Adam Hammond, a former U.S. Army parachutist, had logged more than 1,000 jumps. But his most recent jump, and perhaps his last, was just for fun. Unfortunately the chute malfunctioned, and Hammond slammed into the ground at 45 mph.

"No one expected me to live," Hammond said.

He did, however. The 26-year-old woke six weeks after the accident to find he had a broken femur, a shattered pelvis and a severed spine.

And a lot of pain.

Hammond had several surgeries and a lot of physical therapy over the next two years, but chronic pain persisted.

Now surgeons at the Center for Pain Relief in Charleston, W.Va., have installed a "pacemaker for pain" into his lower back. The device, about the size of a silver dollar and developed by St. Jude Medical in Minnesota, is said to be the world's smallest, longest lasting, rechargeable neurostimulator to treat chronic pain.

The Eon Mini , as it is named, delivers mild electrical pulses to the spinal cord which interrupt or mask the transmission of pain signals to the brain.

Scientists still struggle to understand how pain works. According to the National Institutes of Health, 90 million people in the United States suffer from chronic pain. The American Pain Foundation estimates that chronic pain costs approximately $100 billion per year in lost work time and healthcare expenses.

The rechargeable device seems to be helping Hammond.

“I already have significant pain relief,” he said in a statement released today by St. Jude Medical. “I’m now able to walk twice as far, and I recently went to the movies with my best friend. It feels good to start getting my life back.”