joint mobility, and it's fine. I just don't know.
Have you ever had a long after-effect from a skinned knee? A hematoma, or unidentified lump? Should I just keep ignoring this?