I need Help with care plan for a patient with Decubitus Ulcer

i would ask your instructors to clarify what "theoretical knowledge" means, but my guess would be the pathophysiology of pressure ulcers. the pathophysiology of the medical condition is always something that you need to explore and understand when writing a care plan. it is needed to develop the related factors (etiology) on the nursing diagnostic statements.

see:

• http://www.nursingquality.org/ndnqipressureulcertraining/module1/default.aspx - pressure ulcer training tutorial (includes photos)
  
• http://www.hill-rom.com/usa/pdf/ctg285.pdf - guidelines for staging of pressure ulcers
  
• http://www.medicaledu.com/staging.htm - staging of ulcers
  
• http://ame-medical.com/staging_ulcers_guidelines.pdf - staging pressure ulcers
  

also read: http://www.merck.com/mmpe/sec10/ch126/ch126a.html - pressure ulcers, which includes the pathophysiology and information about the braden scale.

for help with the construction of a care plan see this thread: https://allnurses.com/general-nursing-student/help-care-plans-286986.html - help with care plans. if you search the student forums you will also find a number of threads regarding care plans for decubitus (pressure) ulcers. you begin this care plan by making a list of the signs and symptoms of a decubitus ulcer. the above weblinks will help you do that. your nursing problems (diagnoses) will be based upon those signs and symptoms.