As children we have the great gift of a mobile, strong, well designed and painless spine and it is unusual for stiffness to be an issue as the lumbar spine has evolved to do the job of weight bearing and providing movement. Intervertebral discs separate the spinal vertebrae, allowing more movement in areas where they are thicker and also coping with variable loads. The posterior spinal facet joints limit and control segmental movement, preventing the spine from displacing inappropriately under the shear forces. Strong, balanced and coordinated muscle actions complete the picture.

Inhibition of the stabilising musculature occurs with an episode of acute spinal pain and this can persist beyond the resolution of the pain to generate a long-lasting instability which puts the segment at increased risk of re-injury over time. Longer term effects include the occurrence of degenerative alterations in the spinal structures such as joints and discs, causing segmental levels to develop stiffness and eventually chronic back pain. The discs have fluid forced out of them by gravitational compression forces and must counteract them by generating a fluid absorption force.

If over time the compressive force gets the upper hand, the disc loses some of its hydration and eventually narrows. Narrowing can be seen on x-ray but the disc can start to become troublesome before it is changed enough to show up on the x-ray. In the spine two vertebrae and the intervening disc are known as a segment and it is the segments with altered discs which become stiff, preventing normal movement and forcing anatomical structures to take abnormal loads in abnormal positions. The vertebra above a stiff segment is unable to participate in normal movement and this stiffness can be felt by a physiotherapist.

Muscle spasms are a typical reaction to an acute injury and has a protective function, stopping the damaged segment from moving while it is so inflamed and thereby giving it some freedom to heal. As the pain settles and the injury heals the back spasms should gradually settle and allow normal movement to be restored. Unfortunately this does not always happen, with some muscles remaining over protective and eventually forming a contracture, an abnormally shortened tissue structure which maintains an abnormal joint position.

Increase of the compression forces through the spine can be promoted by sitting for long periods, leading to increase in the fluid loss from the discs. Discs rely on us repeatedly bending forwards for disc health and nutrition and avoidance of this movement compromises disc wellbeing, leading to an increased potential risk of degenerative change. A weakness in the abdominal muscles and the development of abnormal postures also contribute to these problems.

A typical history is to have an episode of severe low back pain which gradually develops into a segmental stiffness problem. The stiff areas may be present asymptomatically for many years in many individual areas of the spine before one of them develops into a painful segment which causes restriction. Sitting for a long time or spending time bent into flexion will tend to aggravate this condition once established as joints are moved beyond their comfortable limits. The lumbar facet joints become fixed into extension and the whole segment suffers from adaptive shortening, forfeiting its ability to move normally. I have back problems very like this and it can be quite difficult, forcing me to limit heavy or repetitive work or any significant time in flexion.

Sarah Key, a physiotherapist who is well known in the UK, has produced the Sarah Key's Back Sufferers Bible, a book in which she sets out her views of what is going on in this most common of musculoskeletal syndromes. She does acknowledge that it is hard to bring solid evidence for many of her interpretations but seems to have many good and practical therapy ideas to approach the back pain problem with. She covers the main syndromes which typically occur, giving treatment routines for self management of each one, all of which I have found very useful for my own lower back pain. Now I have something I can do about it rather than accept it as a fact of life.