Solely due to organisms like staphylococcus aureus / salmonella Infections begins at metaphysis - due to slow down of blood in that region - cause colonisation of these organism Starts of inflammation -( modern days emperor for diseases) ... Necrosis of dead bone ( sequestrum), surrounding the pus Then around the sequestrum is new bone formation called involuctrum - which later discharge the pus through sinus tract called cloaca via skin