The Degenerative Cascade

Many of the problems that affect the lower back result from a wear and tear process called degenerative change.

It is important to emphasise that these changes often occur as part of the natural ageing process that affects us all. In many cases they cause no symptoms at all, or no more than very mild occasional back ache or stiffness. Unfortunately, some individuals are affected more severely by these. This section looks at how these changes develop and the problems that may occur.

One of the first changes to affect the intervertebral disc is a gradual breakdown of the material which makes up the central nucleus. This may cause the disc to become a little soft and 'wobbly' much like a tyre which has had some of its air let out. This can lead to a sense of vulnerability in the back which is due to abnormal movement between the vertebrae. Somebody affected by this problem will lean or bend forwards slightly and their back will 'go' suddenly and very painfully. This is referred to as instability and forms the basis for some surgical procedures which aim to restore stability.

In much the same way that driving on a flat tyre will gradually damage the tyre itself, the abnormal movement resulting from a softened disc in the early stages of degenerative change can cause tears and other damage to the disc and facet joints. The wall of the disc can become weakened, bulging out into the spinal canal. The extra stress on the facet joints can lead to arthritic changes occurring here too. These arthritic changes can be painful and, as they become overgrown, the enlarged facet joints can affect the space available for the nerves in the spinal canal.

As the damage progresses the disc will gradually collapse, becoming narrower. The load through the disc, normally spread out evenly, becomes 'lumpy' with painful areas of high stress. The shock absorption capacity of the disc is reduced. The openings for the nerves leaving the spine, the neural foramen, become narrowed, leading to nerve root compression. As the disc collapses it tends to overload the facet joints even more, so arthritic changes of these joints may get worse. The joints may erode, allowing one vertebrae to start to slip forwards on top of the other, further squeezing the space for the spinal nerves. This degenerative cascade can cause various clinical problems.

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