Wear of the Charité® lumbar intervertebral disc replacement investigated using an electro-mechanical spine simulator

The Charitelumbar intervertebral disc replacement was subjected to wear testing in an electro-mechanical spine simu- lator. Sinusoidally varying compression (0.6-2kN, frequency 2Hz), rotation (62, frequency 1Hz), flexion-extension (6 to 23, frequency 1Hz) and lateral bending (62, frequency 1Hz) were applied out of phase to specimens immersed in diluted calf serum at 37 C. The mass of the ultra-high-molecular weight polyethylene component of the device was measured at intervals of 0.5, 1, 2, 3, 4 and 5 million cycles; its volume was also measured by micro-computed tomogra- phy. Total mass and volume losses were 60.3 6 4.6mg (mean 6 standard deviation) and 64.6 6 6.0mm 3 . Corresponding wear rates were 12.0 6 1.4mg per million cycles and 12.8 6 1.2mm 3 per million cycles; the rate of loss of volume corresponds to a mass loss of 11.9 6 1.1mg per million cycles, that is, the two sets of measurements of wear agree closely. Wear rates also agree closely with measurements made in another laboratory using the same protocol but using a conventional mechanical spine simulator.