Towards a better understanding of low-back pain: a review of the mechanics of the lumbar disc.

Abstract

By measurement of intradiscal pressure in vitro, the hydrostatic properties of the nucleus pulposus of normal lumbar intervertebral disc was established. The stress distribution within normal discs subjected to vertical load was also explained, demonstrating the high tangential strains occurring in the posterior part of the annulus fibrosus. Intravitally performed measurements of disc pressure have demonstrated how the load on the lumbar disc varies according to the position of the subject's body. Compared to the pressure or load in the upright standing position, reclining reduces the pressure by 70%, while unsupported sitting increases the load by 40% and forward leaning and weight lifting by more than 100%. Similar relatively large augmentations of the load were observed in subjects performing various commonly used muscle-strengthening exercises. Measurement of intradiscal pressure is instrumental in explaining, from a mechanical point, the occurrence of posterior ruptures in the lumbar discs, and provides a basis for the rational treatment of patients with low-back pain in so far as these exhibit increase of pain on increased mechanical loads. For the majority of patients with low-back pain, the cause is unknown, although most evidence so far presented links the lumbar intervertebral disc to the pain syndromes. Results of recent studies have shown that both chemical and mechanical factors are probably of importance. So far we cannot successfully treat the chemical part of the disc syndrome. Since all our patients exhibit more pain when the spine is mechanically loaded, knowledge gained from intravital disc-pressure measurements provides a basis for successfully treating the mechanical part of the condition. Since none of the frequently prescribed and more spectacular remedies has ever been proved statistically superior to any of the others, it is most fair to our patients and to ourselves to use simpler, less expensive, and less dangerous programmes, such as bed-rest, administration of salicylates, and proper ergonomic advice. Based on a scientific approach, the low-back-pain school is intended to help the patient to be able to cope with these back troubles, to avoid excess therapy, and to decrease the cost both for the individual and for Society.