Defining Terms in Spine Medicine


Why in medicine do we have so many terms to describe the same thing? Is it frustrating as a patient to hear that you don’t have a “disc herniation” you have a “disc bulge” from 2 different clinicians while the radiologist’s report called it a “disc protrusion or extrusion”?

Not uncommonly treatment is diverted by clinicians based on the confusion, lack of understanding or just plain misunderstanding of this medical terminology. I will give you my humble simplification of these terms:

Disc Bulge – A normal physiologic or age-related rounding or flattening of the disc cartilage. Capable of causing some mild numbness, tingling or pin and needles but no pain.

Disc Herniation – A pathologic condition where the center nuclear material migrates through the cartilage seen most commonly over a prolonged period of repeated flexion and/or rotation movements. Capable of causing back and/or leg pain. This occurs as enzymes are released from this center nuclear material and less commonly, in fewer than 5% of patients, weakness. An estimated 40% of people who never had back or leg pain will have a disc herniation on an MRI scan. Types of disc herniations:

Protrusion – This herniation is broader than it is deep.

Extrusion – This herniation is deeper than it is broad.

Sequestration – This herniation has a free fragment that is no longer attached to the rest of the disc.

All 3 of these above terms are forms of herniations whether the term herniation appears or not on a radiology report.

The following terms in spine care are misleading and do not describe how discs herniate: Disc Rupture and Slipped Disc.

First, discs do not rupture nor slip. When a disc herniates the nucleus (inner 2/3) it has to “worm” its way through the cartilage (outer 1/3 of the disc that is called the anulus) most commonly from repeated flexion and/or rotational movements.In fact, it takes about 25,000 repeated flexion movements to herniate a normal disc. So why does it seem that you have symptoms of low back pain after a simple movement of bending forward (flexion)?As the nucleus worms its way through the anular fibers that overlap at about 65 degrees with each of the thousand flexion movements we make every day you don’t feel or know this process is happening. Only the outer most fibers have a nerve supply, so you don’t feel it till it is too late and the nucleus has herniated through the anulus.

Now for the good news. This process, often times, can be reversed by certain exercises. Most commonly with press-ups and standing end range extension. If done correctly at about 10 reps every 2 hours while you are awake some studies, by McGill, and others have shown this to be true in both cadaver and human research. Almost all physical therapists, some physicians as well as chiropractors know them well and will give you these exercises as the first line of treatment when you herniate a disc.

Anular Tear – This term applied to tears in the cartilage portion of the disc which in some cases is and in other cases is not painful.

Stenosis – A term applied to a narrowing of the spinal canal. When symptomatic, the patient typically will say they are worse with standing and walking and relieved with sitting or forward bending. Don’t be confused if a radiology report fails to contain this term and you see narrowing of the central or nerve canal. This narrowing is another way to say stenosis. Interestingly, by the time we are in our nineties we will all have stenosis on an MRI scan but not all will be symptomatic.

Degenerative Disc Disease – This is a term that will no longer be used in the future as it implies a disease process is present. Most of the time this is thinning of the disc and is a normal process of wear and tear as we age.

Spondylosis ( spondylosis deformans) is best thought of as normal wear and tear that eventually all of us will have after our 20’s. Not to be confused with arthritis ( it does not end in itis. It ends in osis) arthritis = spondylitis. With spondylosis there are also reactive bone spurs that help stabilize the bones above and below the disc that is going through the wear and tear. So these spurs, often thought of as negative, are actually necessary for stability, and not a painful process.

Spondylolysis refers to a fracture of the spine that occurs between a process that goes up and one that goes down on each side at the back of the spine making up the Facet Joints.

Three stages exist:

Stress Reaction – bone swelling or edema but no fracture (seen easily on MRI)

Stress Fracture – bone has a crack but not a full thickness one (x-ray is normal but seen on CT or MRI)

Full thickness Fracture – seen on x-ray, CT and MRI

Spondylolisthesis – a slip of one vertebrae on the one below. Most commonly seen at L5-S1, the lowest level. Multiple types are seen but the 2 most common are:

Isthmic – a spodylolysis is seen on both sides. Usually at L5-S1 level.

Degenerative – no fracture (or Spondylolysis) is present. But the disc and facet joints degenerate enough to allow this to occur.

There are 5 grades of spondylolisthesis based on the percent of slippage:

Grade I 25% slip or less

Grade II 25-50% slip

Grade III 50-75% slip

Grade IV 75-100% slip

Grade V > 100% slip or so-called Spondyloptosis