It can be hard to pinpoint the cause of a person’s low back pain. It is more common for a patient to be unaware of what has caused their back pain, than to be able to blame it on a specific trigger. Sometimes it is obvious such as ‘I fell on to my buttocks’, or ‘I went to lift my child, and my back just went’, but more often patients cannot explain how it started.
The spine can accumulate dangerous amounts of load for prolonged spells quite painlessly, until the threshold is reached where tissues become injured, whilst ‘doing nothing’ or following a trivial event. Of the three basic mechanisms which cause back injury this scenario is the most common.
97% of low back pain is ‘mechanical’ (Deyo and Weinstein, 2001), that is arising from injury to muscles, ligaments, joints and occasionally nerves in the low back (this 97% includes therefore the ‘Simple Backache’ and ‘Nerve Root pain’ categories). Essentially mechanical injury to the low back can occur in one of three ways or a combination thereof.
METHODS OF INJURY
Tissue (muscles, ligaments and discs) can, of course become injured by a single overloading event such as a trauma. In the example below the skier’s low back tissues can safely tolerate smaller impacts as he pounds over bumps, but a huge abrupt load to the spine as in a hard fall can be sufficient to overload the muscles and ligaments causing tearing, and inflammation.
A second way tissues can become overloaded is through a repetitive loading, especially when performed in postures which allow forces to focus in the lumbar spine. In this example below the worker’s spine can happily tolerate numerous lifts within a short space of time, but with each lift a gradual ‘stretching’ of the muscles, ligaments and discs means that with the nth lift the tissue becomes torn resulting in injury. Interestingly, if she were to have stopped some lifts prior to the one that caused the injury, and taken a break for several minutes, the recovery of the muscles and ligaments would have allowed her to carry on safely.
A third basic method to injure the low back is to put the spine under a constant load and maintain that load statically. Working in a sustained forward bent posture creates a gradual deformation of the low back muscles, ligaments and discs, which will, unless they reverse this posture in time, cause injury. Another example of this method would be to sit in a slouched posture for too long.
Francois Hacault BSc, DC
01727 848 481