What is the difference between a grade 1, 2, and 3 sprain of a ligament?

Grade l - (mild) The ligament is stretched but still intact. Bleeding is minimal, and there is mild pain and swelling with no instability. There may have been a feeling of "popping".

Grade II - partial tear (rupture) of the ligament, visible swelling and noticeable tenderness, but without joint instability (or with mild instability). Grade III - a severe sprain: complete rupture of the ligament with significant swelling and with instability of the joint.