<s>[INST] context: Chronic osteomyelitis is the most common complication of acute osteomyelitis. If infection persists, pus and tiny sequestrated spicules of bone may continue to discharge through perforation in involucrum(cloacae). The hallmark of chronic osteomyelitis is infected dead bone within a compromised soft-tissue envelope. The infected foci within the bone are surrounded by sclerotic, relatively avascular bone covered by a thickened periosteum and scarred muscle and subcutaneous tissue. This avascular envelope of scar tissue leaves systemic antibiotics essentially ineffective. * Secondary infections are common, and sinus track cultures usually do not correlate with cultures obtained at bone biopsy. * Multiple organisms may grow from cultures taken from sinus tracks and from open biopsy specimens of surrounding soft tissue and bone. symptoms Pain, swelling. Discharging sinus. Bone thickening. Deformity. Joint stiffness. Shoening of limb, Pathological fracture. Sinus track malignancy. ref : maheswari 9th ed [/INST] question: An 18yr old male presents with a draining sinus on his left leg with pus discharge and discharge of bony pieces since 3 months. the diagnosis is | options: A: Chronic osteomyelitis B: Ewings sarcoma C: Osteoid osteoma D: Cellulitis | answer: A </s>