News Release

1995-12-15 00:00:00

New understanding for back pain

University of Waterloo News Bureau

-- For immediate release

Researcher seeks new understanding of back problems

WATERLOO, Ont. --Lower back pain is the main research interest of some pace-setting work conducted by Prof. Stuart McGill of the University of Waterloo's kinesiology department.

Back pain is an extremely complex subject, with many injuries that seem to be virtually inexplicable. McGill thinks too much of anything -- even lying in bed -- can be harmful to the back. Certainly, one cannot tell from looking at a person whether he or she is likely to be a candidate for an injury. One has to understand the anatomy and biomechanics of the spinal musculature, as well as the ligaments, or other tissue with the potential to be injured.

McGill, with his team of graduate students, conducts much of his work in the occupational biomechanics and safety labs. There, a test subject's spine is modelled in the computer, so the person's muscles "drive" the computer's.

"We do this by detecting and recording muscle activity," he says. "Electronic sensors are attached to the skin of a subject to detect voltage changes as they are generated within a muscle group in action. We know there are functional units inside a muscle (motor units) that 'fire' -- create an electrical storm within the muscle -- during contraction.

"Our sensors pick up these firings and we use fairly sophisticated electrical signal processing technology to transform the electric signals and get a meaningful muscle force from it. It provides a way to be right inside the spine which in reality we cannot do; but we can simulate a spine in the computer and observe how it moves and examine the distribution of the muscle and other tissue loads."

By measuring the forces exerted on the ligaments, and the loads on the discs, McGill and his students can come up with answers to many questions. They can even assess the risk of injury to the discs during work being done in factories. Thus the research activities in his lab help answer the question: Why did one person suffer a spinal injury doing such-and-such a task, while another did not?

McGill also has a lab in which he can take a spine and load it (compression and shear loads) until it breaks, to find out at what point this happens and why the breakdown occurred. He uses pigs' spines for this work feeling they are suitable because they have a good deal in common, structurally, with the human spine. He can also do repeat testing on spines that are extremely uniform in size and strength.

"We determine the point where vertebrae will fracture, discs will herniate, and ligaments tear," McGill says. "Generally, disc degeneration is a disease associated with sedentary people. On the other hand people who tend to be overly active are more likely to suffer from arthritic bone formation, traction spurs, etc." Still, he says, there is no substitute for being "generally" fit and reasonably active -- not too much activity, but not too little.

McGill's concern over back injury is not in the area of muscle fatigue or occasional minor aches and twinges. He's more worried about serious tissue damage, where the muscle detaches from the bone, or where there is ligament or disc damage.

It is easy to understand how a back can be injured by lifting something heavy; it's not so easy to explain how someone can lift heavy objects at work all day long and not get an injury, and then be injured simply by bending over to pick up a newspaper at home.

McGill says such injuries occur and when they do, they often appear to be the result of a kind of "motor control error" in sequencing muscles to the point that one joint in the lower back over-rotates; so that for an instant, the passive tissues like ligaments are at risk of injury. This, McGill says, is more understandable than one might at first suspect, because the chances of such an event (over-rotation) are actually greater when loads are lower.

In his lab, McGill can check individuals' motor control systems. He is interested in subjects whose motor control systems are "wise" -- that is, they can handle new situations. In one series of tests he asked people to perform back exercises while they were being distracted, and reports the instrumentation shows "some people create inappropriate muscle forces which elevate their risk of injury. Such individuals have motor control systems that respond poorly and may benefit from specific functional training -- but this is a new and controversial area."

One frequently suggested solution these days is to minimize back injury by providing sedentary workers -- secretaries and other office personnel, for example -- with "ergonomic" chairs. McGill feels even these have limitations. They have to be adjusted to the needs of the individual user. And they won't necessarily work if you sit in them without moving for long periods of time. Workers have to be free to move about and stretch every so often. Backs, McGill feels, are made to be in motion.

People who continuously sit for eight hours a day will have a higher risk of disc problems than people who deliberately take regular breaks to give their backs a chance to recover. Standing up every once in a while helps disperse the stresses on your discs.

