The rest of this website and my old website are concerned with my work since 1981 which started with my investigation of the cause of lumbar back pain. Over the years this took me into office chair manufacture, car seat design and manufacture, chiropractic, posture and exercise but has so far failed to get any recognition of the basic point which is contained in the following:
The lordosis in the human spine is difficult to explain in engineering terms. In fact it's impossible and all engineering explanations have been wrong. The real reason was shown by the anthropologist Owen Lovejoy in "The Obstetric Pelvis of Lucy". It is simply the maintenance of an adequate birth canal in the pelvis. (full details of this, and all other, references are in the paper The obstetric reason for Lordosis etc on this website)
The birth canal defines the shape and angle of the sacrum and this in turn results in the lowest two discs of the spine being wedge shaped by about 20 degrees. (Thick edge of disk anterior, thin edge posterior at L4/5 and L5/S.)
But note that this 20 degrees is far greater than the mobility of these joints in flexion. (Max nine to fifteen degrees. Piercy, Portek and Shepherd, Jonk and van Niekerk etc.) meaning that these discs will always remain wedge shaped in the same direction, even in full flexion-- as a long as there is nothing that distorts this evolved situation.
Sadly there is. It is one of the most common items in our civilised lifestyle. It is the chair or seat with a backrest.
A backrest will always tend to flex the lowest joints of the spine in comparison with unsupported sitting while at the same time extending or hyperextending those higher up. This should be predicted by any engineer and was clear from the tabulations in "The Influence -- -- -- Of Lumbar Support -- --" by Anderson, Nachemson et all.
Well, maybe it won't matter that these discs, instead of always remaining wedge shaped as they were evolved, are made to flex and extend like any other discs of the spine. Sadly it does matter. It matters very much, for the following reason.
In the chimpanzee, the strength of the spine increases with flexion of the lowest joints. This is because the origins of the back muscles on the pelvis are above the lowest spinal joints. With the changed shape of the human pelvis, this situation is reversed. The origins of the back muscles are now below the lowest joints. To any engineer this is obviously an over-centre mechanism and the strength of the spine will be reduced to almost nothing by flexion. This would mean that the human spine could be broken like a chicken leg where it connects to the pelvis.
This problem does not have an easy mechanical solution. It must have happened frequently to our earliest bipedal ancestors and some of them would very quickly have become food for the predators and scavengers of the savannah.
However, before the spine lost all its strength, there would be a phase when the lowest discs just began to flex beyond the parallel sided shape to the situation where the posterior edge of the disk was a bit thicker than the anterior edge. The nucleus would then, for the first time for that individual, tend to move towards the posterior edge of the disk. The proximity of the nucleus would be a new and unusual event for the nerves in the posterior annulus of the disk. Nerves that experience an unusual event will produce pain. In some individuals the pain would have been marginal or just a feeling and they would have ignored it. They would go on to break the spine and be gobbled up.
In other individuals the pain would have been sufficiently strong to stop them lifting or bending. Even if they suffered further pain they would survive. The more severe the pain was, the more that these individuals would stop doing anything that might further damage the spine.
This Is the ‘Evolution of Low Back Pain’. It has evolved to be an amazingly severe and persistent pain. It is also a very successful warning pain. Real damage is relatively rare and only develops progressively.
We all know that many joints and structures of the spine become involved and are eventually damaged when a low back problem has started. This makes it difficult to analyse the real cause of the problem. Many causes and components have been proposed.
Do the known statistics of the problem support the cause proposed here?
The only clear statistical association is with driving cars. This was first shown by Kelsey and Hardy in 1970 and has been confirmed by many studies since. Would we expect this mechanically? The answer is definitely yes. Car seats tip the thighs and therefore the pelvis further back than almost any other seat. Car seats incorporate far more direct support for the lumbar spine than any other seats. We sit still in a car seat for far longer than we ever sit anywhere else. This mechanical situation could not be better designed to cause the problem outlined above.
If we combine Kelsey and Hardy's work with the surveys by Mark Porter, Professor of Ergonomics at Loughborough University UK it appears that a high mileage car driver is about twelve times as likely to have a serious low back problem as anyone who never uses a car at all. (This work was published in the trade magazine Automotive Interiors International )
This combination may not be good statistics but it's very good common sense. It suggests a far higher correlation between driving cars and low back pain than between smoking and lung cancer. Comparison of these two surveys also suggests that the situation is far worse for the high mileage driver in the late nineties than it was in the late sixties. Is this compatible with the mechanical argument proposed?
Yes. It is more than compatible. It's predictable. In the eighties and nineties the angle of the sitting surface of car seats was tilted further backwards in order to counter the problem of slipping under the seat belt in an accident. At the same time lumbar support was introduced generally into car seats. The combination of these two is bound to increase the flexion force in the spine at the lowest spinal joints. We should expect the statistical situation to be worse and judging by these published statistics it is.
What can we do about this problem before it results in serious damage to the spine? We need to find some way of limiting the flexion of the lowest two discs to the designed or evolved shape defined above. Our civilised lifestyle causes the problem so obviously modifications of this are one part of the solution. This is what Natural Joint Mobility is all about and obviously backrests must incorporate pelvic support not lumbar support.
But even with this knowledge of what we need to do, it can be a slow process to correct the distortions caused by a lifetime of civilised sitting. People want, and deserve, a more instant and complete solution.
One of the medical procedures currently used is sclerosing injections into the ligaments at this level to reduce the mobility. In principle this will help but the ligaments are not suitably oriented. There is no supraspinous ligament at these joints. It stops at L4 (Rissanen). We could however build up a supra-spinous ligament from the spinous process of L4 to some points on the sacrum. This should be nylon or carbon fibre so that it does not simply stretch plastically under the flexion forces defined above.
This solution is a simple and obvious result of being able to define exactly how far these discs (L4/5 and L5/S.) should flex. It might turn out to be a very effective corrective measure in the early stages of a low back problem. I am interested in working with an orthopaedic surgeon who wishes first of all to fully understand this proposal and then to develop his or her own method of implementing it. (Click here for
This is explained in more detail in the booklet;
by John Gorman.
Member of the Institution of Mechanical Engineers
Member of the Institution of Electrical Engineers