Sciatica means inflammation of the long sciatic nerve, which exits the lower spine and runs down the outside of the leg to the top of the foot & big toe. This is usually caused by protrusion (herniation) of a disk onto the nerve (see Diagram — Anatomy of the Spine). Disks, blocks of cartilage which allow our spine to bend, can weaken with age, but can also herniate from trauma, which usually involves bending, twisting, or lifting.
We suspect a herniated disk is the cause of back pain that runs down one leg (strains & sprains only hurt in the back). Sometimes pressure on the nerve is enough to affect strength; in the case of the Sciatic Nerve, weakness mainly affects holding up the big toe firmly, against resistance at first. If severe, a person can’t even lift their foot up (“foot drop”). See our topic Low Back Pain in terms of physical exam.
Diagnosis is made by MRI. Lots of people with back pain want to get an MRI, but there’s a big problem. Large studies of MRIs on people without any symptoms at all have found lots of herniated disks, even big ones. So just because the MRI is abnormal doesn’t mean that’s the cause of back pain. We only trust the MRI if the same nerve affected there also corresponds to the patient’s actual symptoms and physical exam.
There are really only 2 treatments for herniated disks: 1) letting them resolve on their own; and 2) surgery. Various pain medications can help with comfort. The strongest are opioids (narcotics, related to morphine), which can cause dependence and addiction, and shouldn’t be used for more than a week. Since most disks get better in 4 months, surgeons are reluctant to operate until then. They only operate sooner if there’s significant weakness (like foot drop).
So there’s no need for an expensive MRI until the point that surgery becomes a real possibility. And there’s certainly no need for an MRI (even if it were cheap) if a patient’s symptoms don’t seem like a herniated disk. Imagine doing surgery for a false-positive abnormality on MRI, when all they really had was a simple muscle strain!!!
We consider referral to an neurosurgeon when pain has lasted 2 months without starting to improve, or if it persists more than 3-4 months. We refer earlier if we find actual abnormalities on our physical exam, mainly true leg or foot weakness (not just due to pain), or complete loss of sensation (not just tingling). Nobody wants to operate if there’s a good chance things will get better on their own.
Neurosurgeons may try epidural injections first, although there’s no proof that this helps. Physical therapy may help back pain due to muscle strains or ligament sprains, but not due to herniated disks. Some people claim to be helped by acupuncture or chiropractic treatment, but placebo is also effective.