Paul Halpern from Florida managed to save the severed digit and take it to the hospital, but doctors told him there was nothing they could do.
His insurance company wanted him have the remaining two-thirds of his finger amputated, 'New York Daily News' reported.
Halpern then visited Dr Eugenio Rodriguez, a Deerfield Beach general surgeon who used an innovative procedure called xenograft implantation to regenerate the finger.
Xenograft refers to the transplantation of cells from one species to another.
According to CBS Miami, Halpern had to apply pulverised pig bladder tissue to his wounded finger each day and cover it with a protective saline sheet.
Rodriguez said the powder stimulates stem cells in the finger to regenerate, which causes the growth.