Intradiscally injected MSCs remain in the nucleus pulposus at 24 weeks. (a) Disc in normal condition and one day after intradiscal injection of DiI-labeld syonovial MSCs into the normal disc. Macroscopic views of interbertebral discs and fluorescent microscopic views of nucleus pulposus are shown. (b) Fluorescent microscopic views for GFP and DiI synovial MSCs. Nucleus pulposus was aspirated in both groups, and synovial MSCs were intradiscally injected into the MSC group.