Risk Factors

Since it has been shown that back pain is not always caused by an organic disorder of the spine, the factors associated with a greater risk of pain are now being studied. One must be careful when interpreting these studies, which show that people who have back pain also present certain characteristics more frequently than those who do not have pain. That means that these factors are associated with a greater risk, not necessarily that they are the only cause of the pain or that eliminating them will make it better.

Despite this limitation, rigorous epidemiological studies do exist revealing the factors associated with a greater risk of back pain. And they should be considered, especially those cases in which one can detect the mechanism which might explain its possible influence. Some of the factors that have been studied the most are

- Repeated flexion-extension is associated with a greater risk of back pain.

When we bend our backs, increased pressure is produced inside of the intervertebral disc. If at the same time we are lifting a weight and straighten our back, the pressure on the posterior part of the disc increases so much that it can fracture or break, producing a disc hernia. That process may occur at one time, if the strain is intense, but it tends to be produced by a mechanism of accumulation: each inappropriate bend increases the impact of the nucleus pulposus on the fibrous disc covering and erodes it until fracturing or splitting it.

In addition to the disc, the back muscles are also strained when bent forward. This posture can be maintained thanks, essentially, to the controlled tension of the paravertebral, gluteus and iliocostalis muscles which prevent the body from falling forward. The greater the angle of flexion, the greater the effort required by the lower back muscles and the fewer number of segments that make it, thereby facilitating strain and overloading.
Mechanical studies show that disc and muscle overloading is greater if one bends with straight legs and less if bending at the knees, using the legs, and the back is maintained straight.
In fact, epidemiological studies show that back pain is more frequent among those people who make repeated flexion-extension movements of the back, especially if they do so lifting, and if the weight is excessive or the muscle strength insufficient

- Frequent twisting and rotating the spine is associated with a greater risk of back pain. Because of the shape of the vertebras, the cervical spine (neck area) can turn more than the thoracic (central back) and the thoracic more than the lumber (low back). The repetition of exaggerated twists and turns of the low back can strain the facet joint and muscles and even the disc, especially if done when lifting or carrying weight.

- Exertion and strain; is associated with a greater risk of back pain. This association may be caused by a mechanism of overloading and strain and may be associated with a greater risk if the exertion is made while bending or twisting:

A very intense exertion can cause back pain. If the muscles are very strong, they are injured before the intervertebral disc. In that case, the pain caused by the muscle injury-painful, but harmless and tends to heal itself in a few days-stops the effort and protects the disc. If the muscles are not strong enough, the intervertebral disc may be injured instead of the muscles.

Continuous repetition of exertion, even though it may not be exceedingly intense, may cause back pain, possibly because of the accumulation of small injuries in the intervertebral disc or the facet joint, or more commonly because of the repeated strain of the back muscles.

Over-exertion does not always involve lifting or carrying weight: poor posture can strain the muscles or the spinal structure. If the incorrect postures are maintained over a long enough time or are repeated frequently they can cause back pain due to a straining mechanism, even though no weight has been lifted or carried.

It is true that an especially intense over-exertion made without bearing in mind the norms of good posture, especially if made while bending, can lead to an episode of pain. However, just because this process is typical does not mean that it is common. It is much more common that episodes of back pain appear without having been provoked by exertion.

Epidemiological studies show that back pain is more frequent among those people who carry out intense and repeated exertion, especially if they do so while bending, turning or twisting the spine, or when muscles strength is insufficient.

- Vibration; is associated with a greater risk of back pain. Epidemiological studies show that being subjected to vibrations affecting the entire body increases the risk of back pain. This is the case, for example of tractor drivers and other people who handle similar machinery. It is likely that the vibration provokes pain as a result of one of these mechanisms:

Vibration entails a rapid shortening and lengthening of the muscles, so that it may produce muscle contraction.

Vibration increases the strain on the intervertebral disc and facet joint cyclically and rapidly.

Vibration is a direct cause for the activation of the pain nerves in the spinal ganglia.

- Lack of strength, resistance and conditioning of the back muscles; is associated with a greater risk of back pain and its recurrence, as well as possibility that it may become chronic. Studies confirm that back pain appears more readily and lasts longer in persons who do not have strong, resistant and conditioned muscles. This fact is most likely explained by various mechanisms:

If the muscles are strong and well balanced, the distribution of the load is correct and lowers the risk of muscle contractions or strains.

The greater the muscle strength and resistance, the greater the structural resistance to the load.

In normal conditions, pain appears in the muscles before the other back structures, so that it alerts us to a possible injury. If the muscles are not very strong, this mechanism does not function effectively.

Under normal conditions, our muscles inform us of our position in space. When our muscles are insufficiently developed, that source of information is defective, so we may adopt incorrect postures without being aware of it.

