Grade 2 – superficial skin damage. May present as a blister or as an abrasion. Partial thickness skin loss involving epidermis, dermis, or both. The ulcer is superficial and presents clinically as an abrasion, blister, or shallow center.
Grade 3 – full thickness skin loss not extending to bone or muscle. This grade is not usually painful. Full thickness skin loss involving damage to or necrosis of subcutaneous tissue that may extend down to, but not through underlying fascia. The ulcer presents clinically as deep crater with or without undermining of adjacent tissue.
Grade 4 – full thickness skin loss with extensive tissue damage through muscle and bone. Full thickness skin loss with extensive destruction, tissue necrosis, or damage to muscle, bone, or supporting structures (e.g, tendon, joint capsule). Undermining and sinus tracts also may be associated with Stage IV pressure ulcers.