Nerve blocks to reduce low back pain caused by spinal nerve impingement or compression is a fairly common way to treat this problem. But the nerve root is usually located deep in the spine and it is underneath a tough ligament called the lumbosacral ligament. Getting to the nerve with a long, thin needle is essential.
In some people, there is an arch of bone that is wider than normal. It covers the nerve enough that the needle can’t pass through to the nerve without puncturing it. Ultrasound-guided treatment can help guide the surgeon. The multibeam technology allows the surgeon to see as he or she tilts and/or rotates the needle. By slowly pushing forward into the soft tissues and seeing the probe on the ultrasound monitor, accurate placement of the needle is possible.
Anatomical variations like this can prevent the needle from reaching its desired location. That’s one reason you might not qualify for this procedure. Obesity and osteoporosis (brittle bones in danger of breaking with needle puncture) are two other risk factors for an unsuccessful attempt at a nerve block.
Surgeons are advised to use fluoroscopy (real-time 3-D X-rays) before attempting a nerve block. Fluoroscopy provides a pre-scan before ultrasound-guided injection. The surgeon uses these X-rays to look for any anatomical variations in form or structure of the spine that could prevent accurate probe/needle placement. And the X-rays help the surgeon find the best spot for probe/needle advancement and placement.
Evidently something in the pre-procedure work-up placed you in an at-risk category for a nerve block. You’ll need to discuss the particulars with your surgeon to find out why you aren’t a good candidate for this treatment and what your other options might be at this point.