Spinal fusion is one of the most common surgeries in America, but there are concerns that some doctors are performing it unnecessarily. The procedure joins two or more adjacent vertebrae, often with metal rods and screws, and can result in paralysis or life-threatening complications. For this six month investigation, we built a database from previously unreleased government records. It showed for the first time how many spinal fusions each surgeon in the country performed on Medicare patients, under the billing codes used most commonly for "degenerative" conditions that cause back pain. Half a dozen experts on medical billing and spine surgery told us that focusing on these codes would be the most effective way to identify abuse. We exposed that a small group of doctors performed far more of these lucrative but potentially dangerous procedures than their peers. Some of them were also banned or suspended from hospitals or settled lawsuits alleging unnecessary surgeries. Our findings were so alarming to the president of a top neurosurgery society that he called on authorities to look into these doctors. We also put the database online, made it easily searchable by patients, and provided guidance from experts on how to interpret it.