Figure 6: (A),(B) The distribution of vertically acting compressive ‘‘stress’’ measured along the sagittal mid-plane of a 46-year-old cadaveric lumbar intervertebral disc (anterior on right). Compressive damage to the vertebral body (lower) reduces the pressure in the nucleus, and generates high stress peaks in the annulus. This disc was subjected to a compressive force of 2 kN during the ‘‘stress’’ measurements. (C) Load sharing in the lumbar spine is affected by intervertebral disc degeneration. When the disc is normal (left), the neural arch resists only 8% of the applied compressive force, and the remainder is distributed fairly evenly between the anterior and posterior halves of the vertebral body. However, severe disc degeneration (right) causes the neural arch to resist 40% of the applied compressive force, whereas the anterior vertebral body resists only 19%. Data from cadaveric lumbar motion segments loaded at 2 kN in the simulated erect standing posture following a period of compressive creep loading [69].