Review finds a lack of evidence for use of selective nerve root blocks for diagnosing lower back pain
17 May 2019
There is a lack of evidence for the effectiveness of a common test used to identify patients who would benefit from back surgery, a systematic review by NIHR CLAHRC West researchers has found.
Selective nerve root blocks (SNRB) are already used in clinics to aid back pain diagnosis and identify patients that would benefit from surgery. But the reviewers found only a handful of studies – all low scientific quality – that investigate the accuracy of this test. The evidence available shows that SNRB is not an accurate or reliable way to identify the patients who will benefit from back surgery.
It can be difficult to diagnose the exact cause of lower back and leg pain. Finding out whether a patient is experiencing lumbar radiculopathy – pain from a nerve that connects the back to the leg, also known as a ‘pinched nerve’, – or a different type of back pain is crucial when planning treatment.
Nerve roots exit the spinal cord and divide into nerves that travel to the arms and legs. Some patients with radiculopathy may benefit from spinal surgery to relieve pain and reduce disability. In most patients, nerve root pain is diagnosed through symptoms and scans. But these tests aren’t always reliable, so diagnosis can be difficult.
When patients have an uncertain diagnosis, doctors often use SNRB as an additional test to help decide whether surgery will be effective. An SNRB involves injecting a local anaesthetic around one or more nerves in the lower back. The patient’s responses can help confirm if one of the numbed nerves is the source of the symptoms and whether they are likely to benefit from surgery.
The researchers found six studies to include in the review. In two studies, patients were followed up for several months after surgery, to see if it resolved their back and leg pain. One study compared SNRB with observations made during surgery and another used both the observations during surgery and in the months after.
The remaining two studies compared the pain-killing effect of SNRB at the nerve root that was suspected of causing the pain, with the pain-killing effect in an unaffected ‘healthy’ nerve root. If SNRB is accurate, you would not expect a patient to experience a reduction in pain when injecting a healthy nerve root.
The results from each study were quite varied. Some concluded that SNRB was an accurate method, whereas others found the opposite. When pooling the results of the studies that used findings from during surgery, researchers found that SNRB correctly identified nine in 10 patients with a pinched nerve. However, SNRB was not accurate in excluding patients without pinched nerves: only half of the patients without pinched nerves were correctly identified.
When the results of the studies that followed up their patients to see if surgery had been successful were pooled, the team found similar results. Although SNRB could correctly identify nine in 10 patients with a pinched nerve, the test was even less reliable for excluding patients without pinched nerves: only one in five patients was correctly identified.