cause of lower back pain shooting down leg when standing still for a few minutes

The pain that appears after a few minutes of standing still and shoots down the leg is a classic mechanical loading pattern, and the most likely culprit is lumbar spinal stenosis made worse by the loss of the spinal canal's reserve capacity, not a simple disc bulge.

The mechanism is venous congestion and neuroischemia. When you stand still, gravity pools blood in the epidural venous plexus. The veins engorge, the already-narrowed lateral recess or foraminal space gets tighter, and the nerve root loses its oxygen supply. That is why the pain is positional: it is not the disc pressing on the nerve like a finger on a wire, it is the nerve suffocating inside a closed compartment. The classic name is neurogenic claudication, and it is a disease of the canal's cross-sectional area, not of the disc's height. The evidence for this is direct: a retrospective study of 114 patients with lumbosacral radicular pain found that the location, type, and size of the disc herniation did not predict long-term outcomes after epidural steroid injection, except that extruded herniations needed repeat injections more often [1]. That tells you the disc is not the whole story. The same study showed the average pain score dropped from 4.8 to 1.8 on a 0-10 scale after the injection, which works by shrinking the inflamed nerve and reducing the venous congestion, not by changing the disc [1].

The differential is narrow but important. True neurogenic claudication from spinal stenosis is the top suspect when standing still is the trigger and walking also brings it on, but sitting or leaning forward (which opens the canal) relieves it. If leaning forward does not help, think of a synovial cyst at the facet joint, which can also engorge with standing. If the pain is worse at night and wakes you, think of an inflammatory cause like ankylosing spondylitis, but that is not positional in the same way. If the pain is sharp, electric, and shoots below the knee with a cough or sneeze, that is a disc herniation with nerve root compression, but that typically hurts with sitting, not with standing still. The key discriminator is the relief position: flexion helps stenosis, extension worsens it. The evidence base for this exact presentation is thin because most studies lump "radicular pain" together without separating the standing-still trigger. The 2021 study is the only one in the retrieved records that follows patients long-term, and it is a telephone follow-up, not a randomized trial, so the confidence in the treatment effect is moderate, but the mechanism is solid [1].

The honest gap: nobody has run a trial comparing surgery, injections, and physical therapy specifically for the standing-still variant of radicular pain. The natural history is not well documented. What is known is that the pain is real, it is ischemic, and it will not resolve with rest alone because the problem is the canal's geometry, not the muscle. If the pain is accompanied by leg weakness, bowel or bladder changes, or numbness in the saddle area, that is cauda equina syndrome and requires immediate imaging, not a wait-and-see approach. For everyone else, the evidence supports a trial of transforaminal epidural steroid injection, which the 2021 data shows has a durable effect at four years for most people, but the evidence is a single retrospective cohort with no control group, so the true benefit over natural history is unknown [1]. The confidence is moderate that the mechanism is venous congestion and neuroischemia, and low that any specific treatment beats doing nothing, because that study has not been done.