Fatigue characteristics of posterior elements of vertebrae.

The fatigue strength of vertebral posterior elements was determined by applying repetitive forces to the inferior joints between the articular processes of human rhesus-monkey vertebrae. The results indicate that in vivo stresses resulting from unusual activities for sustained periods can induce fatigue fracture of the lumbar vertebrae. Comparison of these data with those of other investigators suggests the use of ultimate strength as a normalizing factor to correlate fatigue-strength data obtained under different test conditions.