Fatigue fracture of human lumbar vertebrae.

Fatigue fracture of human lumbar vertebrae under cyclic axial compressive load has been investigated in vitro for load magnitudes between 20% and 70% of the ultimate compressive strength and cycle numbers between 1 and 5000. In addition, the dependence of the ultimate compressive strength of lumbar vertebrae on trabecular bone density and geometric dimensions was investigated. Seventy specimens of human lumbar motion segments were subjected to a fatigue test; 35 specimens were subjected to an ultimate strength test. The results state the probability of a lumbar vertebra encountering a fatigue fracture in relation to the magnitude of the cyclic load and the number of load cycles. In addition, it is shown that the ultimate compressive strength of a vertebra can be predicted with an error of less than 1 kN on the basis of bone density and endplate area.