Prevalence, clinical predictors, and mechanisms of resorption in lumbar disc herniation: a systematic review

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Study design Systematic review Background Conservative treatment is clinically preferred for lumbar disc herniation (LDH), and surgery is considered when patients’ life quality is still affected by LDH symptoms after three months’ conservative treatment. Spontaneous resorption of nucleus pulposus (NP) is common during conservative treatment. However, the current understanding for the mechanism of NP spontaneous resorption is lacking. Purpose The aim of this study was to elucidate the rate of NP spontaneous resorption, the evidence of predicting spontaneous resorption, and the pathophysiologic mechanisms of spontaneous resorption in the conservative management of LDH based on existing evidence from literature. Methods Studies related to NP spontaneous resorption of LDH were retried from PubMed, Embase, and Cochrane databases. Based on the studies conforming to inclusion criteria, a systematic review was generated for describing the proportion of NP spontaneous resorption, evidence of predicted resorption, and pathophysiologic mechanisms of spontaneous resorption. Results We reviewed a total of 34 articles dealing with the percentage of LDH resorption. The percentage of NP spontaneous resorption after conservative treatment was 76.6% (1684/2199), ranging from 20% to 96.2%. A total of 25 papers were reviewed, involving evidence of predicting resorption using predictors including NP size, inflammatory response to NP herniation, NP prolapse, the percentages edge-enhancing area and posterior longitudinal ligament coverage of the herniation measured by enhanced MRI. Moreover, we analyzed a total of 22 papers describing the pathophysiologic mechanisms of NP spontaneous resorption, where main mechanisms include inflammatory response, neovascular growth, macrophage infiltration, immune intervention, and matrix degradation. Conclusions A percentage of 76.6% in LDH patients undergo NP resorption. Prolapsed NP has a greater contact surface with blood system, which is easily to trigger immune response and thus promote spontaneous resorption. The mechanism of NP spontaneous resorption is mainly due to macrophage infiltration leading to immune response.