There are three predisposing factors in the etiology of low back pain that overshadow most others. The first and most important factor is the sitting posture. A good sitting posture maintains the spinal curves normally present in the erect standing position. Postures which reduce or accentuate the normal curves enough to place the ligamentous structures under full stretch will eventually be productive of pain. Such postures are referred to as poor sitting postures.
A poor sitting posture may produce back pain in itself without any additional other strains of living. We have all seen patients who entered an airliner, a car, or even a common lounge chair in a perfectly healthy and painfree state only to emerge hours later crippled with pain and unable to walk upright. Alternatively, a poor sitting posture will frequently enhance and always perpetuate the problems in patients suffering from low back pain. By far the great majority of patients complain of an increase in pain white sitting or on rising from sitting. On examination of thousands of patients, many of them in Europe and North America, the same picture emerges: those people who are developing low back pain problems nearly always have a poor sitting posture.
As Wyke has said, once a person has been sitting in a chair for more than a few minutes the lumbar spine assumes the fully flexed position. In this position the musculature is relaxed and the weight bearing strains are absorbed by the ligamentous structures. Try the following experiment yourself: sit relaxed in any chair and think of nothing in particular; after ten minutes deliberately try to produce more flexion in the low back; very little will happen. Without you realising it your spine has fallen into full flexion. Relaxed sitting for any length of time places the lumbar spine in a fully stretched position. This will become painful, if maintained for a prolonged period.
By sitting in this manner we are repeatedly doing to our low back something we would not permit to happen in any extremity joint. We do not hold our wrist, ankle, knee or shoulder in a fully stretched position until or after it has become painful. Instead, when the stress exceeds a certain limit the position of the limb is automatically changed from the fully stretched position. A similar but less effective mechanism applies to the low back in silting: when pain arises while sitting we merely change from one position of full stretch to another. In general, relaxed sitting tends to become a poor sitting posture. It is difficult to avoid stress on the lumbar spine in relaxed sitting unless special instructions are followed. There is little hope of curing low back pain as long as our patients are permitted to sit incorrectly.
Andersson et al, have demonstrated how in sitting the intradiscal pressure increases as the spine moves into kyphosis, and decreases as it moves into lordosis. Clinically, patients often describe that during sitting their pain increases with movement towards kyphosis and decreases with movement towards lordosis. In these instances there is a correlation between intradiscal pressure and pain patterns which may well incriminate the intervertebral disc as being responsible for, or at least contributing to, the production of low back pain.
Environmental factors may contribute greatly to the etiology of low back pain due to sitting. Working platforms which are not adjusted to individual requirements, and poorly designed seating for domestic, commercial and transportation purposes will promote poor sitting postures. Expensive anthropometric and ergonomic studies, aimed at improving office furniture, have failed to produce the desired result in respect of adequate support and comfort for the low back. A re-design of furniture may be necessary, based on the concepts of efficient working positions in sitting. Unless pressure can be brought to bear on manufacturers of seating furniture, poorly designed chairs will continue to add to the misery of patients with low back pain. In the meantime we should educate our young and re-educate the rest of the community regarding the correct sitting posture, for even the best designed chairs will be used incorrectly unless the user understands what is the correct position.
Postural factors other than sitting may predispose to low back pain. Some sleeping positions and work-related postures may be potentially damaging and will under certain circumstances cause or perpetuate low back pain. Such factors are not discussed here. However, they should be kept in mind and dealt with individually as they present themselves.
Loss of extension range
The second factor predisposing to the production of low back pain and its recurrence is the loss of lumbar extension. Studies in 197212 and 197910 indicated that respectively seventy-five and eighty-six percent of patients with low back pain had a loss of extension. A reduced range of extension influences the posture in sitting, standing and walking.
As a result of poor postural habits especially in affluent societies man gradually loses the ability to perform certain movements. From postural causes alone the lumbar spine undergoes adaptive changes and from my own observations it appears that few adults reach thirty years of age and maintain normal extension movements. The loss is reversible (with effort) up to fifty or sixty years of age in many patients.
If low back pain has been evident in the patients previous history, there is nearly always some modest restriction of lumbar extension which will improve if the appropriate exercising is commenced. I believe in these patients the loss of extension is caused by bad posture or lack of adequate movement at the time that repair mechanisms were operative. As healing occurs, adaptive shortening of scar tissue prevents movement and unless the patient is adequately advised, the scarring will form with the spine held in the slightly flexed relaxed position, for few patients rest with the spine extended. Again it is the movement towards extension that remains limited.
