In a ulcer over skin if there is undermined edges it suggests

Flat sloping venous or septic, often with a transparent healing edge along pa of its circumference. Punched-out syphilitic, trophic, diabetic, ischaemic, leprosy. Undermined tuberculosis, pressure necrosis paicularly over the buttocks, carbuncles. Raised rodent ulcer , often with a slightlyrolled appearance. Raised and eveed carcinoma Hamilton bailey 19th edition Pg 64