Skin loss extending to fascia, muscle and Bone, belongs to which grade of pressure sore?

Grading of Pressure Sores : Grade 1 - Non blanchable erythema. Grade 2 - Prtial thickness skin loss extending to epidermis and dermia. Grade 3 - Full thickness skin loss extending to subcutaneous tissue. Grade 4 : Skin loss extends to fascia + muscles + Bone or tendon or Joint.