New York, June 9 : The survival rate for cranial surgery performed by Inca surgeons in ancient Peru was twice more than those during the American Civil War, researchers say.
The study showed that trepanation -- the act of drilling, cutting, or scraping a hole in the skull for medical reasons -- was practiced for thousands of years from ancient Greece to pre-Columbian Peru and their success rates were up to 80 per cent, compared with just 50 per cent during the American Civil War.
"There are still many unknowns about the procedure and the individuals on whom trepanation was performed, but the outcomes during the Civil War were dismal compared to Incan times," said David Kushner, Clinical Professor at the University of Miami in US.
On the question that "how did the ancient Peruvian surgeons have outcomes that far surpassed those of surgeons during the American Civil War?" Kushner found "hygiene" as the key.
"If there was an opening in the skull they would poke a finger into the wound and feel around, exploring for clots and bone fragments," Kushner said, adding that nearly every Civil War soldier with a gunshot wound subsequently suffered from infection.
Civil War surgeons often used unsterilised medical tools and their bare fingers to probe open cranial wounds or break up blood clots, leading to higher mortality rates in the later time period.
"We do not know how the ancient Peruvians prevented infection, but it seems that they did a good job of it.
Neither do we know what they used as anesthesia, but since there were so many (cranial surgeries) they must have used something -- possibly cocao leaves.
Maybe there was something else, maybe a fermented beverage. There are no written records, so we just don't know," he explained, in the study, published in the journal World Neurosurgery.
The study also showed that ancient Peruvians significantly refined their trepanation techniques over the centuries.
"They seemed to understand head anatomy and purposefully avoided the areas where there would be more bleeding.
They also realised that larger-sized trepanations were less likely to be as successful as smaller ones," Kushner said.
"Physical evidence definitely shows that these ancient surgeons refined the procedure over time.
Their success is truly remarkable," he added.
The study was based on more than 800 prehistoric skulls with evidence of trepanation -- at least one but as many as seven telltale holes -- found in the coastal regions and the Andean highlands of Peru, with the earliest dating back to about 400 B.C.
Most of these were collected from burial caves and archaeological digs in the late 1800s and early 1900s and reside in museums and private collections today.