Made me laugh today... Surgery in general, including SRS, is made possible by the body's ability to heal: you cut it, it grows together again. The more it heals, the better.
However, if the healing - regeneration - was perfect and complete (like salamanders who grow whole new limbs), SRS would not be possible, because a year after surgery, everything would be back to how it was originally

To sum up: SRS is made possible by the fact that the body's healing is good, but not perfect