Question

When a skin graft (called a "free flap graft") is disconnected from the vascular and nervous supply, this is coded using the root operation of?

Answer 1

The answer would be the replacement

Replacement in ICD-10 can be defined as putting a material (biological or synthetic) that takes the place or function of a portion of a body part. 
A skin graft is collected from a part of the body to cover another part that needs the skin so it should be a replacement operation.
Other examples would be bone graft, valve replacement, or total knee replacement.