A 42-year-old woman with a 10-year history of type 2 diabetes mellitus presents with pain, erythema, and a non-healing ulcer over the plantar surface of her right foot. She reports stepping on a nail 8 weeks ago. On examination, the ulcer is 2 cm × 1.5 cm with purulent drainage and a foul smell. There is loss of protective sensation to monofilament testing. Blood glucose is 280 mg/dL. X-ray shows cortical irregularity and periosteal new bone formation in the metatarsal head. Which is the most appropriate next step in management?