Requirements for an artificial intervertebral disc

Intervertebral disc degeneration is an important social and economic proble m. Presently available artificial intervertebral discs (AIDs) are insuffici ent and the main surgical intervention is still spinal fusion. The objectiv e of the present study is to present a list of requirements for the develop ment of an AID which could replace the human lumbar intervertebral disc and restore its function. The list addresses geometry, stiffness, range of mot ion, strength, facet joint function, center of rotation, fixation, failsafe ty and implantation technique. Date are obtained from the literature, quant ified where possible and checked for consistency Existing AIDs are evaluate d according to the presented list of requirements. Endplate size is a weak point in existing AIDs. These should be large and fit vertebral bodies to p revent migration. Disc height and wedge angle should be restored unless thi s would overstretch ligaments. Finally, stiffness and range of motion in al l directions should equal those of the healthy disc, except for the axial r otation to relieve the facet joints.