The routine use of scans in patients with lower back pain does not improve their outcomes, US scientists say.
Imaging in the first month of low back pain is not recommended in the US or in draft guidelines of National Institute for Clinical Excellence (NICE). UK.
Researchers looked at six trials including more than 1,800 patients and found no benefit from the scans when patients were followed for up to a year.
Previous studies in the UK have shown similar results.
The researchers said the results were most applicable to the type of acute lower back pain assessed by a general practitioner.
They looked at pain, function, quality of life, mental health, overall patient-reported improvement and patient satisfaction in the care they received for up to a year after their initial treatment.
All the patients were randomised to receive either immediate scans or standard clinical care.
Some of the standard care group were offered scans if they had not improved within three weeks.
They did not find significant differences between immediate imaging with X-ray or MRI scans and usual clinical care either in the short-term - up to three months later, or the long-term - six to 12 months.
Dr Roger Chou, lead researcher from the Oregon Health and Science University said some doctors still do it routinely, "possibly because they aim to reassure their patients and themselves, to meet patient expectations about tests or because reimbursement structures provide financial incentives to image".
He added: "Clinicians should refrain from routine, immediate lumbar imaging in patients with acute or sub-acute low back pain and without features suggesting a serious underlying condition."
In the paper published in the Lancet, the researchers say rates of MRI scans for back pain are rising according to figures from US medical programme Medicare.
They think patient expectations and preferences for imaging should be addressed, because in one trial 80% of patients with low back pain would undergo radiography if given the choice.
"Educational interventions could be effective for reducing the proportion of patients with low back pain who believe that routine imaging should be done."
Dr Dries Hettinga, head of research at the UK charity Backcare, said: "While back pain is very common, we still have a very poor understanding of this condition and its causes.
"Health professionals play a vital role in reassuring patients.
"While it may seem that sending patients for an X-ray or MRI can provide this reassurance, the scans often reveal very little.
"With the right information and support, most people are able to manage their pain and find that it gets better within days or weeks."
The draft guidelines from NICE say X-ray and MRI investigations of the spine should be limited to when tumours, breaks, fusions or serious inflammation and infection is suspected.
It advises all people with lower back pain to exercise, if necessary in supervised groups, and that doctors should be able to offer a course of manual therapy or acupuncture, BBC reported.