As millions await Pope Francis' first visit to the United States, a new scientific analysis suggests the familiar papal blessing hand gesture actually resulted from an injury to St. Peter's ulnar nerve.

The so-called "hand of benediction" — a half-open hand, with pinky and ring finger curled to the palm — has been used by popes throughout the centuries.

Bennett Futterman, M.D., an anatomy professor at New York Institute of Technology College of Osteopathic Medicine and former orthopedic surgeon, reports his review of studies of art, history, and religious practices has led him to conclude St. Peter suffered an injury to the nerve. It powers the muscles that allow the ring and pinky fingers to stretch away or extend from the palm.

"Peter, the first pope, had an ulnar nerve injury and everyone copied him," said Dr. Futterman, whose study is published this month in the journal Clinical Anatomy. "Imitation is a great form of flattery. Out of respect for St. Peter, the other popes followed with that same pattern."

Dr. Futterman noted that many past popes — and those depicted in thousand-year-old frescoes and sculptures — assumed the traditional hand of benediction pose. But he suggested papal blessings were likely intended to be given with an open hand, rather than a partial fist.

"A fist has always been a symbol of war — it's never a positive position," he said. "No holy man would ever bless the faithful, a crowd, or followers, by making a fist."

Dr. Futterman said he now plans to research what caused St. Peter’s ulnar injury.

"There's some evidence beginning to emerge that this may have been a leprosy infection affecting the ulnar nerve," he said.