The dynamic disc model: a systematic review of the literature

Background: The intervertebral disc (IVD) has been implicated in the etiology and pathogenesis of spine pain. Examination and treatment approaches directed at the IVD often cite a biomechanical principle referred to as the dynamic disc model (DDM), which is hypothesised to account for positional changes of the nucleus pulposus (NP). The DDM proposes a predictable pattern of NP migration in response to movements and positioning; consequently, this model has served the basis for many clinical decisions. Objectives: The purpose of this manuscript was to systematically review the available research pertaining to the DDM in human discs. Methods: A literature review was conducted by two investigators independently using the MEDLINE, SPORTDiscus, EMBASE.com and CINAHL databases and the following key words independently and in combination: intervertebral disc, nucleus pulposus, nucleus migration, disc model, disc loading and dynamic disc model. Results from each researcher were pooled and studies were manually cross-referenced yielding 12 articles. Results: A predictable in vitro and in vivo pattern of NP movement was identified with the NP migrating anterior during extension and posterior during flexion in the normal IVD. Limited and contradictory data were available to support this model in the symptomatic and degenerative IVD. No studies were identified in the cervical and thoracic spine above the T10 level. Discussion: Available research supports the DDM of NP migration; however, an inconsistent pattern of migration may exist in patients with symptomatic and/or degenerative intervertebral discs. Future research is needed to evaluate the DDM in the cervical and thoracic spine and in abnormal discs.