In my father’s day and much of my career as a neurologist, the word “sciatica” was used to refer to pain in the lower back and leg, usually related to a disk protrusion compressing a nerve root in the lower back.

And so, it continues to this day and was the title chosen for a review article in the New England Journal of Medicine in 2015 by a former colleague of mine in Boston, Allan Ropper.

Allan is a full professor in neurology at Harvard University, senior editor for neurology of the same journal and one of the most astute clinicians I’ve known. He is also the author of one of the best neurology textbooks, now in its umpteenth edition.

Hence, my surprise when he wrote that review article covering all causes of lower back and leg pain under the misleading general title of “sciatica.” 

Properly applied, the term sciatica refers to lesions which affect the sciatic nerve, not the lumbosacral nerve roots in the immediate vicinity of the lumbosacral spine or the lumbosacral plexus formed from those roots within the pelvis. 

Far and away, the most common cause of lower back pain and often leg pain is age-related degenerative disease in the lumbosacral spine caused by compression of the fifth lumbar or first sacral nerve root or possibly both roots by herniation of disks, ligamentous thickening and hypertrophy of the posterior facet joints. 

Much less common are symptoms related to the sciatic nerve. This nerve is formed from the lumbosacral plexus within the pelvis, where the nerve is well beyond the lumbosacral spine. 

This sciatic nerve is the largest nerve in the body and comprised of two major divisions. The lateral division innervates muscles in the anterolateral calf and sensation to the same region and the top of the foot. The medial division innervates muscles in the posterior calf and most of the muscles in the foot and sensation for the bottom of the foot and back of the calf. 

Except for occasional benign masses or tumours within the pelvis, the lumbosacral plexus is well protected as is the sciatic nerve in its course through the sciatic notch to reach the proximal leg, because of the cushioning effect of the overlying beefy buttock and posterior thigh muscles.

But despite so much muscle, compression of the nerve can still cause symptoms. For example, the nerve may be compressed within the sciatic notch by an enlarged piriformis muscle through which the nerve passes on its way through the notch. 

More common is direct compression of the nerve caused by sitting too long on a hard seat with a bulky wallet, or these days, an iPhone, stuffed in the back pockets of pants. The latter is common in long-haul drivers, who often pay no notice to the growing tingling in the back of their leg and the sole of their foot.

Sometimes, the first time the driver is aware of the numb leg is when they jump down from the cab, only to stumble or even fall. Fortunately, recovery is usually quick.

Much less common is injury to the sciatic nerve by a misplaced intramuscular injection.

There is another cause related to exercise. I like to stay fit and sometimes push the limit. That happened in late November at the community centre, when I was working out on an elliptical trainer and developed pain in my left buttock and anterolateral and posterior calf muscles — enough to make me stop.

There was no back pain, nor was there weakness, but there was tenderness for sure when I palpated the sciatic notch, the pressure of which also caused tingling down the back of my thigh and calf.

Over the next few weeks, the symptoms resolved, but I haven’t used an elliptical trainer until recently and cautiously. 

It was a good lesson: Be careful of exercises that produce symptoms of muscle or nerve injury.

Perhaps some of my readers have had similar experiences, not necessarily with their sciatic nerve, but overdoing some exercises or perhaps, as some trainers rightly suggest, it may be wise to get professional advice about what exercises we do and, as important, how to do them safely. 

Dr. William Brown is a professor of neurology at McMaster University and co-founder of the InfoHealth series at the Niagara-on-the-Lake Public Library.