Repair and regenerative therapies of the annulus fibrosus of the intervertebral disc

Degeneration of the intervertebral disc is implicated as the main cause of low back pain. Current treatment strategies for degenerative disc disease, such as conservative treatments and surgeries, only relieve the symptoms of low back pain without treating the causes of underlying degeneration. Surgical treatments cannot reverse the degeneration of the intervertebral disc degeneration, and may even accelerate the degeneration. The development of tissue engineering and regenerative therapeutic strategies have brought new hope for repair and regeneration of the degenerated intervertebral disc. These strategies have been developed mainly targeting to the repair and regeneration of the nucleus pulposus of the degenerated but intervertebral disc. Although many studies that focused on the nucleus pulposus repair have achieved successes in laboratory settings but disc repair without giving much regard to annulus fibrosus could not recover the normal mechanical environment, which might make the disc degenerative change continuously exacerbate. Lately, the strategy to simultaneously repair the damaged annulus fibrosus and nucleus pulposus has attracted more attention, which could be considered to slow the disc degenerative rate and obtain better repair effect. An extensive literature search up to March 2015 for annulus fibrosus repair and regeneration in vitro or in vivo studies and clinical trials with the key words of "annulus fibrosus, repair, regeneration, tissue engineering, intervertebral disc and scaffold" were performed through PubMed, China National Knowledge Infrastructure and China Biology Medicine. The goal of this paper was to review the current research progress of annulus fibrosus repair and regeneration, and also suggest directions for future research