Disks are blocks of cartilage between the vertebrae in our spine, that allow us to bend. If a disk herniates, the central portion “slips” through the outer shell, and can “pinch” a nerve coming out of the spinal canal. That causes back pain which usually runs down the nerve also. The most common place for this to happen is the very lower spine, affecting the long Sciatic Nerve that runs down the leg. In that case, the condition is called “Sciatica”.
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. In a severe case, a person can’t even hold their foot back (“foot drop”). There may also be loss of reflexes, especially the “Achilles reflex”) at the heel. There’s also a test called “straight leg raise” — the examiner lifts a leg & jerks the ankle back. Pain in the back, or especially on the other side of the back, suggests a herniated disk (but never pain just behind the knee)
Diagnosis is made by MRI, but there’s a big problem. Studies of MRIs on people without any symptoms at all have found lots of herniated disks. 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.
There are really only 2 treatments for herniated disks: 1) letting them get better on their own; and 2) surgery. 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 was cheap) if patient 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 strain!!!