What Is A Stiff Spinal Segment

In the well-oiled spinal chain, a stiff spinal segment is a sluggish vertebra which participates less willingly than the others in overall spinal movement. More often than not the stiffer one causes no trouble; it just sits there being coaxed along by other more vigorous neighbours—and also being compensated for by them. When the spine performs its usual grand-scale activity, each segment contributes a tiny bit more to make up for the stiffer one doing a little bit less.

Most spines have a patchy distribution of stiff links randomly scattered throughout, from the base of the skull to the sacrum. Some areas of the spine are naturally more mobile than others. The neck, for example, is more freewheeling in all its movements, while the low back is much more a fundamental pillar of support. In other parts of the spine, some movements are generous and others meagre. In the thoracic region, sideways bending is never very expansive because the ribs are in the way, but rotation or twist here is very free.

In the low back, all freedoms are kept to a minimum except forward bending. Most of the anatomical details of this part of the spine are designed to help it perform this single most important role. In a sense

Microtrauma The Spine
Figure 2.1 The disc of a stiff spinal segment is like a hardened washer between its two vertebrae. This makes the upper vertebra stiffer to palpation pressures.

the main function of the low back is to make the skeleton bendable in the middle and therefore adjustable in height. It is then possible to have your hands, eyes, ears and mouth, indeed the 'thinking' part of your body in positions where it can be the most useful.

It is interesting that the least and most mobile lumbar segments are vertically adjacent. The fifth lumbar vertebra (L5) at the bottom of the stack is the least mobile and L4 immediately above is the most. Although L4 can get stiff, it should come as no surprise that this segment most commonly develops over-mobility problems (see Chapter 6, 'The unstable spinal segment') while L5 is the most frequently diagnosed 'stiff spinal segment'.

A less mobile segment becomes an easy target for trauma because it cannot absorb shock as easily as the rest. Its vertebra cannot roll with the punches and is therefore susceptible to strain. An ill-considered move can leave the problem vertebra locked and twisted on its axis, rather like a screw-top lid of a jar locking down when it is twisted home. If severe enough, the tail of the vertebra (the spinous process) can be visibly out of line with the rest. More commonly though, it reveals a reluctance to be pushed transversely one way compared to the other. The pain from this sort of problem is usually felt on one side of the back only, also manifesting as a 'bruised-bone' feeling whenever the vertebra is touched.

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