Your uncle has developed gangrene of foot due uncontrolled diabetes
.A general term DIABETIC FOOT
has been given to such cases.
The major factors involved in it's causation are ischemia,neuropathy,and infection and delayed wound healing
The management requires a proper evaluation of foot by getting
CT FOOT to see the bone infection
Arterial and venous Doppler of lower limb
Treatment would involve prolonged antibiotic therapy with proper amputation of the affected part.
A reconstructive surgery
is to be done properly to avoid future occurrence of gangrene by restoring proper blood flow to the foot.
I hope it helps.