- Discomfort while lying in bed; is associated with a greater risk of back pain. Studies show that back pain is more common among those people who feel discomfort in bed or on getting up.

In some studies, discomfort in bed has been associated with a 1800% greater risk of back pain, both among adolescents and adults, while most of the other factors studied (such as gender or physical exertion on the job or in leisure) have been associated with a much lesser effect. Furthermore, scientific studies have also shown that among those people who already suffer back pain, the firmness of the mattress influences the evolution of their pain, so that a medium firm mattress is recommended over a very firm mattress. These data suggest that the characteristics of the bed surface represent an important factor in regard to the existence or evolution of back pain.

It is possible that that influence is due to several factors. If the characteristics of the bed lead to incorrect postures while lying down, the distribution of weight load may be altered, affecting the muscles (either by producing an overload or simply by making it difficult for them to relax) or increasing the strain on the intervertebral discs and facet joint. Given that this factor occurs repeatedly and over a long period of time (it is estimated that a person spends approximately one third of his or her life in bed), over a mid to long range, sleeping on an inadequate bed could end up producing back disorders.

- Having suffered previous episodes of back pain; is associated with a greater risk of future back pain. Scientific studies show that once a patient has had an episode of back pain, it is likely that he or she will have others in the future. Some of the recommendations based on scientific evidence establish that in most patients pain crises are repeated every once and a while without that necessarily meaning that they are getting worse or that they have injured their back again. This fact can be explained for several reasons:

Those people who suffer a crisis tend to have one or several risk factors associated with their lifestyles or personal characteristics. Unless they adopt specific measures, which is not always easy-change of habits, exercise, etc-it is likely that these risk factors will continue to give rise to new episodes.

Studies show that back pain causes muscle contraction by means of a neurological mechanism, and that the muscle receives less blood flow when it is contracted. That can help it to contract again in the future and provoke new pain crises, especially if one stays in bed during the pain episode or after it. Conversely, maintaining the highest degree of physical activity possible (both when there is pain and when there is not) improves muscle condition, reduces the risk of back pain and in the case of existing back pain, improves its evolution.

Studies also show that if back pain limits activity during a certain time, the muscles atrophy easily. Muscle atrophy can make the spine more vulnerable and make it harder to adopt correct postures, which in turn may increase the risk of suffering new episodes of pain.

A neurological mechanism explains that if the cells that perceive pain in the medulla and the brain are activated over a certain amount of time, they are more easily activated in the future, so that even small stimuli may provoke new pain. In fact, if they are activated for long enough, they tend to remain activated even though the painful stimulus that activated them in the first place disappears. In this case, the pain persists even though its initial cause has disappeared.

- Attitude towards pain; influences the risk of pain and above all its duration and recurrence. Available studies reveal that patients who have suffered back pain may react in two different ways:

- Some, (the "avoiders") are afraid of the pain and worry about their future, mistakenly believing that each time they feel discomfort in the back, it means that their injury is getting worse. For that reason, they rest a lot; they avoid physical activity and wait passively for the pain to get better. And they tend to abuse medication, especially pain relievers-.

- Others (the "confronters") are not afraid of the future and have faith that the pain is going to improve, and that if it doesn't, they will be able to adapt to it. They lead as normal a life as they can; they stay active and go to work, avoiding only those activities that the pain really does prevent them from doing. And they are not frightened when they sometimes feel a passing discomfort.

Available studies show that in comparison to the "avoiders", the "confronters" have less risk of a recurrence of pain and if new episodes do appear, they are shorter.

These facts can be explained by various reasons:

- In the first place, for psychological reasons: the "avoiders" tend to become obsessed about their pain and to interpret the passing discomfort they might feel at any given moment as a serious injury. For this reason they feel greater stress, which in turn means an addition risk for their back. In addition, they feel anxious and become depressed with greater facility, which makes them tend to magnify the pain they feel even more.

- Additionally, from the physical point of view, excess bed rest and lack of activity tend to accelerate the loss of muscle strength and resistance, making the back more vulnerable to strain and increasing the risk that the pain will reappear or last longer.

- Stress; increases the risk of back pain. In fact, stress has greater influence on the perception of pain than on the risk of it appearing; that is to say, more than increasing the likelihood of back pain, stress makes one feel the pain more intensely. Probably a double mechanism is produced:

Stress may alter the perception of pain, increasing it.

Some data suggest that stress may provoke an increase in muscle tone and facilitate contractions, though the studies comparing the electrical activity of the muscle in patients with stress and in those without have offered contradictory results.

- Dissatisfaction; increases the risk of back pain and especially the risk of prolonged pain episodes. Studies made in occupational settings reflect that job dissatisfaction increases the risk of back pain and the length of sick leave. From a medical point of view, and apart from occupational considerations, the mechanism that may explain its influence could be two-fold:

A mechanism similar to that of stress.

