I am assuming that there is some serious skin issue there, like the very beginning of necrosis. Looking at the toenails it is obvious that they are unable to maintain good hygiene, their leg is way bigger than it should be and I would be surprised if they can walk longer distances. I would suggest that blood flow to the capillaries in their skin cells has been cut off/severely restricted and so the skin is beginning to die.  If this fattie keeps their legs they will probably get a stroke or a heart attack, something blood clot related. If it is bad enough that the skin on its limbs is dying then its heart/veins/arteries are most likely beyond repair.