Grade 4 tear from Abbott et al. BMJ 2010;341:c3414.
Grade Damage
Grade I Only skin/vagina’s mucous membrane is damaged
Grade II Deeper damage in the vagina and/or perineum
Grade IIIa Less than 50% of the outer sphincter damaged
Grade IIIb More than 50% of the outer sphincter damaged
Grade IIIc Both outer and inner sphincter damaged
Grade IV Outer and inner sphincter damaged and also
rectum’s mucous membrane damaged
Grade III a, b and c as well as grade IV are so called anal sphincter tears.