The unconscious somatization of dissatisfaction with life in the form of back pain.

- Some personality types may influence the risk of back pain and above all the risk of its becoming chronic, as a result of limiting activities. Some studies suggest the existence of certain psychological traits in patients with chronic back pain, distinguishable from those of patients with other chronic disorders. These personality types may facilitate somatization or an obsession with the back pain, which ends up becoming the center of the patient's life. While the research methods used in some studies do not permit a clear determination of whether these disorders are the cause or the consequence of the chronic condition, others suggest that that certain personality types can facilitate the perpetuation of the pain.

- Smoking; its effect is doubtful. Though previously studies agreed in indicating that back pain is more common among smokers than non-smokers, for a long time the influence of tobacco was questioned because the mechanism which might explain it was not known. It was attributed to the fact that smokers tend to work in jobs requiring physical effort with greater frequency, since they generally belong to a lower socio-economic class than non-smokers. However, scientific studies have shown that the harmful effect of smoking on the risk of back pain is maintained independently of socio-economic level and researchers try to explain its influence by:

Irrigation of the intervertebral disc. In normal conditions in a healthy individual, the nucleus pulposus does not have irrigation and the fibrous surrounding envelope receives little blood. In the smoker, circulation is worse and could make the irrigation of the fibrous surrounding even worse, which could accelerate its degeneration or facilitate its injury.

Cough. Smokers tend to cough more than non-smokers. Coughing increases pressure on the intervertebral disc and subjects it to vibration, which increases the risk of degeneration or injury.

Muscles. Smokers tend to be in worse physical condition and have fewer and more poorly developed muscles than non-smokers, which could make it easier for them to strain the vertebral structures and provoke back pain.

However, some studies have concluded that there is no clear relation depending on the dose of tobacco. That could suggest that smoking behaves as a "variable of confusion" (that is to say, it has no effect in itself but behaves as an indictor by being associated with other factors which really do increase the risk of back pain), or that the harmful effect of smoking on the back is manifested from a very small dose, without increasing its effect significantly when increasing the dose. In any case, there are many health reasons for not smoking, independently of its association with back pain or not.

- Being overweight; its influence is doubtful. For years it was believed that being overweight meant an increase in the load the spine must support and therefore increased the risk of back pain. However, when studies were made to prove whether this were really true, contradictory results were obtained. While some studies suggest that being overweight can increase slightly the risk of back pain, most rigorous studies show that, as opposed to what was believed before, its effect is not so important. In fact, at present one cannot affirm with certainty that being overweight increases the risk of back pain, and that it has been proven that if it really does have an influence, it is minimal. However, studies exist showing that reducing excess body weight improves health in regard to other disorders, such as cardiovascular or endocrinological illnesses, so that controlling one's weight is worthwhile, though its effect on back illness is at best doubtful.

- Height; its influence is doubtful. All other factors being the same, for years it was thought that back pain was more common in taller people, due to the increased load their height entails. However, epidemiological studies do not confirm this assumption. It is debatable whether height increases the risk of back pain, and if it does, its influence is minimal.

- Prolonged sitting; its effect is doubtful. For many years it was believed that the fact of spending long hours sitting increased in itself the risk of back pain.

Very few studies have been made to evaluate the effect of the characteristics of the chairs one uses on the risk of back pain or its evolution, and the methods of study used prevent one from stating with certainty that these characteristics have a determining effect. However, some studies made with school children suggest that the characteristics of the furniture do influence the risk of back pain and its evolution over a middle range. Thus, data exist suggesting the advisability of using adjustable chairs, which allow correct postures when they should be maintained.

Nevertheless, and independently of whether it is appropriate to use chairs that allow adopting healthy postures, the studies made do not show in any consistent fashion that the number of hours spent sitting signifies in itself a risk of back pain. Nowadays, it is believed that in adults, more than the fact of sitting in itself, what is harmful is the lack of physical activity that tends to be common among sedentary people. Thus, researchers try to explain the possible influence of this factor by a double mechanism:

Prolonged sitting entails the loss of strength in the abdominal and paravertebral muscles, so that small overloading - by exertion or posture -may occur which causes pain.

Maintaining this posture, especially when it is incorrect, increases notably the pressure on the intervertebral disc, which facilitates its deterioration or injury, and may lead to muscle strain.

On the other hand, and while there are no scientific studies on the subject, patients with back pain often tend to say that they suffer more when the weather changes. One explanation could be the variation in atmospheric pressure. Both inside the intervertebral discs (especially if they have deteriorated) as well as in the joints, including the facet joint, there is a vacuum (zero pressure). This vacuum helps the bones to stay together. The drop in atmospheric pressure could cause a suction effect, which could aggravate the possible existing inflammation in the area. That would explain that pain may appear or get worse when the atmospheric pressure diminishes-that is to say, a few hours before the weather changes-.