Mechanical factors in the etiology of low back pain.

Mechanical experiments were performed on cadaveric lumbar intervertebral joints in order to outline the etiology of common back injuries and low back pain. The results suggest that the osteo-ligamentous lumbar spine is most at risk in the lordotic posture and when bending forward. Sustained lordotic posture can produce abnormal loading of the apophyseal joints. Bending forward wedges the lumbar discs, rendering them vulnerable to fatigue injuries if heavy labor is performed in this posture. Excessive flexion at some spinal level will cause posterior ligament damage, and a strong contraction of the back muscles can then cause prolapsed intervertebral disc. Key words: Lumbar spine, lordotic posture, prolapsed disc.