Fatigue failure at the disc-vertebra interface during cyclic axial compression of cadaveric specimens.

Seven specimens of adjacent lumbar vertebrae, with the disc between them, were obtained from five cadavers (age 40-80 years). The vertebrae were bisected in the transverse plane, posterior elements were removed and the specimens subjected to cyclic compression, with a peak load of 1.9 kN at a frequency of 0.5 Hz. During loading, the bulging of the end-plate into the more caudal of the two vertebrae was monitored using a displacement transducer. Application of the load was continued for 7000 cycles, or until the end-plate displacement reached 1.5 mm, whichever happened first. One specimen did not fail; another failed within only five loading cycles, i.e. not by fatigue. The remaining five specimens showed signs of fatigue failure but the end-plate remained intact.