What happen when ligament of lower spine tore?

Torn ligament? Without a fairly significant injury, a truly torn ligament (a sprain) is fairly uncommon. It is also difficult to diagnose without an mri. Presuming you have a torn ligament, treatment is based on if there is a risk of instability. If a minor sprain, rest, ice, anti-inflammatories and time usually heals. More severe injuries occasionally require surgery--falls, auto accidents, etc.