The development of tissue engineering therapies for the intervertebral disc is challenging due to ambiguities of disease and pain mechanisms in patients, and lack of consensus on preclinical models for safety and efficacy testing. Although the issues associated with model selection for studying orthopedic diseases or treatments have been discussed often, the multifaceted challenges associated with developing intervertebral disc tissue engineering therapies require special discussion. This review covers topics relevant to the clinical translation of tissue-engineered technologies: (1) the unmet clinical need, (2) appropriate models for safety and efficacy testing, (3) the need for standardized model systems, and (4) the translational pathways leading to a clinical trial. For preclinical evaluation of new therapies, we recommend establishing biologic plausibility of efficacy and safety using models of increasing complexity, starting with cell culture, small animals (rats and rabbits), and then large animals (goat and minipig) that more closely mimic nutritional, biomechanical, and surgical realities of human application. The use of standardized and reproducible experimental procedures and outcome measures is critical for judging relative efficacy. Finally, success will hinge on carefully designed clinical trials with well-defined patient selection criteria, gold-standard controls, and objective outcome metrics to assess performance in the early postoperative period.
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