<prompt> Non-healing sinus is a common clinical feature is chronic osteomyelitis. The most common frequent cause for this presentation is:Resistant organismsRetained foreign bodyPresence of sequestrumIntraosseous cavities  <response>: C- Due to necrosis pieces of dead bone separate as sequestra varying in size from spicule to large segment. It is lighter than live bone and normal pattern of bone is lost. It acts as nidus and is most common cause of non healing sinus in chronic osteomyelitis. 