The strength in anterior bending of lumbar intervertebral discs

Abstract

Study design: This was a motion segment experiment.

Objectives: To determine the strength in bending of lumbar intervertebral discs.

Methods: Eighteen "motion segments" consisting of two vertebrae and the intervening disc and ligaments were loaded to simulate forward bending movements in life. The range of flexion and the resistance to bending of each specimen was compared before and after removal of the posterior elements. Nine of the discs were tested after the intradiscal pressure had been reduced by damaging the vertebral end plate in compression.

Results: The posterior elements restricted the disc to 80% of its full range of flexion. The strength in anterior bending of isolated discs decreased with age and was 33 Nm on average. Reducing intradiscal pressure did not affect the discs' strength in bending.

Conclusions: Disc failure in bending occurs through overstretching of the outer anulus in the vertical direction. In life, the posterior elements may not adequately protect the posterior anulus from fatigue damage.