This, McGill feels, is primarily a matter of work organization. Instead of sitting for three or four straight hours and then standing for half an hour to do filing, a secretary might be better advised to get up get up every 50 minutes and do 10 minutes of filing at a time. Many suggested guidelines for doing heavy work -- bend your knees, keep your back straight, and so on -- cannot always be followed, unfortunately; a good deal depends on the job.

McGill is also aware of popular myths about avoiding back injuries and a variety of therapies. Some, he says, are helpful; others don't seem to have worked out well. "We have examined a variety of back-strengthening exercise programs. The idea is to find a way to train the supporting musculature in a way that will do the least amount of damage to the spine."

He notes that a number of doctors have been prescribing sit-ups to develop the abdominal muscles, but McGill feels some of these exercises are poor. If they compress the spine -- so it comes under a high compressive loading --injuries may be increased rather than rehabilitated.

"We have done some work that involved implanting electrodes into patients' deep muscles, and what we found was that when the spine is compressed, certain muscles -- called quadratus lumborum -- become active in order to stabilize the spine," he reports.

He feels "horizontal side support" exercises are among the best for strengthening these specific muscles, thus helping to stabilize certain types of back injury. But he warns that "sooner or later we're all going to experience some kind of a back problem."

The goal then is to prevent as much of this kind of injury as possible and to treat it as effectively as possible when it does happen. To this end McGill suggests the following rules: ¥ Don't do any single thing too long . . . and that includes lying in bed. Doctors get patients up quickly after spinal surgery to get the spine moving. ¥ Take rest breaks to give your back a chance to recover, whenever you are stooped over doing gardening, or sitting still for a long period of time, or lifting heavy weights. Stand up, rock slightly backwards; give your spine a rest -- this allows several tissues to equalize stress. ¥ When lifting, hold the load close to your body -- don't reach out and lift. ¥ Preserve the natural curve of your back when performing an exertion, and rotate your torso about your hips, not about the spine. ¥ Do not perform demanding exercises first thing in the morning because discs are hydrophilic. Overnight, they tend to soak up water and swell. It's easier to herniate a swollen, water-filled spine if you attempt a chore such as shovelling snow first thing in the morning. Wait until you've been up for a while and the discs have lost some water, reducing their stress.

McGill suggests taking breaks when driving long distances take breaks. He is evaluating a new kind of insert called the "back cycler" that has just come on the market and is intended to help release back tension by keeping the spine in motion while driving.

He is also asked by industry to advise in connection with back injury prevention, and testify in court in back injury lawsuits. As well, he speaks to various medial groups, "trying to encourage them to diagnose back injuries better. Doctors need to be able to tell patients whether their injury is in the muscle, disc, ligaments, or vertebrae. We have to know this to optimize the advice as to how a patient might prevent re-injury, or recommend treatment or rehabilitation to strengthen the tissue. We are actively trying to help educate medical people about these kinds of injuries -- they are experts in the treatment of injury, but not particularly good at prevention."

As for reducing the risk of injury on industrial jobs, he is currently looking into such questions as how many times a worker can be expected to safely lift a certain weight within a given period of time, and what is the safest posture to adopt. "We know that once in a while the motor system will simply fail, and allow tissue to become overloaded," he admits. "So we will never eliminate all back injuries; the objective is to minimize as many as possible."

His lab can do detailed functional assessments of injured workers, even to the extent of documenting the severity of a given impairment. "We have developed instrumentation that provides one of the most comprehensive three-dimensional examinations of spine and muscle function available, without any imaging such as x-rays.

"Spine motion and muscle usage have many characteristic signatures which allow us to assess if an individual is attempting to misrepresent their injury -- or, we can compare these signatures to our data base to document a bona fide disfunction. Sometimes the presence or absence of pathology is quite clear," McGill says.

Resources



Contact: Prof. Stuart McGill, (519) 888-4567, ext. 6761
Written by Bob Whitten
From Jim Fox, UW News Bureau, (519) 888-4444
Release no. 199 -- December 15, 1995

1995-12-15 00:00:00