A 48-year-old man with a history of diabetes presents to the emergency depament with a poorly healing right foot ulcer. The ulcer has been present for 1 month, and has never been treated. The patient denies fever or chills, and complains of mild pain at the ulcer site. His temperature is 37.6 C (99.6 F), blood pressure is 158/86 mm Hg, pulse is 94/min, and respirations are 18/min. The patient has diminished popliteal, posterior tibial, and dorsalis pedis pulses bilaterally, but the right side is worse than the left side. He has soft tissue swelling around the first toe with a 1 x 1 cm ulcer at the tip of the toe and surrounding erythema and purulent discharge. An x-ray film of the foot shows soft tissue swelling and signs of early bone destruction in the first metatarsal. What is the most likely cause of the bone destruction evidenced on the x-ray film?