Back pain is one of the most common reasons people visit a doctor or miss work.

Experts say while most patients have no serious underlying condition causing the pain, doctors often immediately order imaging procedures that can check for problems like herniated disks, muscle injuries, arthritis or broken bones.

Dr Roger Chou of Oregon Health and Science University in Portland and colleagues assessed the results of six studies involving 1,800 people with lower back pain.

Patients who had no sign of a serious underlying cause but were immediately given an imaging test fared no better than other patients who received standard treatment but no imaging, the researchers wrote in the journal Lancet.

The findings apply in particular to the type of lower back pain usually assessed by a family doctor, the researchers said. They urged doctors to refrain from ordering X-rays, MRIs and CT scans without some concrete sign that a problem exists.

The imaging tests can be expensive, and the X-ray and CT scans expose patients to low doses of radiation that potentially raise cancer concerns, the researchers said.

"If there are no warning signs pointing to a serious cause of low back pain, imaging is almost never helpful to guide treatment. Routine imaging of patients with low back pain is a waste of health care resources," Dr Michael Kochen of the University of Goettingen in Germany, who wrote a commentary accompanying the study, said by e-mail.

"Additionally, imaging has some potentially serious side effects," Kochen added. "Radiation exposure is an important public health issue, particularly in women where imaging of the low back pain exposes ovaries to radiation."

Kochen said that while magnetic resonance imaging does not involve radiation, it is expensive.

"Some clinicians still do lumbar-spine imaging routinely or without a clear indication, possibly because they aim to reassure their patients and themselves, to meet patient expectations about diagnostic tests," or other reasons, the researchers wrote.