New technologies in spine: nucleus replacement.

Nucleus replacement offers several benefits over other surgical options. Several design criteria need to be met. Nucleus prostheses can be either preformed or formed in situ. Preclinical evaluations should include biomechanical testing, biocompatibility testing, and surgical technique evaluation. Indications and contraindications of nucleus prosthesis are largely determined by the benefit-to-risk ratio and benefit-to-cost ratio.