MSFinals-2817

MSFinals-2817

A 56-year-old diabetic female comes in with cellulitis of the left foot, spreading from an ulcer on the plantar surface of the head of the left third metatarsal that had been present for 3 weeks before the onset of cellulitis. She was given oral flucloxacillin and the cellulitis improved, but after a week of treatment, the ulcer was still discharging and there was a tender area of swelling over the ulcer on examination. What is the most probable reason for this?