Back pain is one of the most common reasons Americans go to the doctor, and one of the fastest growing treatments is spinal fusion surgery. From 2001 to 2011, the number of spinal fusions in U.S. hospitals increased 70 percent, making them more frequently performed than even hip replacements. The growth has been attributed in part to improved technology, an aging population, and a greater demand among older people for mobility. But it has also sparked a debate over whether some surgeons are performing spinal fusions that are unnecessary and potentially dangerous. The procedure fuses together two or more vertebrae often with metal rods and screws, and can result in paralysis or life-threatening complications.

X-ray of spinal fusion Association for Medical Ethics

For decades, patients have had no insight into how likely their doctor is to recommend a spinal fusion, or whether they may be performing risky procedures that others would not consider appropriate. They had no way of knowing how many spinal fusions their doctor performed over a given period, what percentage of patients they performed the procedure on, and how that compared to their peers. This story makes much of that information public for the first time.

For this six month investigation, CBS News exclusively obtained part of a government database. We asked for, among other things, the number of spinal fusions each doctor in the country billed to Medicare from 2011-2012, under codes most commonly used for "degenerative" conditions that cause lower back pain. We put the entire database online and made it easily searchable by the public. We also provided guidance on how to interpret it and details about how it was compiled.

It is important to note that the data does not reveal whether any of the surgeries that a doctor performed were inappropriate, and includes many spinal fusions that are widely considered necessary. Still, experts say high numbers raise questions and serve as starting points for further investigation. We looked into some of the highest volume surgeons and found some were respected with unblemished records. Others were banned or suspended from hospitals or settled lawsuits alleging unnecessary procedures. All of them are still operating.

The data shows that a small group of doctors performed these procedures far more frequently than their peers. While the national average was 46 surgeries over the two year period, some did more than 460. While the average spine surgeon performed them on 7 percent of patients they saw, some did so on 35 percent. (Averages exclude doctors that performed 10 or fewer of these fusions. Medicare redacted those figures to protect patient privacy.)

There are multiple reasons why a surgeon may be performing a disproportionate number of fusions. Some may receive lots of referrals and treat more complicated cases. Others may believe the procedure is appropriate for patients that many doctors would not operate on. There is also a financial incentive to performing a spinal fusion. It can earn a surgeon thousands of dollars - and five times as much as less risky alternatives.

Some of the biggest concerns surround more complex fusions that join four or more vertebrae. The more vertebrae that a surgeon fuses, the more they are paid (all else being equal), but the risks increase for the patient as well. One study of complex fusions for stenosis (a narrowing of the spinal canal) found 1 in 20 led to life-threatening complications. When it came to these riskier surgeries, the discrepancy in the data was even larger. Some doctors performed more than 100, while the national average was less than 7. Overall, 5 percent of the surgeons did about 40 percent of the fusions on four or more vertebrae.

We shared these statistics with Dr. Daniel Resnick, Vice Chair of Neurosurgery at the University of Wisconsin School of Medicine and President of the Congress of Neurological Surgeons. He said they raise serious concerns, and suggest that while the majority of spine surgeons are careful about recommending fusions, some may be "operating outside of the generally agreed upon (based on common practice and literature supported guidelines) parameters."

Dr. Resnick added that Medicare, medical societies, and credentialing boards should use data like this to follow practice patterns and patient outcomes. He said surgeons with the highest numbers should be looked at closely and asked to explain themselves.

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