TOWARDS A BETTER UNDERSTANDING OF LOW-BACK PAIN: A REVIEW OF THE MECHANICS OF THE LUMBAR DISC

Abstract

SUMMARY 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 measure- ments of disc pressure have demonstrated how the load on the lumbar disc varies according to the position of the subjectl'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.