Intervertebral disc prosthesis. Results and prospects for the year 2000.

Presently, the kinematic disc prosthesis model (SB Charité) is the best disc replacement compromise, and is the basis of the evolution of the prosthetic concept at the dawning of the year 2000. Clinical results of a homogeneous series of 105 cases with a mean followup of 51 months show 79% of the patients had an excellent result and 87% returned to work, radiologically, these results correlated with restoration of a well balanced lordosis and with segmental mobility. Factors leading to failure are posterior facet arthritis, osteoporosis, structural deformities, and secondary facet pain. Two- and 3-dimensional numeric modeling enables one to study the total facet joint loading and the maximal local loading on the facet. Dissociation of the stiffness in pure rotation and stiffness in translation of the disc are the bases of the technologic improvement.