wound care on outer ankle/pressure ulcer

Hi all experts, a home patient has a pressure sore on outer ankle/external mallelous is the anatomy name, because it is open, I staged it as stage II, but I can see a white part, looks like a bone, so I still doubt about if it is right with stage II. For this particular site, it is skin wraping the bone, if it is open, it will easy to see the bone. It is a small wound, width less than 1 cm, and very little drainage. For this kind wound, what kind of dressing I should use? I feel the calcium alginate is for draining wound, this patient's wound has even no drainage, what I should care for this wound? What dressing is good? THANKSSSSSS!