A reduced range of extension acquired in either manner described, rarely recovers spontaneously to the full. Unless the patient takes specific measures to regain it, extension remains reduced and the ability to sit with a lordosis is impaired or lost. It is not generally recognised that it is impossible to sit and maintain a lordosis without an adequate extension range. Patients who, for some reason or other, have to sit with a flattened lumbar spine, are condemned to sit with a raised intradiscal pressure as well as a taut posterior annular wall.
Reduced extension is not only an impediment to the adoption of good sitting postures, it is also a major obstruction to obtaining the fully upright posture in standing. A reduced extension range will produce full stretch positions prematurely during prolonged and relaxed standing, and once sufficient stress is present, pain will arise.
As the loss of extension increases, the patient will be forced to walk slightly stooped. The maintenance of the slightly flexed posture creates a constant stress on the nucleus and posterior annular wall. Under normal circumstances this stress is relieved by moving into extension. However, as extension is no longer possible lasting relief cannot be obtained. Eventually adaptive changes will extend to all periarticular structures including the apophyseal joints.
Frequency of flexion
The third predisposing factor to low back pain is the frequency of flexion. When one examines the lifestyle of western cultures in the twentieth century, it is not hard to understand why man is losing his ability to freely extend the spine. He wakes in the morning, stoops over a wash basin and sits to have breakfast; all so far in flexion. He then travels to work by bus, train or car; he works bent forwards either in sitting or in standing; almost the whole day is spent in flexion. He sits travelling home, and again for his meal; then he may work in the garden or watch television for the evening, remaining flexed for most of the time. He sleeps in a flexed position nearly the whole night, awaking the next morning to repeat the cycle. It can safely be claimed that the spine is constantly being flexed to the maximum, but is rarely extended to the maximum.
When evaluating these predisposing factors it appears beneficial to recommend that patients with low back pain should extend the lumbar spine from time to time and under certain circumstances yet to be defined. This will theoretically reduce the stress on the posterior annular wall and simultaneously cause the fluid nucleus to move anteriorly — that is, away from the site of most protrusions and extrusions. Moreover, patients should sit with the lumbar spine supported in some extension as in this position the intradiscal pressure is reduced.” The sensible use of extension to overcome the disadvantages of prolonged flexion seems to be a simple and logical step towards reducing some of the predisposing factors involved in low back pain and its recurrence. Here we have the beginning of a prophylactic concept.
Insufficient understanding of the mechanics involved in the production of low back pain has led some people to condemn extension of the spine and those who advocate it. If a Higher Authority had decided that extension is undesirable or harmful, the facet joints in the spine would have been placed accordingly! In the absence of such an indication it appears impertinent for man to place such restrictions on the use of the human frame, which after all has evolved over millions of years to become the wonderful, dynamic, mechanically bewildering and self-repairing marvel that it is. It managed to do this, I must add, without the benefits of medical specialisation.
The predisposing factors for low back pain and its recurrence are mostly related to positions and the short and long term consequences of maintaining them. Movement and activity may precipitate low back pain and therefore contribute to its incidence and recurrence.
It is often the unexpected and unguarded movement that causes a sudden episode of low back pain. This may occur during work related activities, be it domestic or occupational, and in sports and recreational activities — for example, squash, tennis, golf, football and gymnastics. Whatever the situation, when any of the predisposing factors are present very little is required to precipitate a sudden onset of low back pain, and the exciting strain may be an event as trivial as stooping momentarily. When attempting to reduce the frequency of low back pain episodes, it is necessary to examine and advise each patient individually regarding the precipitating circumstances involved in his particular case.
Lifting produces a strain which is often a precipitating factor, especially when heavy, prolonged and repeated lifting are involved. The risks of incurring low back pain are greater when the weight of the load to be lifted increases, and when lifting is performed by untrained and unfit people.
Nachemson16 describes the effects on the intradiscal pressure when certain positions are adopted while weights are held in the hands. Lifting from the forward bent position is one of the most stressful activities: when a certain weight is lifted with the back bent and the knees straight, the intradiscal pressure rises up to five times compared with that present when standing erect; however, when the same weight is lifted with the back straight and the knees bent there is a marked reduction in intradiscal pressure.
The coach of the Canadian Olympic weight lifting team explained to me that his team members were instructed to lift with a hollow in the low back. This he said prevented low back problems among the weight lifting fraternity.
Correct lifting techniques do have an effect on pain brought about by lifting. The more the lordosis is maintained while lifting, the less discomfort will be experienced. When appropriate, correct lifting should be taught as a prophylactic measure.