The fibrous disc that acts as a cushion between the bony vertebrae (see SPINAL COLUMN), enabling them to rotate and bend one on another. The disc tends to degenerate with age and may get ruptured and displaced – prolapsed or slipped disc – as a result of sudden strenuous action. Prolapsed disc occurs mainly in the lower back; it is more common in men than in women, and in the 30–40 age group.